Merge ".mailmap: Correct two contributor names"

[mediawiki.git] / includes / libs / rdbms / database / Database.php

<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */
namespace Wikimedia\Rdbms;

use InvalidArgumentException;
use LogicException;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use RuntimeException;
use Stringable;
use Throwable;
use Wikimedia\AtEase\AtEase;
use Wikimedia\Rdbms\Database\DatabaseFlags;
use Wikimedia\Rdbms\Platform\SQLPlatform;
use Wikimedia\Rdbms\Replication\ReplicationReporter;
use Wikimedia\RequestTimeout\CriticalSectionProvider;
use Wikimedia\RequestTimeout\CriticalSectionScope;
use Wikimedia\ScopedCallback;
use Wikimedia\Telemetry\NoopTracer;
use Wikimedia\Telemetry\SpanInterface;
use Wikimedia\Telemetry\TracerInterface;

/**
 * A single concrete connection to a relational database.
 *
 * This is the base class for all connection-specific relational database handles.
 * No two instances of this class should share the same underlying network connection.
 *
 * @see IDatabase
 * @ingroup Database
 * @since 1.28
 */
abstract class Database implements Stringable, IDatabaseForOwner, IMaintainableDatabase, LoggerAwareInterface {
        /** @var CriticalSectionProvider|null */
        protected $csProvider;
        /** @var LoggerInterface */
        protected $logger;
        /** @var callable Error logging callback */
        protected $errorLogger;
        /** @var callable Deprecation logging callback */
        protected $deprecationLogger;
        /** @var callable|null */
        protected $profiler;
        /** @var TracerInterface */
        private $tracer;
        /** @var TransactionManager */
        private $transactionManager;

        /** @var DatabaseDomain */
        protected $currentDomain;
        /** @var DatabaseFlags */
        protected $flagsHolder;

        // phpcs:ignore MediaWiki.Commenting.PropertyDocumentation.ObjectTypeHintVar
        /** @var object|resource|null Database connection */
        protected $conn;

        /** @var string|null Readable name or host/IP of the database server */
        protected $serverName;
        /** @var bool Whether this PHP instance is for a CLI script */
        protected $cliMode;
        /** @var int|null Maximum seconds to wait on connection attempts */
        protected $connectTimeout;
        /** @var int|null Maximum seconds to wait on receiving query results */
        protected $receiveTimeout;
        /** @var string Agent name for query profiling */
        protected $agent;
        /** @var array<string,mixed> Connection parameters used by initConnection() and open() */
        protected $connectionParams;
        /** @var string[]|int[]|float[] SQL variables values to use for all new connections */
        protected $connectionVariables;
        /** @var int Row batch size to use for emulated INSERT SELECT queries */
        protected $nonNativeInsertSelectBatchSize;

        /** @var bool Whether to use SSL connections */
        protected $ssl;
        /** @var bool Whether to check for warnings */
        protected $strictWarnings;
        /** @var array Current LoadBalancer tracking information */
        protected $lbInfo = [];
        /** @var string|false Current SQL query delimiter */
        protected $delimiter = ';';

        /** @var string|bool|null Stashed value of html_errors INI setting */
        private $htmlErrors;

        /** @var array<string,array> Map of (lock name => (UNIX time,trx ID)) */
        protected $sessionNamedLocks = [];
        /** @var array<string,array<string, TempTableInfo>> Map of (DB name => table name => info) */
        protected $sessionTempTables = [];

        /** @var int Affected row count for the last statement to query() */
        protected $lastQueryAffectedRows = 0;
        /** @var int|null Insert (row) ID for the last statement to query() (null if not supported) */
        protected $lastQueryInsertId;

        /** @var int|null Affected row count for the last query method call; null if unspecified */
        protected $lastEmulatedAffectedRows;
        /** @var int|null Insert (row) ID for the last query method call; null if unspecified */
        protected $lastEmulatedInsertId;

        /** @var string Last error during connection; empty string if none */
        protected $lastConnectError = '';

        /** @var float UNIX timestamp of the last server response */
        private $lastPing = 0.0;
        /** @var float|null UNIX timestamp of the last committed write */
        private $lastWriteTime;
        /** @var string|false The last PHP error from a query or connection attempt */
        private $lastPhpError = false;

        /** @var int|null Current critical section numeric ID */
        private $csmId;
        /** @var string|null Last critical section caller name */
        private $csmFname;
        /** @var DBUnexpectedError|null Last unresolved critical section error */
        private $csmError;

        /** Whether the database is a file on disk */
        public const ATTR_DB_IS_FILE = 'db-is-file';
        /** Lock granularity is on the level of the entire database */
        public const ATTR_DB_LEVEL_LOCKING = 'db-level-locking';
        /** The SCHEMA keyword refers to a grouping of tables in a database */
        public const ATTR_SCHEMAS_AS_TABLE_GROUPS = 'supports-schemas';

        /** New Database instance will not be connected yet when returned */
        public const NEW_UNCONNECTED = 0;
        /** New Database instance will already be connected when returned */
        public const NEW_CONNECTED = 1;

        /** No errors occurred during the query */
        protected const ERR_NONE = 0;
        /** Retry query due to a connection loss detected while sending the query (session intact) */
        protected const ERR_RETRY_QUERY = 1;
        /** Abort query (no retries) due to a statement rollback (session/transaction intact) */
        protected const ERR_ABORT_QUERY = 2;
        /** Abort any current transaction, by rolling it back, due to an error during the query */
        protected const ERR_ABORT_TRX = 4;
        /** Abort and reset session due to server-side session-level state loss (locks, temp tables) */
        protected const ERR_ABORT_SESSION = 8;

        /** Assume that queries taking this long to yield connection loss errors are at fault */
        protected const DROPPED_CONN_BLAME_THRESHOLD_SEC = 3.0;

        /** @var string Idiom used when a cancelable atomic section started the transaction */
        private const NOT_APPLICABLE = 'n/a';

        /** How long before it is worth doing a dummy query to test the connection */
        private const PING_TTL = 1.0;
        /** Dummy SQL query */
        private const PING_QUERY = 'SELECT 1 AS ping';

        /** Hostname or IP address to use on all connections */
        protected const CONN_HOST = 'host';
        /** Database server username to use on all connections */
        protected const CONN_USER = 'user';
        /** Database server password to use on all connections */
        protected const CONN_PASSWORD = 'password';
        /** Database name to use on initial connection */
        protected const CONN_INITIAL_DB = 'dbname';
        /** Schema name to use on initial connection */
        protected const CONN_INITIAL_SCHEMA = 'schema';
        /** Table prefix to use on initial connection */
        protected const CONN_INITIAL_TABLE_PREFIX = 'tablePrefix';

        /** @var SQLPlatform */
        protected $platform;

        /** @var ReplicationReporter */
        protected $replicationReporter;

        /**
         * @note exceptions for missing libraries/drivers should be thrown in initConnection()
         * @param array $params Parameters passed from Database::factory()
         */
        public function __construct( array $params ) {
                $this->logger = $params['logger'] ?? new NullLogger();
                $this->transactionManager = new TransactionManager(
                        $this->logger,
                        $params['trxProfiler']
                );
                $this->connectionParams = [
                        self::CONN_HOST => ( isset( $params['host'] ) && $params['host'] !== '' )
                                ? $params['host']
                                : null,
                        self::CONN_USER => ( isset( $params['user'] ) && $params['user'] !== '' )
                                ? $params['user']
                                : null,
                        self::CONN_INITIAL_DB => ( isset( $params['dbname'] ) && $params['dbname'] !== '' )
                                ? $params['dbname']
                                : null,
                        self::CONN_INITIAL_SCHEMA => ( isset( $params['schema'] ) && $params['schema'] !== '' )
                                ? $params['schema']
                                : null,
                        self::CONN_PASSWORD => is_string( $params['password'] ) ? $params['password'] : null,
                        self::CONN_INITIAL_TABLE_PREFIX => (string)$params['tablePrefix']
                ];

                $this->lbInfo = $params['lbInfo'] ?? [];
                $this->connectionVariables = $params['variables'] ?? [];
                // Set SQL mode, default is turning them all off, can be overridden or skipped with null
                if ( is_string( $params['sqlMode'] ?? null ) ) {
                        $this->connectionVariables['sql_mode'] = $params['sqlMode'];
                }
                $flags = (int)$params['flags'];
                $this->flagsHolder = new DatabaseFlags( $flags );
                $this->ssl = $params['ssl'] ?? (bool)( $flags & self::DBO_SSL );
                $this->connectTimeout = $params['connectTimeout'] ?? null;
                $this->receiveTimeout = $params['receiveTimeout'] ?? null;
                $this->cliMode = (bool)$params['cliMode'];
                $this->agent = (string)$params['agent'];
                $this->serverName = $params['serverName'];
                $this->nonNativeInsertSelectBatchSize = $params['nonNativeInsertSelectBatchSize'] ?? 10000;
                $this->strictWarnings = !empty( $params['strictWarnings'] );

                $this->profiler = is_callable( $params['profiler'] ) ? $params['profiler'] : null;
                $this->errorLogger = $params['errorLogger'];
                $this->deprecationLogger = $params['deprecationLogger'];

                $this->csProvider = $params['criticalSectionProvider'] ?? null;

                // Set initial dummy domain until open() sets the final DB/prefix
                $this->currentDomain = new DatabaseDomain(
                        $params['dbname'] != '' ? $params['dbname'] : null,
                        $params['schema'] != '' ? $params['schema'] : null,
                        $params['tablePrefix']
                );
                $this->platform = new SQLPlatform(
                        $this,
                        $this->logger,
                        $this->currentDomain,
                        $this->errorLogger
                );
                $this->tracer = $params['tracer'] ?? new NoopTracer();
                // Children classes must set $this->replicationReporter.
        }

        /**
         * Initialize the connection to the database over the wire (or to local files)
         *
         * @throws LogicException
         * @throws InvalidArgumentException
         * @throws DBConnectionError
         * @since 1.31
         */
        final public function initConnection() {
                if ( $this->isOpen() ) {
                        throw new LogicException( __METHOD__ . ': already connected' );
                }
                // Establish the connection
                $this->open(
                        $this->connectionParams[self::CONN_HOST],
                        $this->connectionParams[self::CONN_USER],
                        $this->connectionParams[self::CONN_PASSWORD],
                        $this->connectionParams[self::CONN_INITIAL_DB],
                        $this->connectionParams[self::CONN_INITIAL_SCHEMA],
                        $this->connectionParams[self::CONN_INITIAL_TABLE_PREFIX]
                );
                $this->lastPing = microtime( true );
        }

        /**
         * Open a new connection to the database (closing any existing one)
         *
         * @param string|null $server Server host/address and optional port {@see connectionParams}
         * @param string|null $user User name {@see connectionParams}
         * @param string|null $password User password {@see connectionParams}
         * @param string|null $db Database name
         * @param string|null $schema Database schema name
         * @param string $tablePrefix
         * @throws DBConnectionError
         */
        abstract protected function open( $server, $user, $password, $db, $schema, $tablePrefix );

        /**
         * @return array Map of (Database::ATTR_* constant => value)
         * @since 1.31
         */
        public static function getAttributes() {
                return [];
        }

        /**
         * Set the PSR-3 logger interface to use.
         *
         * @param LoggerInterface $logger
         */
        public function setLogger( LoggerInterface $logger ) {
                $this->logger = $logger;
        }

        public function getServerInfo() {
                return $this->getServerVersion();
        }

        public function tablePrefix( $prefix = null ) {
                $old = $this->currentDomain->getTablePrefix();

                if ( $prefix !== null ) {
                        $this->currentDomain = new DatabaseDomain(
                                $this->currentDomain->getDatabase(),
                                $this->currentDomain->getSchema(),
                                $prefix
                        );
                        $this->platform->setCurrentDomain( $this->currentDomain );
                }

                return $old;
        }

        public function dbSchema( $schema = null ) {
                $old = $this->currentDomain->getSchema();

                if ( $schema !== null ) {
                        if ( $schema !== '' && $this->getDBname() === null ) {
                                throw new DBUnexpectedError(
                                        $this,
                                        "Cannot set schema to '$schema'; no database set"
                                );
                        }

                        $this->currentDomain = new DatabaseDomain(
                                $this->currentDomain->getDatabase(),
                                // DatabaseDomain uses null for unspecified schemas
                                ( $schema !== '' ) ? $schema : null,
                                $this->currentDomain->getTablePrefix()
                        );
                        $this->platform->setCurrentDomain( $this->currentDomain );
                }

                return (string)$old;
        }

        public function getLBInfo( $name = null ) {
                if ( $name === null ) {
                        return $this->lbInfo;
                }

                if ( array_key_exists( $name, $this->lbInfo ) ) {
                        return $this->lbInfo[$name];
                }

                return null;
        }

        public function setLBInfo( $nameOrArray, $value = null ) {
                if ( is_array( $nameOrArray ) ) {
                        $this->lbInfo = $nameOrArray;
                } elseif ( is_string( $nameOrArray ) ) {
                        if ( $value !== null ) {
                                $this->lbInfo[$nameOrArray] = $value;
                        } else {
                                unset( $this->lbInfo[$nameOrArray] );
                        }
                } else {
                        throw new InvalidArgumentException( "Got non-string key" );
                }
        }

        public function lastDoneWrites() {
                return $this->lastWriteTime;
        }

        /**
         * @return bool
         * @since 1.39
         * @internal For use by Database/LoadBalancer only
         */
        public function sessionLocksPending() {
                return (bool)$this->sessionNamedLocks;
        }

        /**
         * @return ?string Owner name of explicit transaction round being participating in; null if none
         */
        final protected function getTransactionRoundFname() {
                if ( $this->flagsHolder->hasImplicitTrxFlag() ) {
                        // LoadBalancer transaction round participation is enabled for this DB handle;
                        // get the owner of the active explicit transaction round (if any)
                        return $this->getLBInfo( self::LB_TRX_ROUND_FNAME );
                }

                return null;
        }

        public function isOpen() {
                return (bool)$this->conn;
        }

        public function getDomainID() {
                return $this->currentDomain->getId();
        }

        /**
         * Wrapper for addslashes()
         *
         * @param string $s String to be slashed.
         * @return string Slashed string.
         */
        abstract public function strencode( $s );

        /**
         * Set a custom error handler for logging errors during database connection
         */
        protected function installErrorHandler() {
                $this->lastPhpError = false;
                $this->htmlErrors = ini_set( 'html_errors', '0' );
                set_error_handler( [ $this, 'connectionErrorLogger' ] );
        }

