SessionManager: Change behavior of getSessionById()

[mediawiki.git] / includes / db / DatabaseMysqlBase.php

<?php
/**
 * This is the MySQL database abstraction layer.
 *
 * 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
 * @ingroup Database
 */

/**
 * Database abstraction object for MySQL.
 * Defines methods independent on used MySQL extension.
 *
 * @ingroup Database
 * @since 1.22
 * @see Database
 */
abstract class DatabaseMysqlBase extends Database {
        /** @var MysqlMasterPos */
        protected $lastKnownSlavePos;
        /** @var string Method to detect slave lag */
        protected $lagDetectionMethod;

        /** @var string|null */
        private $serverVersion = null;

        /**
         * Additional $params include:
         *   - lagDetectionMethod : set to one of (Seconds_Behind_Master,pt-heartbeat).
         *                          pt-heartbeat assumes the table is at heartbeat.heartbeat
         *                          and uses UTC timestamps in the heartbeat.ts column.
         *                          (https://www.percona.com/doc/percona-toolkit/2.2/pt-heartbeat.html)
         * @param array $params
         */
        function __construct( array $params ) {
                parent::__construct( $params );

                $this->lagDetectionMethod = isset( $params['lagDetectionMethod'] )
                        ? $params['lagDetectionMethod']
                        : 'Seconds_Behind_Master';
        }

        /**
         * @return string
         */
        function getType() {
                return 'mysql';
        }

        /**
         * @param string $server
         * @param string $user
         * @param string $password
         * @param string $dbName
         * @throws Exception|DBConnectionError
         * @return bool
         */
        function open( $server, $user, $password, $dbName ) {
                global $wgAllDBsAreLocalhost, $wgSQLMode;

                # Close/unset connection handle
                $this->close();

                # Debugging hack -- fake cluster
                $realServer = $wgAllDBsAreLocalhost ? 'localhost' : $server;
                $this->mServer = $server;
                $this->mUser = $user;
                $this->mPassword = $password;
                $this->mDBname = $dbName;

                $this->installErrorHandler();
                try {
                        $this->mConn = $this->mysqlConnect( $realServer );
                } catch ( Exception $ex ) {
                        $this->restoreErrorHandler();
                        throw $ex;
                }
                $error = $this->restoreErrorHandler();

                # Always log connection errors
                if ( !$this->mConn ) {
                        if ( !$error ) {
                                $error = $this->lastError();
                        }
                        wfLogDBError(
                                "Error connecting to {db_server}: {error}",
                                $this->getLogContext( array(
                                        'method' => __METHOD__,
                                        'error' => $error,
                                ) )
                        );
                        wfDebug( "DB connection error\n" .
                                "Server: $server, User: $user, Password: " .
                                substr( $password, 0, 3 ) . "..., error: " . $error . "\n" );

                        $this->reportConnectionError( $error );
                }

                if ( $dbName != '' ) {
                        MediaWiki\suppressWarnings();
                        $success = $this->selectDB( $dbName );
                        MediaWiki\restoreWarnings();
                        if ( !$success ) {
                                wfLogDBError(
                                        "Error selecting database {db_name} on server {db_server}",
                                        $this->getLogContext( array(
                                                'method' => __METHOD__,
                                        ) )
                                );
                                wfDebug( "Error selecting database $dbName on server {$this->mServer} " .
                                        "from client host " . wfHostname() . "\n" );

                                $this->reportConnectionError( "Error selecting database $dbName" );
                        }
                }

                // Tell the server what we're communicating with
                if ( !$this->connectInitCharset() ) {
                        $this->reportConnectionError( "Error setting character set" );
                }