        /**
         * Restore the previous error handler and return the last PHP error for this DB
         *
         * @return string|false
         */
        protected function restoreErrorHandler() {
                restore_error_handler();
                if ( $this->htmlErrors !== false ) {
                        ini_set( 'html_errors', $this->htmlErrors );
                }

                return $this->getLastPHPError();
        }

        /**
         * @return string|false Last PHP error for this DB (typically connection errors)
         */
        protected function getLastPHPError() {
                if ( $this->lastPhpError ) {
                        $error = preg_replace( '!\[<a.*</a>\]!', '', $this->lastPhpError );
                        $error = preg_replace( '!^.*?:\s?(.*)$!', '$1', $error );

                        return $error;
                }

                return false;
        }

        /**
         * Error handler for logging errors during database connection
         *
         * @internal This method should not be used outside of Database classes
         *
         * @param int|string $errno
         * @param string $errstr
         */
        public function connectionErrorLogger( $errno, $errstr ) {
                $this->lastPhpError = $errstr;
        }

        /**
         * Create a log context to pass to PSR-3 logger functions.
         *
         * @param array $extras Additional data to add to context
         * @return array
         */
        protected function getLogContext( array $extras = [] ) {
                return array_merge(
                        [
                                'db_server' => $this->getServerName(),
                                'db_name' => $this->getDBname(),
                                'db_user' => $this->connectionParams[self::CONN_USER] ?? null,
                        ],
                        $extras
                );
        }

        final public function close( $fname = __METHOD__ ) {
                $error = null; // error to throw after disconnecting

                $wasOpen = (bool)$this->conn;
                // This should mostly do nothing if the connection is already closed
                if ( $this->conn ) {
                        // Roll back any dangling transaction first
                        if ( $this->trxLevel() ) {
                                $error = $this->transactionManager->trxCheckBeforeClose( $this, $fname );
                                // Rollback the changes and run any callbacks as needed
                                $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
                                $this->runTransactionPostRollbackCallbacks();
                        }

                        // Close the actual connection in the binding handle
                        $closed = $this->closeConnection();
                } else {
                        $closed = true; // already closed; nothing to do
                }

                $this->conn = null;

                // Log any unexpected errors after having disconnected
                if ( $error !== null ) {
                        // T217819, T231443: this is probably just LoadBalancer trying to recover from
                        // errors and shutdown. Log any problems and move on since the request has to
                        // end one way or another. Throwing errors is not very useful at some point.
                        $this->logger->error( $error, [ 'db_log_category' => 'query' ] );
                }

                // Note that various subclasses call close() at the start of open(), which itself is
                // called by replaceLostConnection(). In that case, just because onTransactionResolution()
                // callbacks are pending does not mean that an exception should be thrown. Rather, they
                // will be executed after the reconnection step.
                if ( $wasOpen ) {
                        // Double check that no callbacks are dangling
                        $fnames = $this->pendingWriteAndCallbackCallers();
                        if ( $fnames ) {
                                throw new RuntimeException(
                                        "Transaction callbacks are still pending: " . implode( ', ', $fnames )
                                );
                        }
                }

                return $closed;
        }

        /**
         * Make sure there is an open connection handle (alive or not)
         *
         * This guards against fatal errors to the binding handle not being defined in cases
         * where open() was never called or close() was already called.
         *
         * @throws DBUnexpectedError
         */
        final protected function assertHasConnectionHandle() {
                if ( !$this->isOpen() ) {
                        throw new DBUnexpectedError( $this, "DB connection was already closed" );
                }
        }

        /**
         * Closes underlying database connection
         * @return bool Whether connection was closed successfully
         * @since 1.20
         */
        abstract protected function closeConnection();

        /**
         * Run a query and return a QueryStatus instance with the query result information
         *
         * This is meant to handle the basic command of actually sending a query to the
         * server via the driver. No implicit transaction, reconnection, nor retry logic
         * should happen here. The higher level query() method is designed to handle those
         * sorts of concerns. This method should not trigger such higher level methods.
         *
         * The lastError() and lastErrno() methods should meaningfully reflect what error,
         * if any, occurred during the last call to this method. Methods like executeQuery(),
         * query(), select(), insert(), update(), delete(), and upsert() implement their calls
         * to doQuery() such that an immediately subsequent call to lastError()/lastErrno()
         * meaningfully reflects any error that occurred during that public query method call.
         *
         * For SELECT queries, the result field contains either:
         *   - a) A driver-specific IResultWrapper describing the query results
         *   - b) False, on any query failure
         *
         * For non-SELECT queries, the result field contains either:
         *   - a) A driver-specific IResultWrapper, only on success
         *   - b) True, only on success (e.g. no meaningful result other than "OK")
         *   - c) False, on any query failure
         *
         * @param string $sql Single-statement SQL query
         * @return QueryStatus
         * @since 1.39
         */
        abstract protected function doSingleStatementQuery( string $sql ): QueryStatus;

        /**
         * Determine whether a write query affects a permanent table.
         * This includes pseudo-permanent tables.
         *
         * @param Query $query
         * @return bool
         */
        private function hasPermanentTable( Query $query ) {
                if ( $query->getVerb() === 'CREATE TEMPORARY' ) {
                        // Temporary table creation is allowed
                        return false;
                }
                $table = $query->getWriteTable();
                if ( $table === null ) {
                        // Parse error? Assume permanent.
                        return true;
                }
                [ $db, $pt ] = $this->platform->getDatabaseAndTableIdentifier( $table );
                $tempInfo = $this->sessionTempTables[$db][$pt] ?? null;
                return !$tempInfo || $tempInfo->pseudoPermanent;
        }

        /**
         * Register creation and dropping of temporary tables
         *
         * @param Query $query
         */
        protected function registerTempTables( Query $query ) {
                $table = $query->getWriteTable();
                if ( $table === null ) {
                        return;
                }
                switch ( $query->getVerb() ) {
                        case 'CREATE TEMPORARY':
                                [ $db, $pt ] = $this->platform->getDatabaseAndTableIdentifier( $table );
                                $this->sessionTempTables[$db][$pt] = new TempTableInfo(
                                        $this->transactionManager->getTrxId(),
                                        (bool)( $query->getFlags() & self::QUERY_PSEUDO_PERMANENT )
                                );
                                break;

                        case 'DROP':
                                [ $db, $pt ] = $this->platform->getDatabaseAndTableIdentifier( $table );
                                unset( $this->sessionTempTables[$db][$pt] );
                }
        }

        public function query( $sql, $fname = __METHOD__, $flags = 0 ) {
                if ( !( $sql instanceof Query ) ) {
                        $flags = (int)$flags; // b/c; this field used to be a bool
                        $sql = QueryBuilderFromRawSql::buildQuery( $sql, $flags, $this->currentDomain->getTablePrefix() );
                } else {
                        $flags = $sql->getFlags();
                }

                // Make sure that this caller is allowed to issue this query statement
                $this->assertQueryIsCurrentlyAllowed( $sql->getVerb(), $fname );

                // Send the query to the server and fetch any corresponding errors
                $status = $this->executeQuery( $sql, $fname, $flags );
                if ( $status->res === false ) {
                        // An error occurred; log, and, if needed, report an exception.
                        // Errors that corrupt the transaction/session state cannot be silenced.
                        $ignore = (
                                $this->flagsHolder::contains( $flags, self::QUERY_SILENCE_ERRORS ) &&
                                !$this->flagsHolder::contains( $status->flags, self::ERR_ABORT_SESSION ) &&
                                !$this->flagsHolder::contains( $status->flags, self::ERR_ABORT_TRX )
                        );
                        $this->reportQueryError( $status->message, $status->code, $sql->getSQL(), $fname, $ignore );
                }

                return $status->res;
        }

        /**
         * Execute a query without enforcing public (non-Database) caller restrictions.
         *
         * Retry it if there is a recoverable connection loss (e.g. no important state lost).
         *
         * This does not precheck for transaction/session state errors or critical section errors.
         *
         * @see Database::query()
         *
         * @param Query $sql SQL statement
         * @param string $fname Name of the calling function
         * @param int $flags Bit field of ISQLPlatform::QUERY_* constants
         * @return QueryStatus
         * @throws DBUnexpectedError
         * @since 1.34
         */
        final protected function executeQuery( $sql, $fname, $flags ) {
                $this->assertHasConnectionHandle();

                $isPermWrite = false;
                $isWrite = $sql->isWriteQuery();
                if ( $isWrite ) {
                        ChangedTablesTracker::recordQuery( $this->currentDomain, $sql );
                        // Permit temporary table writes on replica connections, but require a writable
                        // master connection for writes to persistent tables.
                        if ( $this->hasPermanentTable( $sql ) ) {
                                $isPermWrite = true;
                                $info = $this->getReadOnlyReason();
                                if ( $info ) {
                                        [ $reason, $source ] = $info;
                                        if ( $source === 'role' ) {
                                                throw new DBReadOnlyRoleError( $this, "Database is read-only: $reason" );
                                        } else {
                                                throw new DBReadOnlyError( $this, "Database is read-only: $reason" );
                                        }
                                }
                                // DBConnRef uses QUERY_REPLICA_ROLE to enforce replica roles during query()
                                if ( $this->flagsHolder::contains( $sql->getFlags(), self::QUERY_REPLICA_ROLE ) ) {
                                        throw new DBReadOnlyRoleError(
                                                $this,
                                                "Cannot write; target role is DB_REPLICA"
                                        );
                                }
                        }
                }

                // Whether a silent retry attempt is left for recoverable connection loss errors
                $retryLeft = !$this->flagsHolder::contains( $flags, self::QUERY_NO_RETRY );

                $cs = $this->commenceCriticalSection( __METHOD__ );

                do {
                        // Start a DBO_TRX wrapper transaction as needed (throw an error on failure)
                        if ( $this->beginIfImplied( $sql, $fname, $flags ) ) {
                                // Since begin() was called, any connection loss was already handled
                                $retryLeft = false;
                        }
                        // Send the query statement to the server and fetch any results.
                        $status = $this->attemptQuery( $sql, $fname, $isPermWrite );
                } while (
                        // An error occurred that can be recovered from via query retry
                        $this->flagsHolder::contains( $status->flags, self::ERR_RETRY_QUERY ) &&
                        // The retry has not been exhausted (consume it now)
                        // phpcs:ignore Generic.CodeAnalysis.AssignmentInCondition.FoundInWhileCondition
                        $retryLeft && !( $retryLeft = false )
                );

                // Register creation and dropping of temporary tables
                if ( $status->res ) {
                        $this->registerTempTables( $sql );
                }
                $this->completeCriticalSection( __METHOD__, $cs );

                return $status;
        }

        /**
         * Query method wrapper handling profiling, logging, affected row count tracking, and
         * automatic reconnections (without retry) on query failure due to connection loss
         *
         * Note that this does not handle DBO_TRX logic.
         *
         * This method handles profiling, debug logging, reconnection and the tracking of:
         *   - write callers
         *   - last write time
         *   - affected row count of the last write
         *   - whether writes occurred in a transaction
         *   - last successful query time (confirming that the connection was not dropped)
         *
         * @see doSingleStatementQuery()
         *
         * @param Query $sql SQL statement
         * @param string $fname Name of the calling function
         * @param bool $isPermWrite Whether it's a query writing to permanent tables
         * @return QueryStatus statement result
         * @throws DBUnexpectedError
         */
        private function attemptQuery(
                $sql,
                string $fname,
                bool $isPermWrite
        ) {
                // Transaction attributes before issuing this query
                $priorSessInfo = new CriticalSessionInfo(
                        $this->transactionManager->getTrxId(),
                        $this->transactionManager->explicitTrxActive(),
                        $this->transactionManager->pendingWriteCallers(),
                        $this->transactionManager->pendingPreCommitCallbackCallers(),
                        $this->sessionNamedLocks,
                        $this->sessionTempTables
                );
                // Get the transaction-aware SQL string used for profiling
                $generalizedSql = GeneralizedSql::newFromQuery(
                        $sql,
                        ( $this->replicationReporter->getTopologyRole() === self::ROLE_STREAMING_MASTER )
                                ? 'role-primary: '
                                : ''
                );
                // Add agent and calling method comments to the SQL
                $cStatement = $this->makeCommentedSql( $sql->getSQL(), $fname );
                // Start profile section
                $ps = $this->profiler ? ( $this->profiler )( $generalizedSql->stringify() ) : null;
                $startTime = microtime( true );

                // Clear any overrides from a prior "query method". Note that this does not affect
                // any such methods that are currently invoking query() itself since those query
                // methods set these fields before returning.
                $this->lastEmulatedAffectedRows = null;
                $this->lastEmulatedInsertId = null;

                // Record an OTEL span for this query.
                $writeTableName = $sql->getWriteTable();
                $spanName = $writeTableName ?
                        "Database {$sql->getVerb()} {$this->getDBname()}.{$writeTableName}" :
                        "Database {$sql->getVerb()} {$this->getDBname()}";
                $span = $this->tracer->createSpan( $spanName )
                        ->setSpanKind( SpanInterface::SPAN_KIND_CLIENT )
                        ->start();
                if ( $span->getContext()->isSampled() ) {
                        $span->setAttributes( [
                                'code.function' => $fname,
                                'db.namespace' => $this->getDBname(),
                                'db.operation.name' => $sql->getVerb(),
                                'db.query.text' => $generalizedSql->stringify(),
                                'db.system' => $this->getType(),
                                'server.address' => $this->getServerName(),
                                'db.collection.name' => $writeTableName, # nulls filtered out
                        ] );
                }

                $status = $this->doSingleStatementQuery( $cStatement );

                // End profile section
                $endTime = microtime( true );
                $queryRuntime = max( $endTime - $startTime, 0.0 );
                unset( $ps );
                $span->end();

                if ( $status->res !== false ) {
                        $this->lastPing = $endTime;
                        $span->setSpanStatus( SpanInterface::SPAN_STATUS_OK );
                } else {
                        $span->setSpanStatus( SpanInterface::SPAN_STATUS_ERROR )
                                ->setAttributes( [
                                'db.response.status_code' => $status->code,
                                'exception.message' => $status->message,
                        ] );
                }

                $affectedRowCount = $status->rowsAffected;
                $returnedRowCount = $status->rowsReturned;
                $this->lastQueryAffectedRows = $affectedRowCount;

                if ( $span->getContext()->isSampled() ) {
                        $span->setAttributes( [
                                'db.response.affected_rows' => $affectedRowCount,
                                'db.response.returned_rows' => $returnedRowCount,
                        ] );
                }

                if ( $status->res !== false ) {
                        if ( $isPermWrite ) {
                                if ( $this->trxLevel() ) {
                                        $this->transactionManager->transactionWritingIn(
                                                $this->getServerName(),
                                                $this->getDomainID(),
                                                $startTime
                                        );
                                        $this->transactionManager->updateTrxWriteQueryReport(
                                                $sql->getSQL(),
                                                $queryRuntime,
                                                $affectedRowCount,
                                                $fname
                                        );
                                } else {
                                        $this->lastWriteTime = $endTime;
                                }
                        }
                }

                $this->transactionManager->recordQueryCompletion(
                        $generalizedSql,
                        $startTime,
                        $isPermWrite,
                        $isPermWrite ? $affectedRowCount : $returnedRowCount,
                        $this->getServerName()
                );

                // Check if the query failed...
                $status->flags = $this->handleErroredQuery( $status, $sql, $fname, $queryRuntime, $priorSessInfo );
                // Avoid the overhead of logging calls unless debug mode is enabled
                if ( $this->flagsHolder->getFlag( self::DBO_DEBUG ) ) {
                        $this->logger->debug(
                                "{method} [{runtime_ms}ms] {db_server}: {sql}",
                                $this->getLogContext( [
                                        'method' => $fname,
                                        'sql' => $sql->getSQL(),
                                        'domain' => $this->getDomainID(),
                                        'runtime_ms' => round( $queryRuntime * 1000, 3 ),
                                        'db_log_category' => 'query'
                                ] )
                        );
                }

                return $status;
        }

        private function handleErroredQuery( QueryStatus $status, $sql, $fname, $queryRuntime, $priorSessInfo ) {
                $errflags = self::ERR_NONE;
                $error = $status->message;
                $errno = $status->code;
                if ( $status->res !== false ) {
                        // Statement succeeded
                        return $errflags;
                }
                if ( $this->isConnectionError( $errno ) ) {
                        // Connection lost before or during the query...
                        // Determine how to proceed given the lost session state
                        $connLossFlag = $this->assessConnectionLoss(
                                $sql->getVerb(),
                                $queryRuntime,
                                $priorSessInfo
                        );
                        // Update session state tracking and try to reestablish a connection
                        $reconnected = $this->replaceLostConnection( $errno, __METHOD__ );
                        // Check if important server-side session-level state was lost
                        if ( $connLossFlag >= self::ERR_ABORT_SESSION ) {
                                $ex = $this->getQueryException( $error, $errno, $sql->getSQL(), $fname );
                                $this->transactionManager->setSessionError( $ex );
                        }
                        // Check if important server-side transaction-level state was lost
                        if ( $connLossFlag >= self::ERR_ABORT_TRX ) {
                                $ex = $this->getQueryException( $error, $errno, $sql->getSQL(), $fname );
                                $this->transactionManager->setTransactionError( $ex );
                        }
                        // Check if the query should be retried (having made the reconnection attempt)
                        if ( $connLossFlag === self::ERR_RETRY_QUERY ) {
                                $errflags |= ( $reconnected ? self::ERR_RETRY_QUERY : self::ERR_ABORT_QUERY );
                        } else {
                                $errflags |= $connLossFlag;
                        }
                } elseif ( $this->isKnownStatementRollbackError( $errno ) ) {
                        // Query error triggered a server-side statement-only rollback...
                        $errflags |= self::ERR_ABORT_QUERY;
                        if ( $this->trxLevel() ) {
                                // Allow legacy callers to ignore such errors via QUERY_IGNORE_DBO_TRX and
                                // try/catch. However, a deprecation notice will be logged on the next query.
                                $cause = [ $error, $errno, $fname ];
                                $this->transactionManager->setTrxStatusIgnoredCause( $cause );
                        }
                } elseif ( $this->trxLevel() ) {
                        // Some other error occurred during the query, within a transaction...
                        // Server-side handling of errors during transactions varies widely depending on
                        // the RDBMS type and configuration. There are several possible results: (a) the
                        // whole transaction is rolled back, (b) only the queries after BEGIN are rolled
                        // back, (c) the transaction is marked as "aborted" and a ROLLBACK is required
                        // before other queries are permitted. For compatibility reasons, pessimistically
                        // require a ROLLBACK query (not using SAVEPOINT) before allowing other queries.
                        $ex = $this->getQueryException( $error, $errno, $sql->getSQL(), $fname );
                        $this->transactionManager->setTransactionError( $ex );
                        $errflags |= self::ERR_ABORT_TRX;
                } else {
                        // Some other error occurred during the query, without a transaction...
                        $errflags |= self::ERR_ABORT_QUERY;
                }

                return $errflags;
        }

        /**
         * @param string $sql
         * @param string $fname
         * @return string
         */
        private function makeCommentedSql( $sql, $fname ): string {
                // Add trace comment to the begin of the sql string, right after the operator.
                // Or, for one-word queries (like "BEGIN" or COMMIT") add it to the end (T44598).
                // NOTE: Don't add varying ids such as request id or session id to the comment.
                // It would break aggregation of similar queries in analysis tools (see T193050#7512149)
                $encName = preg_replace( '/[\x00-\x1F\/]/', '-', "$fname {$this->agent}" );
                return preg_replace( '/\s|$/', " /* $encName */ ", $sql, 1 );
        }

        /**
         * Start an implicit transaction if DBO_TRX is enabled and no transaction is active
         *
         * @param Query $sql SQL statement
         * @param string $fname
         * @param int $flags Bit field of ISQLPlatform::QUERY_* constants
         * @return bool Whether an implicit transaction was started
         * @throws DBError
         */
        private function beginIfImplied( $sql, $fname, $flags ) {
                if ( !$this->trxLevel() && $this->flagsHolder->hasApplicableImplicitTrxFlag( $flags ) ) {
                        if ( $this->platform->isTransactableQuery( $sql ) ) {
                                $this->begin( __METHOD__ . " ($fname)", self::TRANSACTION_INTERNAL );
                                $this->transactionManager->turnOnAutomatic();

                                return true;
                        }
                }

                return false;
        }

        /**
         * Check if callers outside of Database can run the given query given the session state
         *
         * In order to keep the DB handle's session state tracking in sync, certain queries
         * like "USE", "BEGIN", "COMMIT", and "ROLLBACK" must not be issued directly from
         * outside callers. Such commands should only be issued through dedicated methods
         * like selectDomain(), begin(), commit(), and rollback(), respectively.
         *
         * This also checks if the session state tracking was corrupted by a prior exception.
         *
         * @param string $verb
         * @param string $fname
         * @throws DBUnexpectedError
         * @throws DBTransactionStateError
         */
        private function assertQueryIsCurrentlyAllowed( string $verb, string $fname ) {
                if ( $verb === 'USE' ) {
                        throw new DBUnexpectedError( $this, "Got USE query; use selectDomain() instead" );
                }

                if ( $verb === 'ROLLBACK' ) {
                        // Whole transaction rollback is used for recovery
                        // @TODO: T269161; prevent "BEGIN"/"COMMIT"/"ROLLBACK" from outside callers
                        return;
                }

                if ( $this->csmError ) {
                        throw new DBTransactionStateError(
                                $this,
                                "Cannot execute query from $fname while session state is out of sync",
                                [],
                                $this->csmError
                        );
                }

                $this->transactionManager->assertSessionStatus( $this, $fname );

                if ( $verb !== 'ROLLBACK TO SAVEPOINT' ) {
                        $this->transactionManager->assertTransactionStatus(
                                $this,
                                $this->deprecationLogger,
                                $fname
                        );
                }
        }

        /**
         * Determine how to handle a connection lost discovered during a query attempt
         *
         * This checks if explicit transactions, pending transaction writes, and important
         * session-level state (locks, temp tables) was lost. Point-in-time read snapshot loss
         * is considered acceptable for DBO_TRX logic.
         *
         * If state was lost, but that loss was discovered during a ROLLBACK that would have
         * destroyed that state anyway, treat the error as recoverable.
         *
         * @param string $verb SQL query verb
         * @param float $walltime How many seconds passes while attempting the query
         * @param CriticalSessionInfo $priorSessInfo Session state just before the query
         * @return int Recovery approach. One of the following ERR_* class constants:
         *   - Database::ERR_RETRY_QUERY: reconnect silently, retry query
         *   - Database::ERR_ABORT_QUERY: reconnect silently, do not retry query
         *   - Database::ERR_ABORT_TRX: reconnect, throw error, enforce transaction rollback
         *   - Database::ERR_ABORT_SESSION: reconnect, throw error, enforce session rollback
         */
        private function assessConnectionLoss(
                string $verb,
                float $walltime,
                CriticalSessionInfo $priorSessInfo
        ) {
                if ( $walltime < self::DROPPED_CONN_BLAME_THRESHOLD_SEC ) {
                        // Query failed quickly; the connection was probably lost before the query was sent
                        $res = self::ERR_RETRY_QUERY;
                } else {
                        // Query took a long time; the connection was probably lost during query execution
                        $res = self::ERR_ABORT_QUERY;
                }

                // List of problems causing session/transaction state corruption
                $blockers = [];
                // Loss of named locks breaks future callers relying on those locks for critical sections
                foreach ( $priorSessInfo->namedLocks as $lockName => $lockInfo ) {
                        if ( $lockInfo['trxId'] && $lockInfo['trxId'] === $priorSessInfo->trxId ) {
                                // Treat lost locks acquired during the lost transaction as a transaction state
                                // problem. Connection loss on ROLLBACK (non-SAVEPOINT) is tolerable since
                                // rollback automatically triggered server-side.
                                if ( $verb !== 'ROLLBACK' ) {
                                        $res = max( $res, self::ERR_ABORT_TRX );
                                        $blockers[] = "named lock '$lockName'";
                                }
                        } else {
                                // Treat lost locks acquired either during prior transactions or during no
                                // transaction as a session state problem.
                                $res = max( $res, self::ERR_ABORT_SESSION );
                                $blockers[] = "named lock '$lockName'";
                        }
                }
                // Loss of temp tables breaks future callers relying on those tables for queries
                foreach ( $priorSessInfo->tempTables as $domainTempTables ) {
                        foreach ( $domainTempTables as $tableName => $tableInfo ) {
                                if ( $tableInfo->trxId && $tableInfo->trxId === $priorSessInfo->trxId ) {
                                        // Treat lost temp tables created during the lost transaction as a
                                        // transaction state problem. Connection loss on ROLLBACK (non-SAVEPOINT)
                                        // is tolerable since rollback automatically triggered server-side.
                                        if ( $verb !== 'ROLLBACK' ) {
                                                $res = max( $res, self::ERR_ABORT_TRX );
                                                $blockers[] = "temp table '$tableName'";
                                        }
                                } else {
                                        // Treat lost temp tables created either during prior transactions or during
                                        // no transaction as a session state problem.
                                        $res = max( $res, self::ERR_ABORT_SESSION );
                                        $blockers[] = "temp table '$tableName'";
                                }
                        }
                }
                // Loss of transaction writes breaks future callers and DBO_TRX logic relying on those
                // writes to be atomic and still pending. Connection loss on ROLLBACK (non-SAVEPOINT) is
                // tolerable since rollback automatically triggered server-side.
                if ( $priorSessInfo->trxWriteCallers && $verb !== 'ROLLBACK' ) {
                        $res = max( $res, self::ERR_ABORT_TRX );
                        $blockers[] = 'uncommitted writes';
                }
                if ( $priorSessInfo->trxPreCommitCbCallers && $verb !== 'ROLLBACK' ) {
                        $res = max( $res, self::ERR_ABORT_TRX );
                        $blockers[] = 'pre-commit callbacks';
                }
                if ( $priorSessInfo->trxExplicit && $verb !== 'ROLLBACK' && $verb !== 'COMMIT' ) {
                        // Transaction automatically rolled back, breaking the expectations of callers
                        // relying on the continued existence of that transaction for things like atomic
                        // writes, serializability, or reads from the same point-in-time snapshot. If the
                        // connection loss occured on ROLLBACK (non-SAVEPOINT) or COMMIT, then we do not
                        // need to mark the transaction state as corrupt, since no transaction would still
                        // be open even if the query did succeed (T127428).
                        $res = max( $res, self::ERR_ABORT_TRX );
                        $blockers[] = 'explicit transaction';
                }

                if ( $blockers ) {
                        $this->logger->warning(
                                "cannot reconnect to {db_server} silently: {error}",
                                $this->getLogContext( [
                                        'error' => 'session state loss (' . implode( ', ', $blockers ) . ')',
                                        'exception' => new RuntimeException(),
                                        'db_log_category' => 'connection'
                                ] )
                        );
                }

                return $res;
        }

        /**
         * Clean things up after session (and thus transaction) loss before reconnect
         */
        private function handleSessionLossPreconnect() {
                // Clean up tracking of session-level things...
                // https://mariadb.com/kb/en/create-table/#create-temporary-table
                // https://www.postgresql.org/docs/9.2/static/sql-createtable.html (ignoring ON COMMIT)
                $this->sessionTempTables = [];
                // https://mariadb.com/kb/en/get_lock/
                // https://www.postgresql.org/docs/9.4/static/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS
                $this->sessionNamedLocks = [];
                // Session loss implies transaction loss (T67263)
                $this->transactionManager->onSessionLoss( $this );
                // Clear additional subclass fields
                $this->doHandleSessionLossPreconnect();
        }

        /**
         * Reset any additional subclass trx* and session* fields
         */
        protected function doHandleSessionLossPreconnect() {
                // no-op
        }

        /**
         * Checks whether the cause of the error is detected to be a timeout.
         *
         * It returns false by default, and not all engines support detecting this yet.
         * If this returns false, it will be treated as a generic query error.
         *
         * @param int|string $errno Error number
         * @return bool
         * @since 1.39
         */
        protected function isQueryTimeoutError( $errno ) {
                return false;
        }

        /**
         * Report a query error
         *
         * If $ignore is set, emit a DEBUG level log entry and continue,
         * otherwise, emit an ERROR level log entry and throw an exception.
         *
         * @param string $error
         * @param int|string $errno
         * @param string $sql
         * @param string $fname
         * @param bool $ignore Whether to just log an error rather than throw an exception
         * @throws DBQueryError
         */
        public function reportQueryError( $error, $errno, $sql, $fname, $ignore = false ) {
                if ( $ignore ) {
                        $this->logger->debug(
                                "SQL ERROR (ignored): $error",
                                [ 'db_log_category' => 'query' ]
                        );
                } else {
                        throw $this->getQueryExceptionAndLog( $error, $errno, $sql, $fname );
                }
        }

        /**
         * @param string $error
         * @param string|int $errno
         * @param string $sql
         * @param string $fname
         * @return DBError
         */
        private function getQueryExceptionAndLog( $error, $errno, $sql, $fname ) {
                // Information that instances of the same problem have in common should
                // not be normalized (T255202).
                $this->logger->error(
                        "Error $errno from $fname, {error} {sql1line} {db_server}",
                        $this->getLogContext( [
                                'method' => __METHOD__,
                                'errno' => $errno,
                                'error' => $error,
                                'sql1line' => mb_substr( str_replace( "\n", "\\n", $sql ), 0, 5 * 1024 ),
                                'fname' => $fname,
                                'db_log_category' => 'query',
                                'exception' => new RuntimeException()
                        ] )
                );
                return $this->getQueryException( $error, $errno, $sql, $fname );
        }