                // Abstract over any insane MySQL defaults
                $set = array( 'group_concat_max_len = 262144' );
                // Set SQL mode, default is turning them all off, can be overridden or skipped with null
                if ( is_string( $wgSQLMode ) ) {
                        $set[] = 'sql_mode = ' . $this->addQuotes( $wgSQLMode );
                }
                // Set any custom settings defined by site config
                // (e.g. https://dev.mysql.com/doc/refman/4.1/en/innodb-parameters.html)
                foreach ( $this->mSessionVars as $var => $val ) {
                        // Escape strings but not numbers to avoid MySQL complaining
                        if ( !is_int( $val ) && !is_float( $val ) ) {
                                $val = $this->addQuotes( $val );
                        }
                        $set[] = $this->addIdentifierQuotes( $var ) . ' = ' . $val;
                }

                if ( $set ) {
                        // Use doQuery() to avoid opening implicit transactions (DBO_TRX)
                        $success = $this->doQuery( 'SET ' . implode( ', ', $set ) );
                        if ( !$success ) {
                                wfLogDBError(
                                        'Error setting MySQL variables on server {db_server} (check $wgSQLMode)',
                                        $this->getLogContext( array(
                                                'method' => __METHOD__,
                                        ) )
                                );
                                $this->reportConnectionError(
                                        'Error setting MySQL variables on server {db_server} (check $wgSQLMode)' );
                        }
                }

                $this->mOpened = true;

                return true;
        }

        /**
         * Set the character set information right after connection
         * @return bool
         */
        protected function connectInitCharset() {
                global $wgDBmysql5;

                if ( $wgDBmysql5 ) {
                        // Tell the server we're communicating with it in UTF-8.
                        // This may engage various charset conversions.
                        return $this->mysqlSetCharset( 'utf8' );
                } else {
                        return $this->mysqlSetCharset( 'binary' );
                }
        }

        /**
         * Open a connection to a MySQL server
         *
         * @param string $realServer
         * @return mixed Raw connection
         * @throws DBConnectionError
         */
        abstract protected function mysqlConnect( $realServer );

        /**
         * Set the character set of the MySQL link
         *
         * @param string $charset
         * @return bool
         */
        abstract protected function mysqlSetCharset( $charset );

        /**
         * @param ResultWrapper|resource $res
         * @throws DBUnexpectedError
         */
        function freeResult( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                MediaWiki\suppressWarnings();
                $ok = $this->mysqlFreeResult( $res );
                MediaWiki\restoreWarnings();
                if ( !$ok ) {
                        throw new DBUnexpectedError( $this, "Unable to free MySQL result" );
                }
        }

        /**
         * Free result memory
         *
         * @param resource $res Raw result
         * @return bool
         */
        abstract protected function mysqlFreeResult( $res );

        /**
         * @param ResultWrapper|resource $res
         * @return stdClass|bool
         * @throws DBUnexpectedError
         */
        function fetchObject( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                MediaWiki\suppressWarnings();
                $row = $this->mysqlFetchObject( $res );
                MediaWiki\restoreWarnings();

                $errno = $this->lastErrno();
                // Unfortunately, mysql_fetch_object does not reset the last errno.
                // Only check for CR_SERVER_LOST and CR_UNKNOWN_ERROR, as
                // these are the only errors mysql_fetch_object can cause.
                // See http://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html.
                if ( $errno == 2000 || $errno == 2013 ) {
                        throw new DBUnexpectedError(
                                $this,
                                'Error in fetchObject(): ' . htmlspecialchars( $this->lastError() )
                        );
                }

                return $row;
        }

        /**
         * Fetch a result row as an object
         *
         * @param resource $res Raw result
         * @return stdClass
         */
        abstract protected function mysqlFetchObject( $res );

        /**
         * @param ResultWrapper|resource $res
         * @return array|bool
         * @throws DBUnexpectedError
         */
        function fetchRow( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                MediaWiki\suppressWarnings();
                $row = $this->mysqlFetchArray( $res );
                MediaWiki\restoreWarnings();

                $errno = $this->lastErrno();
                // Unfortunately, mysql_fetch_array does not reset the last errno.
                // Only check for CR_SERVER_LOST and CR_UNKNOWN_ERROR, as
                // these are the only errors mysql_fetch_array can cause.
                // See http://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html.
                if ( $errno == 2000 || $errno == 2013 ) {
                        throw new DBUnexpectedError(
                                $this,
                                'Error in fetchRow(): ' . htmlspecialchars( $this->lastError() )
                        );
                }

                return $row;
        }

        /**
         * Fetch a result row as an associative and numeric array
         *
         * @param resource $res Raw result
         * @return array
         */
        abstract protected function mysqlFetchArray( $res );