        /**
         * @param string $error
         * @param string|int $errno
         * @param string $sql
         * @param string $fname
         * @return DBError
         */
        private function getQueryException( $error, $errno, $sql, $fname ) {
                if ( $this->isQueryTimeoutError( $errno ) ) {
                        return new DBQueryTimeoutError( $this, $error, $errno, $sql, $fname );
                } elseif ( $this->isConnectionError( $errno ) ) {
                        return new DBQueryDisconnectedError( $this, $error, $errno, $sql, $fname );
                } else {
                        return new DBQueryError( $this, $error, $errno, $sql, $fname );
                }
        }

        /**
         * @param string $error
         * @return DBConnectionError
         */
        final protected function newExceptionAfterConnectError( $error ) {
                // Connection was not fully initialized and is not safe for use.
                // Stash any error associated with the handle before destroying it.
                $this->lastConnectError = $error;
                $this->conn = null;

                $this->logger->error(
                        "Error connecting to {db_server} as user {db_user}: {error}",
                        $this->getLogContext( [
                                'error' => $error,
                                'exception' => new RuntimeException(),
                                'db_log_category' => 'connection',
                        ] )
                );

                return new DBConnectionError( $this, $error );
        }

        /**
         * Get a SelectQueryBuilder bound to this connection. This is overridden by
         * DBConnRef.
         *
         * @return SelectQueryBuilder
         */
        public function newSelectQueryBuilder(): SelectQueryBuilder {
                return new SelectQueryBuilder( $this );
        }

        /**
         * Get a UnionQueryBuilder bound to this connection. This is overridden by
         * DBConnRef.
         *
         * @return UnionQueryBuilder
         */
        public function newUnionQueryBuilder(): UnionQueryBuilder {
                return new UnionQueryBuilder( $this );
        }

        /**
         * Get an UpdateQueryBuilder bound to this connection. This is overridden by
         * DBConnRef.
         *
         * @return UpdateQueryBuilder
         */
        public function newUpdateQueryBuilder(): UpdateQueryBuilder {
                return new UpdateQueryBuilder( $this );
        }

        /**
         * Get a DeleteQueryBuilder bound to this connection. This is overridden by
         * DBConnRef.
         *
         * @return DeleteQueryBuilder
         */
        public function newDeleteQueryBuilder(): DeleteQueryBuilder {
                return new DeleteQueryBuilder( $this );
        }

        /**
         * Get a InsertQueryBuilder bound to this connection. This is overridden by
         * DBConnRef.
         *
         * @return InsertQueryBuilder
         */
        public function newInsertQueryBuilder(): InsertQueryBuilder {
                return new InsertQueryBuilder( $this );
        }

        /**
         * Get a ReplaceQueryBuilder bound to this connection. This is overridden by
         * DBConnRef.
         *
         * @return ReplaceQueryBuilder
         */
        public function newReplaceQueryBuilder(): ReplaceQueryBuilder {
                return new ReplaceQueryBuilder( $this );
        }

        public function selectField(
                $tables, $var, $cond = '', $fname = __METHOD__, $options = [], $join_conds = []
        ) {
                if ( $var === '*' ) {
                        throw new DBUnexpectedError( $this, "Cannot use a * field" );
                } elseif ( is_array( $var ) && count( $var ) !== 1 ) {
                        throw new DBUnexpectedError( $this, 'Cannot use more than one field' );
                }

                $options = $this->platform->normalizeOptions( $options );
                $options['LIMIT'] = 1;

                $res = $this->select( $tables, $var, $cond, $fname, $options, $join_conds );
                if ( $res === false ) {
                        throw new DBUnexpectedError( $this, "Got false from select()" );
                }

                $row = $res->fetchRow();
                if ( $row === false ) {
                        return false;
                }

                return reset( $row );
        }

        public function selectFieldValues(
                $tables, $var, $cond = '', $fname = __METHOD__, $options = [], $join_conds = []
        ): array {
                if ( $var === '*' ) {
                        throw new DBUnexpectedError( $this, "Cannot use a * field" );
                } elseif ( !is_string( $var ) ) {
                        throw new DBUnexpectedError( $this, "Cannot use an array of fields" );
                }

                $options = $this->platform->normalizeOptions( $options );
                $res = $this->select( $tables, [ 'value' => $var ], $cond, $fname, $options, $join_conds );
                if ( $res === false ) {
                        throw new DBUnexpectedError( $this, "Got false from select()" );
                }

                $values = [];
                foreach ( $res as $row ) {
                        $values[] = $row->value;
                }

                return $values;
        }

        public function select(
                $tables, $vars, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ) {
                $options = (array)$options;
                // Don't turn this into using platform directly, DatabaseMySQL overrides this.
                $sql = $this->selectSQLText( $tables, $vars, $conds, $fname, $options, $join_conds );
                // Treat SELECT queries with FOR UPDATE as writes. This matches
                // how MySQL enforces read_only (FOR SHARE and LOCK IN SHADE MODE are allowed).
                $flags = in_array( 'FOR UPDATE', $options, true )
                        ? self::QUERY_CHANGE_ROWS
                        : self::QUERY_CHANGE_NONE;

                $query = new Query( $sql, $flags, 'SELECT' );
                return $this->query( $query, $fname );
        }

        public function selectRow( $tables, $vars, $conds, $fname = __METHOD__,
                $options = [], $join_conds = []
        ) {
                $options = (array)$options;
                $options['LIMIT'] = 1;

                $res = $this->select( $tables, $vars, $conds, $fname, $options, $join_conds );
                if ( $res === false ) {
                        throw new DBUnexpectedError( $this, "Got false from select()" );
                }

                if ( !$res->numRows() ) {
                        return false;
                }

                return $res->fetchObject();
        }

        /**
         * @inheritDoc
         */
        public function estimateRowCount(
                $tables, $var = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ): int {
                $conds = $this->platform->normalizeConditions( $conds, $fname );
                $column = $this->platform->extractSingleFieldFromList( $var );
                if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
                        $conds[] = "$column IS NOT NULL";
                }

                $res = $this->select(
                        $tables, [ 'rowcount' => 'COUNT(*)' ], $conds, $fname, $options, $join_conds
                );
                $row = $res ? $res->fetchRow() : [];

                return isset( $row['rowcount'] ) ? (int)$row['rowcount'] : 0;
        }

        public function selectRowCount(
                $tables, $var = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ): int {
                $conds = $this->platform->normalizeConditions( $conds, $fname );
                $column = $this->platform->extractSingleFieldFromList( $var );
                if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
                        $conds[] = "$column IS NOT NULL";
                }
                if ( in_array( 'DISTINCT', (array)$options ) ) {
                        if ( $column === null ) {
                                throw new DBUnexpectedError( $this,
                                        '$var cannot be empty when the DISTINCT option is given' );
                        }
                        $innerVar = $column;
                } else {
                        $innerVar = '1';
                }

                $res = $this->select(
                        [
                                'tmp_count' => $this->platform->buildSelectSubquery(
                                        $tables,
                                        $innerVar,
                                        $conds,
                                        $fname,
                                        $options,
                                        $join_conds
                                )
                        ],
                        [ 'rowcount' => 'COUNT(*)' ],
                        [],
                        $fname
                );
                $row = $res ? $res->fetchRow() : [];

                return isset( $row['rowcount'] ) ? (int)$row['rowcount'] : 0;
        }

        public function lockForUpdate(
                $table, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ) {
                if ( !$this->trxLevel() && !$this->flagsHolder->hasImplicitTrxFlag() ) {
                        throw new DBUnexpectedError(
                                $this,
                                __METHOD__ . ': no transaction is active nor is DBO_TRX set'
                        );
                }

                $options = (array)$options;
                $options[] = 'FOR UPDATE';

                return $this->selectRowCount( $table, '*', $conds, $fname, $options, $join_conds );
        }

        public function fieldExists( $table, $field, $fname = __METHOD__ ) {
                $info = $this->fieldInfo( $table, $field );

                return (bool)$info;
        }

        abstract public function tableExists( $table, $fname = __METHOD__ );

        public function indexExists( $table, $index, $fname = __METHOD__ ) {
                $info = $this->indexInfo( $table, $index, $fname );

                return (bool)$info;
        }

        public function indexUnique( $table, $index, $fname = __METHOD__ ) {
                $info = $this->indexInfo( $table, $index, $fname );

                return $info ? $info['unique'] : null;
        }

        /**
         * Get information about an index into an object
         *
         * @param string $table The unqualified name of a table
         * @param string $index Index name
         * @param string $fname Calling function name
         * @return array<string,mixed>|false Index info map; false if it does not exist
         * @phan-return array{unique:bool}|false
         */
        abstract public function indexInfo( $table, $index, $fname = __METHOD__ );

        public function insert( $table, $rows, $fname = __METHOD__, $options = [] ) {
                $query = $this->platform->dispatchingInsertSqlText( $table, $rows, $options );
                if ( !$query ) {
                        return true;
                }
                $this->query( $query, $fname );
                if ( $this->strictWarnings ) {
                        $this->checkInsertWarnings( $query, $fname );
                }
                return true;
        }

        /**
         * Check for warnings after performing an INSERT query, and throw exceptions
         * if necessary.
         *
         * @param Query $query
         * @param string $fname
         * @return void
         */
        protected function checkInsertWarnings( Query $query, $fname ) {
        }

        public function update( $table, $set, $conds, $fname = __METHOD__, $options = [] ) {
                $query = $this->platform->updateSqlText( $table, $set, $conds, $options );
                $this->query( $query, $fname );

                return true;
        }

        public function databasesAreIndependent() {
                return false;
        }

        final public function selectDomain( $domain ) {
                $cs = $this->commenceCriticalSection( __METHOD__ );

                try {
                        $this->doSelectDomain( DatabaseDomain::newFromId( $domain ) );
                } catch ( DBError $e ) {
                        $this->completeCriticalSection( __METHOD__, $cs );
                        throw $e;
                }

                $this->completeCriticalSection( __METHOD__, $cs );
        }

        /**
         * @param DatabaseDomain $domain
         * @throws DBConnectionError
         * @throws DBError
         * @since 1.32
         */
        protected function doSelectDomain( DatabaseDomain $domain ) {
                $this->currentDomain = $domain;
                $this->platform->setCurrentDomain( $this->currentDomain );
        }

        public function getDBname() {
                return $this->currentDomain->getDatabase();
        }

        public function getServer() {
                return $this->connectionParams[self::CONN_HOST] ?? null;
        }

        public function getServerName() {
                return $this->serverName ?? $this->getServer() ?? 'unknown';
        }

        public function addQuotes( $s ) {
                if ( $s instanceof RawSQLValue ) {
                        return $s->toSql();
                }
                if ( $s instanceof Blob ) {
                        $s = $s->fetch();
                }
                if ( $s === null ) {
                        return 'NULL';
                } elseif ( is_bool( $s ) ) {
                        return (string)(int)$s;
                } elseif ( is_int( $s ) ) {
                        return (string)$s;
                } else {
                        return "'" . $this->strencode( $s ) . "'";
                }
        }

        public function expr( string $field, string $op, $value ): Expression {
                return new Expression( $field, $op, $value );
        }

        public function andExpr( array $conds ): AndExpressionGroup {
                return AndExpressionGroup::newFromArray( $conds );
        }

        public function orExpr( array $conds ): OrExpressionGroup {
                return OrExpressionGroup::newFromArray( $conds );
        }

        public function replace( $table, $uniqueKeys, $rows, $fname = __METHOD__ ) {
                $uniqueKey = $this->platform->normalizeUpsertParams( $uniqueKeys, $rows );
                if ( !$rows ) {
                        return;
                }
                $affectedRowCount = 0;
                $insertId = null;
                $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
                try {
                        foreach ( $rows as $row ) {
                                // Delete any conflicting rows (including ones inserted from $rows)
                                $query = $this->platform->deleteSqlText(
                                        $table,
                                        [ $this->platform->makeKeyCollisionCondition( [ $row ], $uniqueKey ) ]
                                );
                                $this->query( $query, $fname );
                                // Insert the new row
                                $query = $this->platform->dispatchingInsertSqlText( $table, $row, [] );
                                $this->query( $query, $fname );
                                $affectedRowCount += $this->lastQueryAffectedRows;
                                $insertId = $insertId ?: $this->lastQueryInsertId;
                        }
                        $this->endAtomic( $fname );
                } catch ( DBError $e ) {
                        $this->cancelAtomic( $fname );
                        throw $e;
                }
                $this->lastEmulatedAffectedRows = $affectedRowCount;
                $this->lastEmulatedInsertId = $insertId;
        }

        public function upsert( $table, array $rows, $uniqueKeys, array $set, $fname = __METHOD__ ) {
                $uniqueKey = $this->platform->normalizeUpsertParams( $uniqueKeys, $rows );
                if ( !$rows ) {
                        return true;
                }
                $this->platform->assertValidUpsertSetArray( $set, $uniqueKey, $rows );

                $encTable = $this->tableName( $table );
                $sqlColumnAssignments = $this->makeList( $set, self::LIST_SET );
                // Get any AUTO_INCREMENT/SERIAL column for this table so we can set insertId()
                $autoIncrementColumn = $this->getInsertIdColumnForUpsert( $table );
                // Check if there is a SQL assignment expression in $set (as generated by SQLPlatform::buildExcludedValue)
                $useWith = (bool)array_filter(
                        $set,
                        static function ( $v, $k ) {
                                return $v instanceof RawSQLValue || is_int( $k );
                        },
                        ARRAY_FILTER_USE_BOTH
                );
                // Subclasses might need explicit type casting within "WITH...AS (VALUES ...)"
                // so that these CTE rows can be referenced within the SET clause assigments.
                $typeByColumn = $useWith ? $this->getValueTypesForWithClause( $table ) : [];

                $first = true;
                $affectedRowCount = 0;
                $insertId = null;
                $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
                try {
                        foreach ( $rows as $row ) {
                                // Update any existing conflicting row (including ones inserted from $rows)
                                [ $sqlColumns, $sqlTuples, $sqlVals ] = $this->platform->makeInsertLists(
                                        [ $row ],
                                        '__',
                                        $typeByColumn
                                );
                                $sqlConditions = $this->platform->makeKeyCollisionCondition(
                                        [ $row ],
                                        $uniqueKey
                                );
                                $query = new Query(
                                        ( $useWith ? "WITH __VALS ($sqlVals) AS (VALUES $sqlTuples) " : "" ) .
                                                "UPDATE $encTable SET $sqlColumnAssignments " .
                                                "WHERE ($sqlConditions)",
                                        self::QUERY_CHANGE_ROWS,
                                        'UPDATE',
                                        $table
                                );
                                $this->query( $query, $fname );
                                $rowsUpdated = $this->lastQueryAffectedRows;
                                $affectedRowCount += $rowsUpdated;
                                if ( $rowsUpdated > 0 ) {
                                        // Conflicting row found and updated
                                        if ( $first && $autoIncrementColumn !== null ) {
                                                // @TODO: use "RETURNING" instead (when supported by SQLite)
                                                $query = new Query(
                                                        "SELECT $autoIncrementColumn AS id FROM $encTable " .
                                                        "WHERE ($sqlConditions)",
                                                        self::QUERY_CHANGE_NONE,
                                                        'SELECT'
                                                );
                                                $sRes = $this->query( $query, $fname, self::QUERY_CHANGE_ROWS );
                                                $insertId = (int)$sRes->fetchRow()['id'];
                                        }
                                } else {
                                        // No conflicting row found
                                        $query = new Query(
                                                "INSERT INTO $encTable ($sqlColumns) VALUES $sqlTuples",
                                                self::QUERY_CHANGE_ROWS,
                                                'INSERT',
                                                $table
                                        );
                                        $this->query( $query, $fname );
                                        $affectedRowCount += $this->lastQueryAffectedRows;
                                }
                                $first = false;
                        }
                        $this->endAtomic( $fname );
                } catch ( DBError $e ) {
                        $this->cancelAtomic( $fname );
                        throw $e;
                }
                $this->lastEmulatedAffectedRows = $affectedRowCount;
                $this->lastEmulatedInsertId = $insertId;
                return true;
        }

        /**
         * @param string $table The unqualified name of a table
         * @return string|null The AUTO_INCREMENT/SERIAL column; null if not needed
         */
        protected function getInsertIdColumnForUpsert( $table ) {
                return null;
        }

        /**
         * @param string $table The unqualified name of a table
         * @return array<string,string> Map of (column => type); [] if not needed
         */
        protected function getValueTypesForWithClause( $table ) {
                return [];
        }

        public function deleteJoin(
                $delTable,
                $joinTable,
                $delVar,
                $joinVar,
                $conds,
                $fname = __METHOD__
        ) {
                $sql = $this->platform->deleteJoinSqlText( $delTable, $joinTable, $delVar, $joinVar, $conds );
                $query = new Query( $sql, self::QUERY_CHANGE_ROWS, 'DELETE', $delTable );
                $this->query( $query, $fname );
        }

        public function delete( $table, $conds, $fname = __METHOD__ ) {
                $this->query( $this->platform->deleteSqlText( $table, $conds ), $fname );

                return true;
        }

        final public function insertSelect(
                $destTable,
                $srcTable,
                $varMap,
                $conds,
                $fname = __METHOD__,
                $insertOptions = [],
                $selectOptions = [],
                $selectJoinConds = []
        ) {
                static $hints = [ 'NO_AUTO_COLUMNS' ];

                $insertOptions = $this->platform->normalizeOptions( $insertOptions );
                $selectOptions = $this->platform->normalizeOptions( $selectOptions );

                if ( $this->cliMode && $this->isInsertSelectSafe( $insertOptions, $selectOptions, $fname ) ) {
                        // For massive migrations with downtime, we don't want to select everything
                        // into memory and OOM, so do all this native on the server side if possible.
                        $this->doInsertSelectNative(
                                $destTable,
                                $srcTable,
                                $varMap,
                                $conds,
                                $fname,
                                array_diff( $insertOptions, $hints ),
                                $selectOptions,
                                $selectJoinConds
                        );
                } else {
                        $this->doInsertSelectGeneric(
                                $destTable,
                                $srcTable,
                                $varMap,
                                $conds,
                                $fname,
                                array_diff( $insertOptions, $hints ),
                                $selectOptions,
                                $selectJoinConds
                        );
                }

                return true;
        }

        /**
         * @param array $insertOptions
         * @param array $selectOptions
         * @param string $fname
         * @return bool Whether an INSERT SELECT with these options will be replication safe
         * @since 1.31
         */
        protected function isInsertSelectSafe( array $insertOptions, array $selectOptions, $fname ) {
                return true;
        }

        /**
         * Implementation of insertSelect() based on select() and insert()
         *
         * @see IDatabase::insertSelect()
         * @param string $destTable Unqualified name of destination table
         * @param string|array $srcTable Unqualified name of source table
         * @param array $varMap
         * @param array $conds
         * @param string $fname
         * @param array $insertOptions
         * @param array $selectOptions
         * @param array $selectJoinConds
         * @since 1.35
         */
        private function doInsertSelectGeneric(
                $destTable,
                $srcTable,
                array $varMap,
                $conds,
                $fname,
                array $insertOptions,
                array $selectOptions,
                $selectJoinConds
        ) {
                // For web requests, do a locking SELECT and then INSERT. This puts the SELECT burden
                // on only the primary DB (without needing row-based-replication). It also makes it easy to
                // know how big the INSERT is going to be.
                $fields = [];
                foreach ( $varMap as $dstColumn => $sourceColumnOrSql ) {
                        $fields[] = $this->platform->fieldNameWithAlias( $sourceColumnOrSql, $dstColumn );
                }
                $res = $this->select(
                        $srcTable,
                        implode( ',', $fields ),
                        $conds,
                        $fname,
                        array_merge( $selectOptions, [ 'FOR UPDATE' ] ),
                        $selectJoinConds
                );

                $affectedRowCount = 0;
                $insertId = null;
                if ( $res ) {
                        $this->startAtomic( $fname, self::ATOMIC_CANCELABLE );
                        try {
                                $rows = [];
                                foreach ( $res as $row ) {
                                        $rows[] = (array)$row;
                                }
                                // Avoid inserts that are too huge
                                $rowBatches = array_chunk( $rows, $this->nonNativeInsertSelectBatchSize );
                                foreach ( $rowBatches as $rows ) {
                                        $query = $this->platform->dispatchingInsertSqlText( $destTable, $rows, $insertOptions );
                                        $this->query( $query, $fname );
                                        $affectedRowCount += $this->lastQueryAffectedRows;
                                        $insertId = $insertId ?: $this->lastQueryInsertId;
                                }
                                $this->endAtomic( $fname );
                        } catch ( DBError $e ) {
                                $this->cancelAtomic( $fname );
                                throw $e;
                        }
                }
                $this->lastEmulatedAffectedRows = $affectedRowCount;
                $this->lastEmulatedInsertId = $insertId;
        }

        /**
         * Native server-side implementation of insertSelect() for situations where
         * we don't want to select everything into memory
         *
         * @see IDatabase::insertSelect()
         * @param string $destTable The unqualified name of destination table
         * @param string|array $srcTable The unqualified name of source table
         * @param array $varMap
         * @param array $conds
         * @param string $fname
         * @param array $insertOptions
         * @param array $selectOptions
         * @param array $selectJoinConds
         * @since 1.35
         */
        protected function doInsertSelectNative(
                $destTable,
                $srcTable,
                array $varMap,
                $conds,
                $fname,
                array $insertOptions,
                array $selectOptions,
                $selectJoinConds
        ) {
                $sql = $this->platform->insertSelectNativeSqlText(
                        $destTable,
                        $srcTable,
                        $varMap,
                        $conds,
                        $fname,
                        $insertOptions,
                        $selectOptions,
                        $selectJoinConds
                );
                $query = new Query(
                        $sql,
                        self::QUERY_CHANGE_ROWS,
                        'INSERT',
                        $destTable
                );
                $this->query( $query, $fname );
        }

        /**
         * Do not use this method outside of Database/DBError classes
         *
         * @param int|string $errno
         * @return bool Whether the given query error was a connection drop
         * @since 1.38
         */
        protected function isConnectionError( $errno ) {
                return false;
        }

        /**
         * @param int|string $errno
         * @return bool Whether it is known that the last query error only caused statement rollback
         * @note This is for backwards compatibility for callers catching DBError exceptions in
         *   order to ignore problems like duplicate key errors or foreign key violations
         * @since 1.39
         */
        protected function isKnownStatementRollbackError( $errno ) {
                return false; // don't know; it could have caused a transaction rollback
        }

        /**
         * @inheritDoc
         */
        public function serverIsReadOnly() {
                return false;
        }

        final public function onTransactionResolution( callable $callback, $fname = __METHOD__ ) {
                $this->transactionManager->onTransactionResolution( $this, $callback, $fname );
        }

        final public function onTransactionCommitOrIdle( callable $callback, $fname = __METHOD__ ) {
                if ( !$this->trxLevel() && $this->getTransactionRoundFname() !== null ) {
                        // This DB handle is set to participate in LoadBalancer transaction rounds and
                        // an explicit transaction round is active. Start an implicit transaction on this
                        // DB handle (setting trxAutomatic) similar to how query() does in such situations.
                        $this->begin( __METHOD__, self::TRANSACTION_INTERNAL );
                }

                $this->transactionManager->addPostCommitOrIdleCallback( $callback, $fname );
                if ( !$this->trxLevel() ) {
                        $dbErrors = [];
                        $this->runOnTransactionIdleCallbacks( self::TRIGGER_IDLE, $dbErrors );
                        if ( $dbErrors ) {
                                throw $dbErrors[0];
                        }
                }
        }

        final public function onTransactionPreCommitOrIdle( callable $callback, $fname = __METHOD__ ) {
                if ( !$this->trxLevel() && $this->getTransactionRoundFname() !== null ) {
                        // This DB handle is set to participate in LoadBalancer transaction rounds and
                        // an explicit transaction round is active. Start an implicit transaction on this
                        // DB handle (setting trxAutomatic) similar to how query() does in such situations.
                        $this->begin( __METHOD__, self::TRANSACTION_INTERNAL );
                }

                if ( $this->trxLevel() ) {
                        $this->transactionManager->addPreCommitOrIdleCallback(
                                $callback,
                                $fname
                        );
                } else {
                        // No transaction is active nor will start implicitly, so make one for this callback
                        $this->startAtomic( __METHOD__, self::ATOMIC_CANCELABLE );
                        try {
                                $callback( $this );
                        } catch ( Throwable $e ) {
                                // Avoid confusing error reporting during critical section errors
                                if ( !$this->csmError ) {
                                        $this->cancelAtomic( __METHOD__ );
                                }
                                throw $e;
                        }
                        $this->endAtomic( __METHOD__ );
                }
        }

        final public function setTransactionListener( $name, ?callable $callback = null ) {
                $this->transactionManager->setTransactionListener( $name, $callback );
        }

        /**
         * Whether to disable running of post-COMMIT/ROLLBACK callbacks
         *
         * @internal This method should not be used outside of Database/LoadBalancer
         *
         * @since 1.28
         * @param bool $suppress
         */
        final public function setTrxEndCallbackSuppression( $suppress ) {
                $this->transactionManager->setTrxEndCallbackSuppression( $suppress );
        }

        /**
         * Consume and run any "on transaction idle/resolution" callbacks
         *
         * @internal This method should not be used outside of Database/LoadBalancer
         *
         * @since 1.20
         * @param int $trigger IDatabase::TRIGGER_* constant
         * @param DBError[] &$errors DB exceptions caught [returned]
         * @return int Number of callbacks attempted
         * @throws DBUnexpectedError
         * @throws Throwable Any non-DBError exception thrown by a callback
         */
        public function runOnTransactionIdleCallbacks( $trigger, array &$errors = [] ) {
                if ( $this->trxLevel() ) {
                        throw new DBUnexpectedError( $this, __METHOD__ . ': a transaction is still open' );
                }

                if ( $this->transactionManager->isEndCallbacksSuppressed() ) {
                        // Execution deferred by LoadBalancer for explicit execution later
                        return 0;
                }

                $cs = $this->commenceCriticalSection( __METHOD__ );

                $count = 0;
                $autoTrx = $this->flagsHolder->hasImplicitTrxFlag(); // automatic begin() enabled?
                // Drain the queues of transaction "idle" and "end" callbacks until they are empty
                do {
                        $callbackEntries = $this->transactionManager->consumeEndCallbacks();
                        $count += count( $callbackEntries );
                        foreach ( $callbackEntries as $entry ) {
                                $this->flagsHolder->clearFlag( self::DBO_TRX ); // make each query its own transaction
                                try {
                                        $entry[0]( $trigger, $this );
                                } catch ( DBError $ex ) {
                                        call_user_func( $this->errorLogger, $ex );
                                        $errors[] = $ex;
                                        // Some callbacks may use startAtomic/endAtomic, so make sure
                                        // their transactions are ended so other callbacks don't fail
                                        if ( $this->trxLevel() ) {
                                                $this->rollback( __METHOD__, self::FLUSHING_INTERNAL );
                                        }
                                } finally {
                                        if ( $autoTrx ) {
                                                $this->flagsHolder->setFlag( self::DBO_TRX ); // restore automatic begin()
                                        } else {
                                                $this->flagsHolder->clearFlag( self::DBO_TRX ); // restore auto-commit
                                        }
                                }
                        }
                } while ( $this->transactionManager->countPostCommitOrIdleCallbacks() );

                $this->completeCriticalSection( __METHOD__, $cs );

                return $count;
        }

        /**
         * Actually run any "transaction listener" callbacks
         *
         * @internal This method should not be used outside of Database/LoadBalancer
         *
         * @since 1.20
         * @param int $trigger IDatabase::TRIGGER_* constant
         * @param DBError[] &$errors DB exceptions caught [returned]
         * @throws Throwable Any non-DBError exception thrown by a callback
         */
        public function runTransactionListenerCallbacks( $trigger, array &$errors = [] ) {
                if ( $this->transactionManager->isEndCallbacksSuppressed() ) {
                        // Execution deferred by LoadBalancer for explicit execution later
                        return;
                }

                // These callbacks should only be registered in setup, thus no iteration is needed
                foreach ( $this->transactionManager->getRecurringCallbacks() as $callback ) {
                        try {
                                $callback( $trigger, $this );
                        } catch ( DBError $ex ) {
                                ( $this->errorLogger )( $ex );
                                $errors[] = $ex;
                        }
                }
        }

        /**
         * Handle "on transaction idle/resolution" and "transaction listener" callbacks post-COMMIT
         *
         * @throws DBError The first DBError exception thrown by a callback
         * @throws Throwable Any non-DBError exception thrown by a callback
         */
        private function runTransactionPostCommitCallbacks() {
                $dbErrors = [];
                $this->runOnTransactionIdleCallbacks( self::TRIGGER_COMMIT, $dbErrors );
                $this->runTransactionListenerCallbacks( self::TRIGGER_COMMIT, $dbErrors );
                $this->lastEmulatedAffectedRows = 0; // for the sake of consistency
                if ( $dbErrors ) {
                        throw $dbErrors[0];
                }
        }