        /**
         * @throws DBUnexpectedError
         * @param ResultWrapper|resource $res
         * @return int
         */
        function numRows( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }
                MediaWiki\suppressWarnings();
                $n = $this->mysqlNumRows( $res );
                MediaWiki\restoreWarnings();

                // Unfortunately, mysql_num_rows does not reset the last errno.
                // We are not checking for any errors here, since
                // these are no errors mysql_num_rows can cause.
                // See http://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html.
                // See https://phabricator.wikimedia.org/T44430
                return $n;
        }

        /**
         * Get number of rows in result
         *
         * @param resource $res Raw result
         * @return int
         */
        abstract protected function mysqlNumRows( $res );

        /**
         * @param ResultWrapper|resource $res
         * @return int
         */
        function numFields( $res ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return $this->mysqlNumFields( $res );
        }

        /**
         * Get number of fields in result
         *
         * @param resource $res Raw result
         * @return int
         */
        abstract protected function mysqlNumFields( $res );

        /**
         * @param ResultWrapper|resource $res
         * @param int $n
         * @return string
         */
        function fieldName( $res, $n ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return $this->mysqlFieldName( $res, $n );
        }

        /**
         * Get the name of the specified field in a result
         *
         * @param ResultWrapper|resource $res
         * @param int $n
         * @return string
         */
        abstract protected function mysqlFieldName( $res, $n );

        /**
         * mysql_field_type() wrapper
         * @param ResultWrapper|resource $res
         * @param int $n
         * @return string
         */
        public function fieldType( $res, $n ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return $this->mysqlFieldType( $res, $n );
        }

        /**
         * Get the type of the specified field in a result
         *
         * @param ResultWrapper|resource $res
         * @param int $n
         * @return string
         */
        abstract protected function mysqlFieldType( $res, $n );

        /**
         * @param ResultWrapper|resource $res
         * @param int $row
         * @return bool
         */
        function dataSeek( $res, $row ) {
                if ( $res instanceof ResultWrapper ) {
                        $res = $res->result;
                }

                return $this->mysqlDataSeek( $res, $row );
        }

        /**
         * Move internal result pointer
         *
         * @param ResultWrapper|resource $res
         * @param int $row
         * @return bool
         */
        abstract protected function mysqlDataSeek( $res, $row );

        /**
         * @return string
         */
        function lastError() {
                if ( $this->mConn ) {
                        # Even if it's non-zero, it can still be invalid
                        MediaWiki\suppressWarnings();
                        $error = $this->mysqlError( $this->mConn );
                        if ( !$error ) {
                                $error = $this->mysqlError();
                        }
                        MediaWiki\restoreWarnings();
                } else {
                        $error = $this->mysqlError();
                }
                if ( $error ) {
                        $error .= ' (' . $this->mServer . ')';
                }

                return $error;
        }

        /**
         * Returns the text of the error message from previous MySQL operation
         *
         * @param resource $conn Raw connection
         * @return string
         */
        abstract protected function mysqlError( $conn = null );

        /**
         * @param string $table
         * @param array $uniqueIndexes
         * @param array $rows
         * @param string $fname
         * @return ResultWrapper
         */
        function replace( $table, $uniqueIndexes, $rows, $fname = __METHOD__ ) {
                return $this->nativeReplace( $table, $rows, $fname );
        }

        /**
         * Estimate rows in dataset
         * Returns estimated count, based on EXPLAIN output
         * Takes same arguments as Database::select()
         *
         * @param string|array $table
         * @param string|array $vars
         * @param string|array $conds
         * @param string $fname
         * @param string|array $options
         * @return bool|int
         */
        public function estimateRowCount( $table, $vars = '*', $conds = '',
                $fname = __METHOD__, $options = array()
        ) {
                $options['EXPLAIN'] = true;
                $res = $this->select( $table, $vars, $conds, $fname, $options );
                if ( $res === false ) {
                        return false;
                }
                if ( !$this->numRows( $res ) ) {
                        return 0;
                }