        /**
         * Handle "on transaction idle/resolution" and "transaction listener" callbacks post-ROLLBACK
         *
         * This will suppress and log any DBError exceptions
         *
         * @throws Throwable Any non-DBError exception thrown by a callback
         */
        private function runTransactionPostRollbackCallbacks() {
                $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
                $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );
                $this->lastEmulatedAffectedRows = 0; // for the sake of consistency
        }

        final public function startAtomic(
                $fname = __METHOD__,
                $cancelable = self::ATOMIC_NOT_CANCELABLE
        ) {
                $cs = $this->commenceCriticalSection( __METHOD__ );

                if ( $this->trxLevel() ) {
                        // This atomic section is only one part of a larger transaction
                        $sectionOwnsTrx = false;
                } else {
                        // Start an implicit transaction (sets trxAutomatic)
                        try {
                                $this->begin( $fname, self::TRANSACTION_INTERNAL );
                        } catch ( DBError $e ) {
                                $this->completeCriticalSection( __METHOD__, $cs );
                                throw $e;
                        }
                        if ( $this->flagsHolder->hasImplicitTrxFlag() ) {
                                // This DB handle participates in LoadBalancer transaction rounds; all atomic
                                // sections should be buffered into one transaction (e.g. to keep web requests
                                // transactional). Note that an implicit transaction round is considered to be
                                // active when no there is no explicit transaction round.
                                $sectionOwnsTrx = false;
                        } else {
                                // This DB handle does not participate in LoadBalancer transaction rounds;
                                // each topmost atomic section will use its own transaction.
                                $sectionOwnsTrx = true;
                        }
                        $this->transactionManager->setAutomaticAtomic( $sectionOwnsTrx );
                }

                if ( $cancelable === self::ATOMIC_CANCELABLE ) {
                        if ( $sectionOwnsTrx ) {
                                // This atomic section is synonymous with the whole transaction; just
                                // use full COMMIT/ROLLBACK in endAtomic()/cancelAtomic(), respectively
                                $savepointId = self::NOT_APPLICABLE;
                        } else {
                                // This atomic section is only part of the whole transaction; use a SAVEPOINT
                                // query so that its changes can be cancelled without losing the rest of the
                                // transaction (e.g. changes from other sections or from outside of sections)
                                try {
                                        $savepointId = $this->transactionManager->nextSavePointId( $this, $fname );
                                        $sql = $this->platform->savepointSqlText( $savepointId );
                                        $query = new Query( $sql, self::QUERY_CHANGE_TRX, 'SAVEPOINT' );
                                        $this->query( $query, $fname );
                                } catch ( DBError $e ) {
                                        $this->completeCriticalSection( __METHOD__, $cs, $e );
                                        throw $e;
                                }
                        }
                } else {
                        $savepointId = null;
                }

                $sectionId = new AtomicSectionIdentifier;
                $this->transactionManager->addToAtomicLevels( $fname, $sectionId, $savepointId );

                $this->completeCriticalSection( __METHOD__, $cs );

                return $sectionId;
        }

        final public function endAtomic( $fname = __METHOD__ ) {
                [ $savepointId, $sectionId ] = $this->transactionManager->onEndAtomic( $this, $fname );

                $runPostCommitCallbacks = false;

                $cs = $this->commenceCriticalSection( __METHOD__ );

                // Remove the last section (no need to re-index the array)
                $finalLevelOfImplicitTrxPopped = $this->transactionManager->popAtomicLevel();

                try {
                        if ( $finalLevelOfImplicitTrxPopped ) {
                                $this->commit( $fname, self::FLUSHING_INTERNAL );
                                $runPostCommitCallbacks = true;
                        } elseif ( $savepointId !== null && $savepointId !== self::NOT_APPLICABLE ) {
                                $sql = $this->platform->releaseSavepointSqlText( $savepointId );
                                $query = new Query( $sql, self::QUERY_CHANGE_TRX, 'RELEASE SAVEPOINT' );
                                $this->query( $query, $fname );
                        }
                } catch ( DBError $e ) {
                        $this->completeCriticalSection( __METHOD__, $cs, $e );
                        throw $e;
                }

                $this->transactionManager->onEndAtomicInCriticalSection( $sectionId );

                $this->completeCriticalSection( __METHOD__, $cs );

                if ( $runPostCommitCallbacks ) {
                        $this->runTransactionPostCommitCallbacks();
                }
        }

        final public function cancelAtomic(
                $fname = __METHOD__,
                ?AtomicSectionIdentifier $sectionId = null
        ) {
                $this->transactionManager->onCancelAtomicBeforeCriticalSection( $this, $fname );
                $pos = $this->transactionManager->getPositionFromSectionId( $sectionId );
                if ( $pos < 0 ) {
                        throw new DBUnexpectedError( $this, "Atomic section not found (for $fname)" );
                }

                $cs = $this->commenceCriticalSection( __METHOD__ );
                $runPostRollbackCallbacks = false;
                [ $savedFname, $excisedSectionIds, $newTopSectionId, $savedSectionId, $savepointId ] =
                        $this->transactionManager->cancelAtomic( $pos );

                try {
                        if ( $savedFname !== $fname ) {
                                $e = new DBUnexpectedError(
                                        $this,
                                        "Invalid atomic section ended (got $fname but expected $savedFname)"
                                );
                                $this->completeCriticalSection( __METHOD__, $cs, $e );
                                throw $e;
                        }

                        // Remove the last section (no need to re-index the array)
                        $this->transactionManager->popAtomicLevel();
                        $excisedSectionIds[] = $savedSectionId;
                        $newTopSectionId = $this->transactionManager->currentAtomicSectionId();

                        if ( $savepointId !== null ) {
                                // Rollback the transaction changes proposed within this atomic section
                                if ( $savepointId === self::NOT_APPLICABLE ) {
                                        // Atomic section started the transaction; rollback the whole transaction
                                        // and trigger cancellation callbacks for all active atomic sections
                                        $this->rollback( $fname, self::FLUSHING_INTERNAL );
                                        $runPostRollbackCallbacks = true;
                                } else {
                                        // Atomic section nested within the transaction; rollback the transaction
                                        // to the state prior to this section and trigger its cancellation callbacks
                                        $sql = $this->platform->rollbackToSavepointSqlText( $savepointId );
                                        $query = new Query( $sql, self::QUERY_CHANGE_TRX, 'ROLLBACK TO SAVEPOINT' );
                                        $this->query( $query, $fname );
                                        $this->transactionManager->setTrxStatusToOk(); // no exception; recovered
                                }
                        } else {
                                // Put the transaction into an error state if it's not already in one
                                $trxError = new DBUnexpectedError(
                                        $this,
                                        "Uncancelable atomic section canceled (got $fname)"
                                );
                                $this->transactionManager->setTransactionError( $trxError );
                        }
                } finally {
                        // Fix up callbacks owned by the sections that were just cancelled.
                        // All callbacks should have an owner that is present in trxAtomicLevels.
                        $this->transactionManager->modifyCallbacksForCancel(
                                $excisedSectionIds,
                                $newTopSectionId
                        );
                }

                $this->lastEmulatedAffectedRows = 0; // for the sake of consistency

                $this->completeCriticalSection( __METHOD__, $cs );

                if ( $runPostRollbackCallbacks ) {
                        $this->runTransactionPostRollbackCallbacks();
                }
        }

        final public function doAtomicSection(
                $fname,
                callable $callback,
                $cancelable = self::ATOMIC_NOT_CANCELABLE
        ) {
                $sectionId = $this->startAtomic( $fname, $cancelable );
                try {
                        $res = $callback( $this, $fname );
                } catch ( Throwable $e ) {
                        // Avoid confusing error reporting during critical section errors
                        if ( !$this->csmError ) {
                                $this->cancelAtomic( $fname, $sectionId );
                        }

                        throw $e;
                }
                $this->endAtomic( $fname );

                return $res;
        }

        final public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT ) {
                static $modes = [ self::TRANSACTION_EXPLICIT, self::TRANSACTION_INTERNAL ];
                if ( !in_array( $mode, $modes, true ) ) {
                        throw new DBUnexpectedError( $this, "$fname: invalid mode parameter '$mode'" );
                }

                $this->transactionManager->onBegin( $this, $fname );

                if ( $this->flagsHolder->hasImplicitTrxFlag() && $mode !== self::TRANSACTION_INTERNAL ) {
                        $msg = "$fname: implicit transaction expected (DBO_TRX set)";
                        throw new DBUnexpectedError( $this, $msg );
                }

                $this->assertHasConnectionHandle();

                $cs = $this->commenceCriticalSection( __METHOD__ );
                $timeStart = microtime( true );
                try {
                        $this->doBegin( $fname );
                } catch ( DBError $e ) {
                        $this->completeCriticalSection( __METHOD__, $cs );
                        throw $e;
                }
                $timeEnd = microtime( true );
                // Treat "BEGIN" as a trivial query to gauge the RTT delay
                $rtt = max( $timeEnd - $timeStart, 0.0 );
                $this->transactionManager->onBeginInCriticalSection( $mode, $fname, $rtt );
                $this->replicationReporter->resetReplicationLagStatus( $this );
                $this->completeCriticalSection( __METHOD__, $cs );
        }

        /**
         * Issues the BEGIN command to the database server.
         *
         * @see Database::begin()
         * @param string $fname
         * @throws DBError
         */
        protected function doBegin( $fname ) {
                $query = new Query( 'BEGIN', self::QUERY_CHANGE_TRX, 'BEGIN' );
                $this->query( $query, $fname );
        }

        final public function commit( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
                static $modes = [ self::FLUSHING_ONE, self::FLUSHING_ALL_PEERS, self::FLUSHING_INTERNAL ];
                if ( !in_array( $flush, $modes, true ) ) {
                        throw new DBUnexpectedError( $this, "$fname: invalid flush parameter '$flush'" );
                }

                if ( !$this->transactionManager->onCommit( $this, $fname, $flush ) ) {
                        return;
                }

                $this->assertHasConnectionHandle();

                $this->runOnTransactionPreCommitCallbacks();

                $cs = $this->commenceCriticalSection( __METHOD__ );
                try {
                        if ( $this->trxLevel() ) {
                                $query = new Query( 'COMMIT', self::QUERY_CHANGE_TRX, 'COMMIT' );
                                $this->query( $query, $fname );
                        }
                } catch ( DBError $e ) {
                        $this->completeCriticalSection( __METHOD__, $cs );
                        throw $e;
                }
                $lastWriteTime = $this->transactionManager->onCommitInCriticalSection( $this );
                if ( $lastWriteTime ) {
                        $this->lastWriteTime = $lastWriteTime;
                }
                // With FLUSHING_ALL_PEERS, callbacks will run when requested by a dedicated phase
                // within LoadBalancer. With FLUSHING_INTERNAL, callbacks will run when requested by
                // the Database caller during a safe point. This avoids isolation and recursion issues.
                if ( $flush === self::FLUSHING_ONE ) {
                        $this->runTransactionPostCommitCallbacks();
                }
                $this->completeCriticalSection( __METHOD__, $cs );
        }

        final public function rollback( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
                if (
                        $flush !== self::FLUSHING_INTERNAL &&
                        $flush !== self::FLUSHING_ALL_PEERS &&
                        $this->flagsHolder->hasImplicitTrxFlag()
                ) {
                        throw new DBUnexpectedError(
                                $this,
                                "$fname: Expected mass rollback of all peer transactions (DBO_TRX set)"
                        );
                }

                if ( !$this->trxLevel() ) {
                        $this->transactionManager->setTrxStatusToNone();
                        $this->transactionManager->clearPreEndCallbacks();
                        if ( $this->transactionManager->trxLevel() === TransactionManager::STATUS_TRX_ERROR ) {
                                $this->logger->info(
                                        "$fname: acknowledged server-side transaction loss on {db_server}",
                                        $this->getLogContext()
                                );
                        }

                        return;
                }

                $this->assertHasConnectionHandle();

                if ( $this->csmError ) {
                        // Since the session state is corrupt, we cannot just rollback the transaction
                        // while preserving the non-transaction session state. The handle will remain
                        // marked as corrupt until flushSession() is called to reset the connection
                        // and deal with any remaining callbacks.
                        $this->logger->info(
                                "$fname: acknowledged client-side transaction loss on {db_server}",
                                $this->getLogContext()
                        );

                        return;
                }

                $cs = $this->commenceCriticalSection( __METHOD__ );
                if ( $this->trxLevel() ) {
                        // Disconnects cause rollback anyway, so ignore those errors
                        $query = new Query(
                                $this->platform->rollbackSqlText(),
                                self::QUERY_SILENCE_ERRORS | self::QUERY_CHANGE_TRX,
                                'ROLLBACK'
                        );
                        $this->query( $query, $fname );
                }
                $this->transactionManager->onRollbackInCriticalSection( $this );
                // With FLUSHING_ALL_PEERS, callbacks will run when requested by a dedicated phase
                // within LoadBalancer. With FLUSHING_INTERNAL, callbacks will run when requested by
                // the Database caller during a safe point. This avoids isolation and recursion issues.
                if ( $flush === self::FLUSHING_ONE ) {
                        $this->runTransactionPostRollbackCallbacks();
                }
                $this->completeCriticalSection( __METHOD__, $cs );
        }

        /**
         * @internal Only for tests and highly discouraged
         * @param TransactionManager $transactionManager
         */
        public function setTransactionManager( TransactionManager $transactionManager ) {
                $this->transactionManager = $transactionManager;
        }

        public function flushSession( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
                if (
                        $flush !== self::FLUSHING_INTERNAL &&
                        $flush !== self::FLUSHING_ALL_PEERS &&
                        $this->flagsHolder->hasImplicitTrxFlag()
                ) {
                        throw new DBUnexpectedError(
                                $this,
                                "$fname: Expected mass flush of all peer connections (DBO_TRX set)"
                        );
                }

                if ( $this->csmError ) {
                        // If a critical section error occurred, such as Excimer timeout exceptions raised
                        // before a query response was marshalled, destroy the connection handle and reset
                        // the session state tracking variables. The value of trxLevel() is irrelevant here,
                        // and, in fact, might be 1 due to rollback() deferring critical section recovery.
                        $this->logger->info(
                                "$fname: acknowledged client-side session loss on {db_server}",
                                $this->getLogContext()
                        );
                        $this->csmError = null;
                        $this->csmFname = null;
                        $this->replaceLostConnection( 2048, __METHOD__ );

                        return;
                }

                if ( $this->trxLevel() ) {
                        // Any existing transaction should have been rolled back already
                        throw new DBUnexpectedError(
                                $this,
                                "$fname: transaction still in progress (not yet rolled back)"
                        );
                }

                if ( $this->transactionManager->sessionStatus() === TransactionManager::STATUS_SESS_ERROR ) {
                        // If the session state was already lost due to either an unacknowledged session
                        // state loss error (e.g. dropped connection) or an explicit connection close call,
                        // then there is nothing to do here. Note that in such cases, even temporary tables
                        // and server-side config variables are lost (invocation of this method is assumed
                        // to imply that such losses are tolerable).
                        $this->logger->info(
                                "$fname: acknowledged server-side session loss on {db_server}",
                                $this->getLogContext()
                        );
                } elseif ( $this->isOpen() ) {
                        // Connection handle exists; server-side session state must be flushed
                        $this->doFlushSession( $fname );
                        $this->sessionNamedLocks = [];
                }

                $this->transactionManager->clearSessionError();
        }

        /**
         * Reset the server-side session state for named locks and table locks
         *
         * Connection and query errors will be suppressed and logged
         *
         * @param string $fname
         * @since 1.38
         */
        protected function doFlushSession( $fname ) {
                // no-op
        }

        public function flushSnapshot( $fname = __METHOD__, $flush = self::FLUSHING_ONE ) {
                $this->transactionManager->onFlushSnapshot(
                        $this,
                        $fname,
                        $flush,
                        $this->getTransactionRoundFname()
                );
                if (
                        $this->transactionManager->sessionStatus() === TransactionManager::STATUS_SESS_ERROR ||
                        $this->transactionManager->trxStatus() === TransactionManager::STATUS_TRX_ERROR
                ) {
                        $this->rollback( $fname, self::FLUSHING_INTERNAL );
                } else {
                        $this->commit( $fname, self::FLUSHING_INTERNAL );
                }
        }

        public function duplicateTableStructure(
                $oldName,
                $newName,
                $temporary = false,
                $fname = __METHOD__
        ) {
                throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
        }

        public function listTables( $prefix = null, $fname = __METHOD__ ) {
                throw new RuntimeException( __METHOD__ . ' is not implemented in descendant class' );
        }

        public function affectedRows() {
                $this->lastEmulatedAffectedRows ??= $this->lastQueryAffectedRows;

                return $this->lastEmulatedAffectedRows;
        }

        public function insertId() {
                if ( $this->lastEmulatedInsertId === null ) {
                        // Guard against misuse of this method by checking affectedRows(). Note that calls
                        // to insert() with "IGNORE" and calls to insertSelect() might not add any rows.
                        if ( $this->affectedRows() ) {
                                $this->lastEmulatedInsertId = $this->lastInsertId();
                        } else {
                                $this->lastEmulatedInsertId = 0;
                        }
                }

                return $this->lastEmulatedInsertId;
        }

        /**
         * Get a row ID from the last insert statement to implicitly assign one within the session
         *
         * If the statement involved assigning sequence IDs to multiple rows, then the return value
         * will be any one of those values (database-specific). If the statement was an "UPSERT" and
         * some existing rows were updated, then the result will either reflect only IDs of created
         * rows or it will reflect IDs of both created and updated rows (this is database-specific).
         *
         * The result is unspecified if the statement gave an error.
         *
         * @return int Sequence ID, 0 (if none)
         * @throws DBError
         */
        abstract protected function lastInsertId();

        public function ping() {
                if ( $this->isOpen() ) {
                        // If the connection was recently used, assume that it is still good
                        if ( ( microtime( true ) - $this->lastPing ) < self::PING_TTL ) {
                                return true;
                        }
                        // Send a trivial query to test the connection, triggering an automatic
                        // reconnection attempt if the connection was lost
                        $query = new Query(
                                self::PING_QUERY,
                                self::QUERY_IGNORE_DBO_TRX | self::QUERY_SILENCE_ERRORS | self::QUERY_CHANGE_NONE,
                                'SELECT'
                        );
                        $res = $this->query( $query, __METHOD__ );
                        $ok = ( $res !== false );
                } else {
                        // Try to re-establish a connection
                        $ok = $this->replaceLostConnection( null, __METHOD__ );
                }

                return $ok;
        }

        /**
         * Close any existing (dead) database connection and open a new connection
         *
         * @param int|null $lastErrno
         * @param string $fname
         * @return bool True if new connection is opened successfully, false if error
         */
        protected function replaceLostConnection( $lastErrno, $fname ) {
                if ( $this->conn ) {
                        $this->closeConnection();
                        $this->conn = null;
                        $this->handleSessionLossPreconnect();
                }

                try {
                        $this->open(
                                $this->connectionParams[self::CONN_HOST],
                                $this->connectionParams[self::CONN_USER],
                                $this->connectionParams[self::CONN_PASSWORD],
                                $this->currentDomain->getDatabase(),
                                $this->currentDomain->getSchema(),
                                $this->tablePrefix()
                        );
                        $this->lastPing = microtime( true );
                        $ok = true;

                        $this->logger->warning(
                                $fname . ': lost connection to {db_server} with error {errno}; reconnected',
                                $this->getLogContext( [
                                        'exception' => new RuntimeException(),
                                        'db_log_category' => 'connection',
                                        'errno' => $lastErrno
                                ] )
                        );
                } catch ( DBConnectionError $e ) {
                        $ok = false;

                        $this->logger->error(
                                $fname . ': lost connection to {db_server} with error {errno}; reconnection failed: {connect_msg}',
                                $this->getLogContext( [
                                        'exception' => new RuntimeException(),
                                        'db_log_category' => 'connection',
                                        'errno' => $lastErrno,
                                        'connect_msg' => $e->getMessage()
                                ] )
                        );
                }

                // Handle callbacks in trxEndCallbacks, e.g. onTransactionResolution().
                // If callback suppression is set then the array will remain unhandled.
                $this->runOnTransactionIdleCallbacks( self::TRIGGER_ROLLBACK );
                // Handle callbacks in trxRecurringCallbacks, e.g. setTransactionListener().
                // If callback suppression is set then the array will remain unhandled.
                $this->runTransactionListenerCallbacks( self::TRIGGER_ROLLBACK );

                return $ok;
        }

        /**
         * Merge the result of getSessionLagStatus() for several DBs
         * using the most pessimistic values to estimate the lag of
         * any data derived from them in combination
         *
         * This is information is useful for caching modules
         *
         * @see WANObjectCache::set()
         * @see WANObjectCache::getWithSetCallback()
         *
         * @param IReadableDatabase|null ...$dbs
         * Note: For backward compatibility, it is allowed for null values
         * to be passed among the parameters. This is deprecated since 1.36,
         * only IReadableDatabase objects should be passed.
         *
         * @return array Map of values:
         *   - lag: highest lag of any of the DBs or false on error (e.g. replication stopped)
         *   - since: oldest UNIX timestamp of any of the DB lag estimates
         *   - pending: whether any of the DBs have uncommitted changes
         * @throws DBError
         * @since 1.27
         */
        public static function getCacheSetOptions( ?IReadableDatabase ...$dbs ) {
                $res = [ 'lag' => 0, 'since' => INF, 'pending' => false ];

                foreach ( func_get_args() as $db ) {
                        if ( $db instanceof IReadableDatabase ) {
                                $status = $db->getSessionLagStatus();

                                if ( $status['lag'] === false ) {
                                        $res['lag'] = false;
                                } elseif ( $res['lag'] !== false ) {
                                        $res['lag'] = max( $res['lag'], $status['lag'] );
                                }
                                $res['since'] = min( $res['since'], $status['since'] );
                        }

                        if ( $db instanceof IDatabaseForOwner ) {
                                $res['pending'] = $res['pending'] ?: $db->writesPending();
                        }
                }

                return $res;
        }

        public function encodeBlob( $b ) {
                return $b;
        }

        public function decodeBlob( $b ) {
                if ( $b instanceof Blob ) {
                        $b = $b->fetch();
                }
                return $b;
        }

        public function setSessionOptions( array $options ) {
        }

        public function sourceFile(
                $filename,
                ?callable $lineCallback = null,
                ?callable $resultCallback = null,
                $fname = false,
                ?callable $inputCallback = null
        ) {
                AtEase::suppressWarnings();
                $fp = fopen( $filename, 'r' );
                AtEase::restoreWarnings();

                if ( $fp === false ) {
                        throw new RuntimeException( "Could not open \"{$filename}\"" );
                }

                if ( !$fname ) {
                        $fname = __METHOD__ . "( $filename )";
                }

                try {
                        return $this->sourceStream(
                                $fp,
                                $lineCallback,
                                $resultCallback,
                                $fname,
                                $inputCallback
                        );
                } finally {
                        fclose( $fp );
                }
        }

        public function sourceStream(
                $fp,
                ?callable $lineCallback = null,
                ?callable $resultCallback = null,
                $fname = __METHOD__,
                ?callable $inputCallback = null
        ) {
                $delimiterReset = new ScopedCallback(
                        function ( $delimiter ) {
                                $this->delimiter = $delimiter;
                        },
                        [ $this->delimiter ]
                );
                $cmd = '';

                while ( !feof( $fp ) ) {
                        if ( $lineCallback ) {
                                call_user_func( $lineCallback );
                        }

                        $line = trim( fgets( $fp ) );

                        if ( $line == '' ) {
                                continue;
                        }

                        if ( $line[0] == '-' && $line[1] == '-' ) {
                                continue;
                        }

                        if ( $cmd != '' ) {
                                $cmd .= ' ';
                        }

                        $done = $this->streamStatementEnd( $cmd, $line );

                        $cmd .= "$line\n";

                        if ( $done || feof( $fp ) ) {
                                $cmd = $this->platform->replaceVars( $cmd );

                                if ( $inputCallback ) {
                                        $callbackResult = $inputCallback( $cmd );

                                        if ( is_string( $callbackResult ) || !$callbackResult ) {
                                                $cmd = $callbackResult;
                                        }
                                }

                                if ( $cmd ) {
                                        $res = $this->query( $cmd, $fname );

                                        if ( $resultCallback ) {
                                                $resultCallback( $res, $this );
                                        }

                                        if ( $res === false ) {
                                                $err = $this->lastError();

                                                return "Query \"{$cmd}\" failed with error code \"$err\".\n";
                                        }
                                }
                                $cmd = '';
                        }
                }

                ScopedCallback::consume( $delimiterReset );
                return true;
        }

        /**
         * Called by sourceStream() to check if we've reached a statement end
         *
         * @param string &$sql SQL assembled so far
         * @param string &$newLine New line about to be added to $sql
         * @return bool Whether $newLine contains end of the statement
         */
        public function streamStatementEnd( &$sql, &$newLine ) {
                if ( $this->delimiter ) {
                        $prev = $newLine;
                        $newLine = preg_replace(
                                '/' . preg_quote( $this->delimiter, '/' ) . '$/',
                                '',
                                $newLine
                        );
                        if ( $newLine != $prev ) {
                                return true;
                        }
                }

                return false;
        }

        /**
         * @inheritDoc
         */
        public function lockIsFree( $lockName, $method ) {
                // RDBMs methods for checking named locks may or may not count this thread itself.
                // In MySQL, IS_FREE_LOCK() returns 0 if the thread already has the lock. This is
                // the behavior chosen by the interface for this method.
                if ( isset( $this->sessionNamedLocks[$lockName] ) ) {
                        $lockIsFree = false;
                } else {
                        $lockIsFree = $this->doLockIsFree( $lockName, $method );
                }

                return $lockIsFree;
        }

        /**
         * @see lockIsFree()
         *
         * @param string $lockName
         * @param string $method
         * @return bool Success
         * @throws DBError
         */
        protected function doLockIsFree( string $lockName, string $method ) {
                return true; // not implemented
        }

        /**
         * @inheritDoc
         */
        public function lock( $lockName, $method, $timeout = 5, $flags = 0 ) {
                $lockTsUnix = $this->doLock( $lockName, $method, $timeout );
                if ( $lockTsUnix !== null ) {
                        $locked = true;
                        $this->sessionNamedLocks[$lockName] = [
                                'ts' => $lockTsUnix,
                                'trxId' => $this->transactionManager->getTrxId()
                        ];
                } else {
                        $locked = false;
                        $this->logger->info(
                                __METHOD__ . ": failed to acquire lock '{lockname}'",
                                [
                                        'lockname' => $lockName,
                                        'db_log_category' => 'locking'
                                ]
                        );
                }

                return $this->flagsHolder::contains( $flags, self::LOCK_TIMESTAMP ) ? $lockTsUnix : $locked;
        }

        /**
         * @see lock()
         *
         * @param string $lockName
         * @param string $method
         * @param int $timeout
         * @return float|null UNIX timestamp of lock acquisition; null on failure
         * @throws DBError
         */
        protected function doLock( string $lockName, string $method, int $timeout ) {
                return microtime( true ); // not implemented
        }

        /**
         * @inheritDoc
         */
        public function unlock( $lockName, $method ) {
                if ( !isset( $this->sessionNamedLocks[$lockName] ) ) {
                        $released = false;
                        $this->logger->warning(
                                __METHOD__ . ": trying to release unheld lock '$lockName'\n",
                                [ 'db_log_category' => 'locking' ]
                        );
                } else {
                        $released = $this->doUnlock( $lockName, $method );
                        if ( $released ) {
                                unset( $this->sessionNamedLocks[$lockName] );
                        } else {
                                $this->logger->warning(
                                        __METHOD__ . ": failed to release lock '$lockName'\n",
                                        [ 'db_log_category' => 'locking' ]
                                );
                        }
                }

                return $released;
        }

        /**
         * @see unlock()
         *
         * @param string $lockName
         * @param string $method
         * @return bool Success
         * @throws DBError
         */
        protected function doUnlock( string $lockName, string $method ) {
                return true; // not implemented
        }

        public function getScopedLockAndFlush( $lockKey, $fname, $timeout ) {
                $this->transactionManager->onGetScopedLockAndFlush( $this, $fname );

                if ( !$this->lock( $lockKey, $fname, $timeout ) ) {
                        return null;
                }

                $unlocker = new ScopedCallback( function () use ( $lockKey, $fname ) {
                        // Note that the callback can be reached due to an exception making the calling
                        // function end early. If the transaction/session is in an error state, avoid log
                        // spam and confusing replacement of an original DBError with one about unlock().
                        // Unlock query will fail anyway; avoid possibly triggering errors in rollback()
                        if (
                                $this->transactionManager->sessionStatus() === TransactionManager::STATUS_SESS_ERROR ||
                                $this->transactionManager->trxStatus() === TransactionManager::STATUS_TRX_ERROR
                        ) {
                                return;
                        }
                        if ( $this->trxLevel() ) {
                                $this->onTransactionResolution(
                                        function () use ( $lockKey, $fname ) {
                                                $this->unlock( $lockKey, $fname );
                                        },
                                        $fname
                                );
                        } else {
                                $this->unlock( $lockKey, $fname );
                        }
                } );

                $this->commit( $fname, self::FLUSHING_INTERNAL );

                return $unlocker;
        }

        public function dropTable( $table, $fname = __METHOD__ ) {
                if ( !$this->tableExists( $table, $fname ) ) {
                        return false;
                }

                $query = new Query(
                        $this->platform->dropTableSqlText( $table ),
                        self::QUERY_CHANGE_SCHEMA,
                        'DROP',
                        $table
                );
                $this->query( $query, $fname );

                return true;
        }

        public function truncateTable( $table, $fname = __METHOD__ ) {
                $sql = "TRUNCATE TABLE " . $this->tableName( $table );
                $query = new Query( $sql, self::QUERY_CHANGE_SCHEMA, 'TRUNCATE', $table );
                $this->query( $query, $fname );
        }

        public function isReadOnly() {
                return ( $this->getReadOnlyReason() !== null );
        }