                $rows = 1;
                foreach ( $res as $plan ) {
                        $rows *= $plan->rows > 0 ? $plan->rows : 1; // avoid resetting to zero
                }

                return (int)$rows;
        }

        /**
         * @param string $table
         * @param string $field
         * @return bool|MySQLField
         */
        function fieldInfo( $table, $field ) {
                $table = $this->tableName( $table );
                $res = $this->query( "SELECT * FROM $table LIMIT 1", __METHOD__, true );
                if ( !$res ) {
                        return false;
                }
                $n = $this->mysqlNumFields( $res->result );
                for ( $i = 0; $i < $n; $i++ ) {
                        $meta = $this->mysqlFetchField( $res->result, $i );
                        if ( $field == $meta->name ) {
                                return new MySQLField( $meta );
                        }
                }

                return false;
        }

        /**
         * Get column information from a result
         *
         * @param resource $res Raw result
         * @param int $n
         * @return stdClass
         */
        abstract protected function mysqlFetchField( $res, $n );

        /**
         * Get information about an index into an object
         * Returns false if the index does not exist
         *
         * @param string $table
         * @param string $index
         * @param string $fname
         * @return bool|array|null False or null on failure
         */
        function indexInfo( $table, $index, $fname = __METHOD__ ) {
                # SHOW INDEX works in MySQL 3.23.58, but SHOW INDEXES does not.
                # SHOW INDEX should work for 3.x and up:
                # http://dev.mysql.com/doc/mysql/en/SHOW_INDEX.html
                $table = $this->tableName( $table );
                $index = $this->indexName( $index );

                $sql = 'SHOW INDEX FROM ' . $table;
                $res = $this->query( $sql, $fname );

                if ( !$res ) {
                        return null;
                }

                $result = array();

                foreach ( $res as $row ) {
                        if ( $row->Key_name == $index ) {
                                $result[] = $row;
                        }
                }

                return empty( $result ) ? false : $result;
        }

        /**
         * @param string $s
         * @return string
         */
        function strencode( $s ) {
                $sQuoted = $this->mysqlRealEscapeString( $s );

                if ( $sQuoted === false ) {
                        $this->ping();
                        $sQuoted = $this->mysqlRealEscapeString( $s );
                }

                return $sQuoted;
        }

        /**
         * @param string $s
         * @return mixed
         */
        abstract protected function mysqlRealEscapeString( $s );

        /**
         * MySQL uses `backticks` for identifier quoting instead of the sql standard "double quotes".
         *
         * @param string $s
         * @return string
         */
        public function addIdentifierQuotes( $s ) {
                // Characters in the range \u0001-\uFFFF are valid in a quoted identifier
                // Remove NUL bytes and escape backticks by doubling
                return '`' . str_replace( array( "\0", '`' ), array( '', '``' ), $s ) . '`';
        }

        /**
         * @param string $name
         * @return bool
         */
        public function isQuotedIdentifier( $name ) {
                return strlen( $name ) && $name[0] == '`' && substr( $name, -1, 1 ) == '`';
        }

        /**
         * @return bool
         */
        function ping() {
                $ping = $this->mysqlPing();
                if ( $ping ) {
                        // Connection was good or lost but reconnected...
                        // @note: mysqlnd (php 5.6+) does not support this (PHP bug 52561)
                        return true;
                }

                // Try a full disconnect/reconnect cycle if ping() failed
                $this->closeConnection();
                $this->mOpened = false;
                $this->mConn = false;
                $this->open( $this->mServer, $this->mUser, $this->mPassword, $this->mDBname );

                return true;
        }

        /**
         * Ping a server connection or reconnect if there is no connection
         *
         * @return bool
         */
        abstract protected function mysqlPing();

        function getLag() {
                if ( $this->getLagDetectionMethod() === 'pt-heartbeat' ) {
                        return $this->getLagFromPtHeartbeat();
                } else {
                        return $this->getLagFromSlaveStatus();
                }
        }

        /**
         * @return string
         */
        protected function getLagDetectionMethod() {
                return $this->lagDetectionMethod;
        }

        /**
         * @return bool|int
         */
        protected function getLagFromSlaveStatus() {
                $res = $this->query( 'SHOW SLAVE STATUS', __METHOD__ );
                $row = $res ? $res->fetchObject() : false;
                if ( $row && strval( $row->Seconds_Behind_Master ) !== '' ) {
                        return intval( $row->Seconds_Behind_Master );
                }

                return false;
        }

        /**
         * @return bool|float
         */
        protected function getLagFromPtHeartbeat() {
                $masterInfo = $this->getMasterServerInfo();
                if ( !$masterInfo ) {
                        wfLogDBError(
                                "Unable to query master of {db_server} for server ID",
                                $this->getLogContext( array(
                                        'method' => __METHOD__
                                ) )
                        );

                        return false; // could not get master server ID
                }

                list( $time, $nowUnix ) = $this->getHeartbeatData( $masterInfo['serverId'] );
                if ( $time !== null ) {
                        // @time is in ISO format like "2015-09-25T16:48:10.000510"
                        $dateTime = new DateTime( $time, new DateTimeZone( 'UTC' ) );
                        $timeUnix = (int)$dateTime->format( 'U' ) + $dateTime->format( 'u' ) / 1e6;

                        return max( $nowUnix - $timeUnix, 0.0 );
                }

                wfLogDBError(
                        "Unable to find pt-heartbeat row for {db_server}",
                        $this->getLogContext( array(
                                'method' => __METHOD__
                        ) )
                );

                return false;
        }

        protected function getMasterServerInfo() {
                $cache = $this->srvCache;
                $key = $cache->makeGlobalKey(
                        'mysql',
                        'master-info',
                        // Using one key for all cluster slaves is preferable
                        $this->getLBInfo( 'clusterMasterHost' ) ?: $this->getServer()
                );

                $that = $this;
                return $cache->getWithSetCallback(
                        $key,
                        $cache::TTL_INDEFINITE,
                        function () use ( $that, $cache, $key ) {
                                // Get and leave a lock key in place for a short period
                                if ( !$cache->lock( $key, 0, 10 ) ) {
                                        return false; // avoid master connection spike slams
                                }

                                $conn = $that->getLazyMasterHandle();
                                if ( !$conn ) {
                                        return false; // something is misconfigured
                                }

                                // Connect to and query the master; catch errors to avoid outages
                                try {
                                        $res = $conn->query( 'SELECT @@server_id AS id', __METHOD__ );
                                        $row = $res ? $res->fetchObject() : false;
                                        $id = $row ? (int)$row->id : 0;
                                } catch ( DBError $e ) {
                                        $id = 0;
                                }

                                // Cache the ID if it was retrieved
                                return $id ? array( 'serverId' => $id, 'asOf' => time() ) : false;
                        }
                );
        }

        /**
         * @param string $masterId Server ID
         * @return array (heartbeat `ts` column value or null, UNIX timestamp)
         * @see https://www.percona.com/doc/percona-toolkit/2.1/pt-heartbeat.html
         */
        protected function getHeartbeatData( $masterId ) {
                // Get the status row for this master; use the oldest for sanity in case the master
                // has entries listed under different server IDs (which should really not happen).
                // Note: this would use "MAX(TIMESTAMPDIFF(MICROSECOND,ts,UTC_TIMESTAMP(6)))" but the
                // percision field is not supported in MySQL <= 5.5.
                $res = $this->query(
                        "SELECT ts FROM heartbeat.heartbeat WHERE server_id=" . intval( $masterId )
                );
                $row = $res ? $res->fetchObject() : false;

                return array( $row ? $row->ts : null, microtime( true ) );
        }

        public function getApproximateLagStatus() {
                if ( $this->getLagDetectionMethod() === 'pt-heartbeat' ) {
                        // Disable caching since this is fast enough and we don't wan't
                        // to be *too* pessimistic by having both the cache TTL and the
                        // pt-heartbeat interval count as lag in getSessionLagStatus()
                        return parent::getApproximateLagStatus();
                }

                $key = $this->srvCache->makeGlobalKey( 'mysql-lag', $this->getServer() );
                $approxLag = $this->srvCache->get( $key );
                if ( !$approxLag ) {
                        $approxLag = parent::getApproximateLagStatus();
                        $this->srvCache->set( $key, $approxLag, 1 );
                }

                return $approxLag;
        }

        /**
         * Wait for the slave to catch up to a given master position.
         * @todo Return values for this and base class are rubbish
         *
         * @param DBMasterPos|MySQLMasterPos $pos
         * @param int $timeout The maximum number of seconds to wait for synchronisation
         * @return int Zero if the slave was past that position already,
         *   greater than zero if we waited for some period of time, less than
         *   zero if we timed out.
         */
        function masterPosWait( DBMasterPos $pos, $timeout ) {
                if ( $this->lastKnownSlavePos && $this->lastKnownSlavePos->hasReached( $pos ) ) {
                        return '0'; // http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html
                }