        /**
         * @return array|null Tuple of (reason string, "role" or "lb") if read-only; null otherwise
         */
        protected function getReadOnlyReason() {
                $reason = $this->replicationReporter->getTopologyBasedReadOnlyReason();
                if ( $reason ) {
                        return $reason;
                }

                $reason = $this->getLBInfo( self::LB_READ_ONLY_REASON );
                if ( is_string( $reason ) ) {
                        return [ $reason, 'lb' ];
                }

                return null;
        }

        /**
         * Get the underlying binding connection handle
         *
         * Makes sure the connection resource is set (disconnects and ping() failure can unset it).
         * This catches broken callers than catch and ignore disconnection exceptions.
         * Unlike checking isOpen(), this is safe to call inside of open().
         *
         * @return mixed
         * @throws DBUnexpectedError
         * @since 1.26
         */
        protected function getBindingHandle() {
                if ( !$this->conn ) {
                        throw new DBUnexpectedError(
                                $this,
                                'DB connection was already closed or the connection dropped'
                        );
                }

                return $this->conn;
        }

        /**
         * Demark the start of a critical section of session/transaction state changes
         *
         * Use this to disable potentially DB handles due to corruption from highly unexpected
         * exceptions (e.g. from zend timers or coding errors) preempting execution of methods.
         *
         * Callers must demark completion of the critical section with completeCriticalSection().
         * Callers should handle DBError exceptions that do not cause object state corruption by
         * catching them, calling completeCriticalSection(), and then rethrowing them.
         *
         * @code
         *     $cs = $this->commenceCriticalSection( __METHOD__ );
         *     try {
         *         //...send a query that changes the session/transaction state...
         *     } catch ( DBError $e ) {
         *         $this->completeCriticalSection( __METHOD__, $cs );
         *         throw $expectedException;
         *     }
         *     try {
         *         //...send another query that changes the session/transaction state...
         *     } catch ( DBError $trxError ) {
         *         // Require ROLLBACK before allowing any other queries from outside callers
         *         $this->completeCriticalSection( __METHOD__, $cs, $trxError );
         *         throw $expectedException;
         *     }
         *     // ...update session state fields of $this...
         *     $this->completeCriticalSection( __METHOD__, $cs );
         * @endcode
         *
         * @see Database::completeCriticalSection()
         *
         * @since 1.36
         * @param string $fname Caller name
         * @return CriticalSectionScope|null RAII-style monitor (topmost sections only)
         * @throws DBUnexpectedError If an unresolved critical section error already exists
         */
        protected function commenceCriticalSection( string $fname ) {
                if ( $this->csmError ) {
                        throw new DBUnexpectedError(
                                $this,
                                "Cannot execute $fname critical section while session state is out of sync.\n\n" .
                                $this->csmError->getMessage() . "\n" .
                                $this->csmError->getTraceAsString()
                        );
                }

                if ( $this->csmId ) {
                        $csm = null; // fold into the outer critical section
                } elseif ( $this->csProvider ) {
                        $csm = $this->csProvider->scopedEnter(
                                $fname,
                                null, // emergency limit (default)
                                null, // emergency callback (default)
                                function () use ( $fname ) {
                                        // Mark a critical section as having been aborted by an error
                                        $e = new RuntimeException( "A critical section from {$fname} has failed" );
                                        $this->csmError = $e;
                                        $this->csmId = null;
                                }
                        );
                        $this->csmId = $csm->getId();
                        $this->csmFname = $fname;
                } else {
                        $csm = null; // not supported
                }

                return $csm;
        }

        /**
         * Demark the completion of a critical section of session/transaction state changes
         *
         * @see Database::commenceCriticalSection()
         *
         * @since 1.36
         * @param string $fname Caller name
         * @param CriticalSectionScope|null $csm RAII-style monitor (topmost sections only)
         * @param Throwable|null $trxError Error that requires setting STATUS_TRX_ERROR (if any)
         */
        protected function completeCriticalSection(
                string $fname,
                ?CriticalSectionScope $csm,
                ?Throwable $trxError = null
        ) {
                if ( $csm !== null ) {
                        if ( $this->csmId === null ) {
                                throw new LogicException( "$fname critical section is not active" );
                        } elseif ( $csm->getId() !== $this->csmId ) {
                                throw new LogicException(
                                        "$fname critical section is not the active ({$this->csmFname}) one"
                                );
                        }

                        $csm->exit();
                        $this->csmId = null;
                }

                if ( $trxError ) {
                        $this->transactionManager->setTransactionError( $trxError );
                }
        }

        public function __toString() {
                $id = spl_object_id( $this );

                $description = $this->getType() . ' object #' . $id;
                // phpcs:ignore MediaWiki.Usage.ForbiddenFunctions.is_resource
                if ( is_resource( $this->conn ) ) {
                        $description .= ' (' . (string)$this->conn . ')'; // "resource id #<ID>"
                } elseif ( is_object( $this->conn ) ) {
                        $handleId = spl_object_id( $this->conn );
                        $description .= " (handle id #$handleId)";
                }

                return $description;
        }

        /**
         * Make sure that copies do not share the same client binding handle
         * @throws DBConnectionError
         */
        public function __clone() {
                $this->logger->warning(
                        "Cloning " . static::class . " is not recommended; forking connection",
                        [
                                'exception' => new RuntimeException(),
                                'db_log_category' => 'connection'
                        ]
                );

                if ( $this->isOpen() ) {
                        // Open a new connection resource without messing with the old one
                        $this->conn = null;
                        $this->transactionManager->clearEndCallbacks();
                        $this->handleSessionLossPreconnect(); // no trx or locks anymore
                        $this->open(
                                $this->connectionParams[self::CONN_HOST],
                                $this->connectionParams[self::CONN_USER],
                                $this->connectionParams[self::CONN_PASSWORD],
                                $this->currentDomain->getDatabase(),
                                $this->currentDomain->getSchema(),
                                $this->tablePrefix()
                        );
                        $this->lastPing = microtime( true );
                }
        }

        /**
         * Called by serialize. Throw an exception when DB connection is serialized.
         * This causes problems on some database engines because the connection is
         * not restored on unserialize.
         * @return never
         */
        public function __sleep() {
                throw new RuntimeException( 'Database serialization may cause problems, since ' .
                        'the connection is not restored on wakeup' );
        }

        /**
         * Run a few simple checks and close dangling connections
         */
        public function __destruct() {
                if ( $this->transactionManager ) {
                        // Tests mock this class and disable constructor.
                        $this->transactionManager->onDestruct();
                }

                $danglingWriters = $this->pendingWriteAndCallbackCallers();
                if ( $danglingWriters ) {
                        $fnames = implode( ', ', $danglingWriters );
                        trigger_error( "DB transaction writes or callbacks still pending ($fnames)" );
                }

                if ( $this->conn ) {
                        // Avoid connection leaks. Normally, resources close at script completion.
                        // The connection might already be closed in PHP by now, so suppress warnings.
                        AtEase::suppressWarnings();
                        $this->closeConnection();
                        AtEase::restoreWarnings();
                        $this->conn = null;
                }
        }

        /* Start of methods delegated to DatabaseFlags. Avoid using them outside of rdbms library */

        public function setFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
                $this->flagsHolder->setFlag( $flag, $remember );
        }

        public function clearFlag( $flag, $remember = self::REMEMBER_NOTHING ) {
                $this->flagsHolder->clearFlag( $flag, $remember );
        }

        public function restoreFlags( $state = self::RESTORE_PRIOR ) {
                $this->flagsHolder->restoreFlags( $state );
        }

        public function getFlag( $flag ) {
                return $this->flagsHolder->getFlag( $flag );
        }

        /* End of methods delegated to DatabaseFlags. */

        /* Start of methods delegated to TransactionManager. Avoid using them outside of rdbms library */

        final public function trxLevel() {
                // FIXME: A lot of tests disable constructor leading to trx manager being
                // null and breaking, this is unacceptable but hopefully this should
                // happen less by moving these functions to the transaction manager class.
                if ( !$this->transactionManager ) {
                        $this->transactionManager = new TransactionManager( new NullLogger() );
                }
                return $this->transactionManager->trxLevel();
        }

        public function trxTimestamp() {
                return $this->transactionManager->trxTimestamp();
        }

        public function trxStatus() {
                return $this->transactionManager->trxStatus();
        }

        public function writesPending() {
                return $this->transactionManager->writesPending();
        }

        public function writesOrCallbacksPending() {
                return $this->transactionManager->writesOrCallbacksPending();
        }

        public function pendingWriteQueryDuration( $type = self::ESTIMATE_TOTAL ) {
                return $this->transactionManager->pendingWriteQueryDuration( $type );
        }

        public function pendingWriteCallers() {
                if ( !$this->transactionManager ) {
                        return [];
                }
                return $this->transactionManager->pendingWriteCallers();
        }

        public function pendingWriteAndCallbackCallers() {
                if ( !$this->transactionManager ) {
                        return [];
                }
                return $this->transactionManager->pendingWriteAndCallbackCallers();
        }

        public function runOnTransactionPreCommitCallbacks() {
                return $this->transactionManager->runOnTransactionPreCommitCallbacks( $this );
        }

        public function explicitTrxActive() {
                return $this->transactionManager->explicitTrxActive();
        }

        /* End of methods delegated to TransactionManager. */

        /* Start of methods delegated to SQLPlatform. Avoid using them outside of rdbms library */

        public function implicitOrderby() {
                return $this->platform->implicitOrderby();
        }

        public function selectSQLText(
                $tables, $vars, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        ) {
                return $this->platform->selectSQLText( $tables, $vars, $conds, $fname, $options, $join_conds );
        }

        public function buildComparison( string $op, array $conds ): string {
                return $this->platform->buildComparison( $op, $conds );
        }

        public function makeList( array $a, $mode = self::LIST_COMMA ) {
                return $this->platform->makeList( $a, $mode );
        }

        public function makeWhereFrom2d( $data, $baseKey, $subKey ) {
                return $this->platform->makeWhereFrom2d( $data, $baseKey, $subKey );
        }

        public function factorConds( $condsArray ) {
                return $this->platform->factorConds( $condsArray );
        }

        public function bitNot( $field ) {
                return $this->platform->bitNot( $field );
        }

        public function bitAnd( $fieldLeft, $fieldRight ) {
                return $this->platform->bitAnd( $fieldLeft, $fieldRight );
        }

        public function bitOr( $fieldLeft, $fieldRight ) {
                return $this->platform->bitOr( $fieldLeft, $fieldRight );
        }

        public function buildConcat( $stringList ) {
                return $this->platform->buildConcat( $stringList );
        }

        public function buildGreatest( $fields, $values ) {
                return $this->platform->buildGreatest( $fields, $values );
        }

        public function buildLeast( $fields, $values ) {
                return $this->platform->buildLeast( $fields, $values );
        }

        public function buildSubstring( $input, $startPosition, $length = null ) {
                return $this->platform->buildSubstring( $input, $startPosition, $length );
        }

        public function buildStringCast( $field ) {
                return $this->platform->buildStringCast( $field );
        }

        public function buildIntegerCast( $field ) {
                return $this->platform->buildIntegerCast( $field );
        }

        public function tableName( string $name, $format = 'quoted' ) {
                return $this->platform->tableName( $name, $format );
        }

        public function tableNamesN( ...$tables ) {
                return $this->platform->tableNamesN( ...$tables );
        }

        public function addIdentifierQuotes( $s ) {
                return $this->platform->addIdentifierQuotes( $s );
        }

        public function isQuotedIdentifier( $name ) {
                return $this->platform->isQuotedIdentifier( $name );
        }

        public function buildLike( $param, ...$params ) {
                return $this->platform->buildLike( $param, ...$params );
        }

        public function anyChar() {
                return $this->platform->anyChar();
        }

        public function anyString() {
                return $this->platform->anyString();
        }

        public function limitResult( $sql, $limit, $offset = false ) {
                return $this->platform->limitResult( $sql, $limit, $offset );
        }

        public function unionSupportsOrderAndLimit() {
                return $this->platform->unionSupportsOrderAndLimit();
        }

        public function unionQueries( $sqls, $all, $options = [] ) {
                return $this->platform->unionQueries( $sqls, $all, $options );
        }

        public function conditional( $cond, $caseTrueExpression, $caseFalseExpression ) {
                return $this->platform->conditional( $cond, $caseTrueExpression, $caseFalseExpression );
        }

        public function strreplace( $orig, $old, $new ) {
                return $this->platform->strreplace( $orig, $old, $new );
        }

        public function timestamp( $ts = 0 ) {
                return $this->platform->timestamp( $ts );
        }

        public function timestampOrNull( $ts = null ) {
                return $this->platform->timestampOrNull( $ts );
        }

        public function getInfinity() {
                return $this->platform->getInfinity();
        }

        public function encodeExpiry( $expiry ) {
                return $this->platform->encodeExpiry( $expiry );
        }

        public function decodeExpiry( $expiry, $format = TS_MW ) {
                return $this->platform->decodeExpiry( $expiry, $format );
        }

        public function setTableAliases( array $aliases ) {
                $this->platform->setTableAliases( $aliases );
        }

        public function getTableAliases() {
                return $this->platform->getTableAliases();
        }

        public function setIndexAliases( array $aliases ) {
                $this->platform->setIndexAliases( $aliases );
        }

        public function buildGroupConcatField(
                $delim, $tables, $field, $conds = '', $join_conds = []
        ) {
                return $this->platform->buildGroupConcatField( $delim, $tables, $field, $conds, $join_conds );
        }

        public function buildSelectSubquery(
                $tables, $vars, $conds = '', $fname = __METHOD__,
                $options = [], $join_conds = []
        ) {
                return $this->platform->buildSelectSubquery( $tables, $vars, $conds, $fname, $options, $join_conds );
        }

        public function buildExcludedValue( $column ) {
                return $this->platform->buildExcludedValue( $column );
        }

        public function setSchemaVars( $vars ) {
                $this->platform->setSchemaVars( $vars );
        }

        /* End of methods delegated to SQLPlatform. */

        /* Start of methods delegated to ReplicationReporter. */
        public function primaryPosWait( DBPrimaryPos $pos, $timeout ) {
                return $this->replicationReporter->primaryPosWait( $this, $pos, $timeout );
        }

        public function getPrimaryPos() {
                return $this->replicationReporter->getPrimaryPos( $this );
        }

        public function getLag() {
                return $this->replicationReporter->getLag( $this );
        }

        public function getSessionLagStatus() {
                return $this->replicationReporter->getSessionLagStatus( $this );
        }

        /* End of methods delegated to ReplicationReporter. */
}