                # Commit any open transactions
                $this->commit( __METHOD__, 'flush' );

                # Call doQuery() directly, to avoid opening a transaction if DBO_TRX is set
                $encFile = $this->addQuotes( $pos->file );
                $encPos = intval( $pos->pos );
                $sql = "SELECT MASTER_POS_WAIT($encFile, $encPos, $timeout)";
                $res = $this->doQuery( $sql );

                $status = false;
                if ( $res ) {
                        $row = $this->fetchRow( $res );
                        if ( $row ) {
                                $status = $row[0]; // can be NULL, -1, or 0+ per the MySQL manual
                                if ( ctype_digit( $status ) ) { // success
                                        $this->lastKnownSlavePos = $pos;
                                }
                        }
                }

                return $status;
        }

        /**
         * Get the position of the master from SHOW SLAVE STATUS
         *
         * @return MySQLMasterPos|bool
         */
        function getSlavePos() {
                $res = $this->query( 'SHOW SLAVE STATUS', 'DatabaseBase::getSlavePos' );
                $row = $this->fetchObject( $res );

                if ( $row ) {
                        $pos = isset( $row->Exec_master_log_pos )
                                ? $row->Exec_master_log_pos
                                : $row->Exec_Master_Log_Pos;

                        return new MySQLMasterPos( $row->Relay_Master_Log_File, $pos );
                } else {
                        return false;
                }
        }

        /**
         * Get the position of the master from SHOW MASTER STATUS
         *
         * @return MySQLMasterPos|bool
         */
        function getMasterPos() {
                $res = $this->query( 'SHOW MASTER STATUS', 'DatabaseBase::getMasterPos' );
                $row = $this->fetchObject( $res );

                if ( $row ) {
                        return new MySQLMasterPos( $row->File, $row->Position );
                } else {
                        return false;
                }
        }

        /**
         * @param string $index
         * @return string
         */
        function useIndexClause( $index ) {
                return "FORCE INDEX (" . $this->indexName( $index ) . ")";
        }

        /**
         * @return string
         */
        function lowPriorityOption() {
                return 'LOW_PRIORITY';
        }

        /**
         * @return string
         */
        public function getSoftwareLink() {
                // MariaDB includes its name in its version string; this is how MariaDB's version of
                // the mysql command-line client identifies MariaDB servers (see mariadb_connection()
                // in libmysql/libmysql.c).
                $version = $this->getServerVersion();
                if ( strpos( $version, 'MariaDB' ) !== false || strpos( $version, '-maria-' ) !== false ) {
                        return '[{{int:version-db-mariadb-url}} MariaDB]';
                }

                // Percona Server's version suffix is not very distinctive, and @@version_comment
                // doesn't give the necessary info for source builds, so assume the server is MySQL.
                // (Even Percona's version of mysql doesn't try to make the distinction.)
                return '[{{int:version-db-mysql-url}} MySQL]';
        }

        /**
         * @return string
         */
        public function getServerVersion() {
                // Not using mysql_get_server_info() or similar for consistency: in the handshake,
                // MariaDB 10 adds the prefix "5.5.5-", and only some newer client libraries strip
                // it off (see RPL_VERSION_HACK in include/mysql_com.h).
                if ( $this->serverVersion === null ) {
                        $this->serverVersion = $this->selectField( '', 'VERSION()', '', __METHOD__ );
                }
                return $this->serverVersion;
        }

        /**
         * @param array $options
         */
        public function setSessionOptions( array $options ) {
                if ( isset( $options['connTimeout'] ) ) {
                        $timeout = (int)$options['connTimeout'];
                        $this->query( "SET net_read_timeout=$timeout" );
                        $this->query( "SET net_write_timeout=$timeout" );
                }
        }

        /**
         * @param string $sql
         * @param string $newLine
         * @return bool
         */
        public function streamStatementEnd( &$sql, &$newLine ) {
                if ( strtoupper( substr( $newLine, 0, 9 ) ) == 'DELIMITER' ) {
                        preg_match( '/^DELIMITER\s+(\S+)/', $newLine, $m );
                        $this->delimiter = $m[1];
                        $newLine = '';
                }

                return parent::streamStatementEnd( $sql, $newLine );
        }

        /**
         * Check to see if a named lock is available. This is non-blocking.
         *
         * @param string $lockName Name of lock to poll
         * @param string $method Name of method calling us
         * @return bool
         * @since 1.20
         */
        public function lockIsFree( $lockName, $method ) {
                $lockName = $this->addQuotes( $this->makeLockName( $lockName ) );
                $result = $this->query( "SELECT IS_FREE_LOCK($lockName) AS lockstatus", $method );
                $row = $this->fetchObject( $result );

                return ( $row->lockstatus == 1 );
        }

        /**
         * @param string $lockName
         * @param string $method
         * @param int $timeout
         * @return bool
         */
        public function lock( $lockName, $method, $timeout = 5 ) {
                $lockName = $this->addQuotes( $this->makeLockName( $lockName ) );
                $result = $this->query( "SELECT GET_LOCK($lockName, $timeout) AS lockstatus", $method );
                $row = $this->fetchObject( $result );

                if ( $row->lockstatus == 1 ) {
                        return true;
                } else {
                        wfDebug( __METHOD__ . " failed to acquire lock\n" );

                        return false;
                }
        }

        /**
         * FROM MYSQL DOCS:
         * http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_release-lock
         * @param string $lockName
         * @param string $method
         * @return bool
         */
        public function unlock( $lockName, $method ) {
                $lockName = $this->addQuotes( $this->makeLockName( $lockName ) );
                $result = $this->query( "SELECT RELEASE_LOCK($lockName) as lockstatus", $method );
                $row = $this->fetchObject( $result );

                return ( $row->lockstatus == 1 );
        }

        private function makeLockName( $lockName ) {
                // http://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html#function_get-lock
                // Newer version enforce a 64 char length limit.
                return ( strlen( $lockName ) > 64 ) ? sha1( $lockName ) : $lockName;
        }

        public function namedLocksEnqueue() {
                return true;
        }

        /**
         * @param array $read
         * @param array $write
         * @param string $method
         * @param bool $lowPriority
         * @return bool
         */
        public function lockTables( $read, $write, $method, $lowPriority = true ) {
                $items = array();

                foreach ( $write as $table ) {
                        $tbl = $this->tableName( $table ) .
                                ( $lowPriority ? ' LOW_PRIORITY' : '' ) .
                                ' WRITE';
                        $items[] = $tbl;
                }
                foreach ( $read as $table ) {
                        $items[] = $this->tableName( $table ) . ' READ';
                }
                $sql = "LOCK TABLES " . implode( ',', $items );
                $this->query( $sql, $method );

                return true;
        }

        /**
         * @param string $method
         * @return bool
         */
        public function unlockTables( $method ) {
                $this->query( "UNLOCK TABLES", $method );

                return true;
        }

        /**
         * Get search engine class. All subclasses of this
         * need to implement this if they wish to use searching.
         *
         * @return string
         */
        public function getSearchEngine() {
                return 'SearchMySQL';
        }

        /**
         * @param bool $value
         */
        public function setBigSelects( $value = true ) {
                if ( $value === 'default' ) {
                        if ( $this->mDefaultBigSelects === null ) {
                                # Function hasn't been called before so it must already be set to the default
                                return;
                        } else {
                                $value = $this->mDefaultBigSelects;
                        }
                } elseif ( $this->mDefaultBigSelects === null ) {
                        $this->mDefaultBigSelects =
                                (bool)$this->selectField( false, '@@sql_big_selects', '', __METHOD__ );
                }
                $encValue = $value ? '1' : '0';
                $this->query( "SET sql_big_selects=$encValue", __METHOD__ );
        }

        /**
         * DELETE where the condition is a join. MySql uses multi-table deletes.
         * @param string $delTable
         * @param string $joinTable
         * @param string $delVar
         * @param string $joinVar
         * @param array|string $conds
         * @param bool|string $fname
         * @throws DBUnexpectedError
         * @return bool|ResultWrapper
         */
        function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds, $fname = __METHOD__ ) {
                if ( !$conds ) {
                        throw new DBUnexpectedError( $this, 'DatabaseBase::deleteJoin() called with empty $conds' );
                }

                $delTable = $this->tableName( $delTable );
                $joinTable = $this->tableName( $joinTable );
                $sql = "DELETE $delTable FROM $delTable, $joinTable WHERE $delVar=$joinVar ";

                if ( $conds != '*' ) {
                        $sql .= ' AND ' . $this->makeList( $conds, LIST_AND );
                }

                return $this->query( $sql, $fname );
        }

        /**
         * @param string $table
         * @param array $rows
         * @param array $uniqueIndexes
         * @param array $set
         * @param string $fname
         * @return bool
         */
        public function upsert( $table, array $rows, array $uniqueIndexes,
                array $set, $fname = __METHOD__
        ) {
                if ( !count( $rows ) ) {
                        return true; // nothing to do
                }

                if ( !is_array( reset( $rows ) ) ) {
                        $rows = array( $rows );
                }

                $table = $this->tableName( $table );
                $columns = array_keys( $rows[0] );

                $sql = "INSERT INTO $table (" . implode( ',', $columns ) . ') VALUES ';
                $rowTuples = array();
                foreach ( $rows as $row ) {
                        $rowTuples[] = '(' . $this->makeList( $row ) . ')';
                }
                $sql .= implode( ',', $rowTuples );
                $sql .= " ON DUPLICATE KEY UPDATE " . $this->makeList( $set, LIST_SET );

                return (bool)$this->query( $sql, $fname );
        }

        /**
         * Determines how long the server has been up
         *
         * @return int
         */
        function getServerUptime() {
                $vars = $this->getMysqlStatus( 'Uptime' );

                return (int)$vars['Uptime'];
        }

        /**
         * Determines if the last failure was due to a deadlock
         *
         * @return bool
         */
        function wasDeadlock() {
                return $this->lastErrno() == 1213;
        }

        /**
         * Determines if the last failure was due to a lock timeout
         *
         * @return bool
         */
        function wasLockTimeout() {
                return $this->lastErrno() == 1205;
        }

        /**
         * Determines if the last query error was something that should be dealt
         * with by pinging the connection and reissuing the query
         *
         * @return bool
         */
        function wasErrorReissuable() {
                return $this->lastErrno() == 2013 || $this->lastErrno() == 2006;
        }

        /**
         * Determines if the last failure was due to the database being read-only.
         *
         * @return bool
         */
        function wasReadOnlyError() {
                return $this->lastErrno() == 1223 ||
                        ( $this->lastErrno() == 1290 && strpos( $this->lastError(), '--read-only' ) !== false );
        }

        function wasConnectionError( $errno ) {
                return $errno == 2013 || $errno == 2006;
        }

        /**
         * Get the underlying binding handle, mConn
         *
         * Makes sure that mConn 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 resource|object
         * @throws DBUnexpectedError
         * @since 1.26
         */
        protected function getBindingHandle() {
                if ( !$this->mConn ) {
                        throw new DBUnexpectedError(
                                $this,
                                'DB connection was already closed or the connection dropped.'
                        );
                }

                return $this->mConn;
        }

        /**
         * @param string $oldName
         * @param string $newName
         * @param bool $temporary
         * @param string $fname
         * @return bool
         */
        function duplicateTableStructure( $oldName, $newName, $temporary = false, $fname = __METHOD__ ) {
                $tmp = $temporary ? 'TEMPORARY ' : '';
                $newName = $this->addIdentifierQuotes( $newName );
                $oldName = $this->addIdentifierQuotes( $oldName );
                $query = "CREATE $tmp TABLE $newName (LIKE $oldName)";

                return $this->query( $query, $fname );
        }

        /**
         * List all tables on the database
         *
         * @param string $prefix Only show tables with this prefix, e.g. mw_
         * @param string $fname Calling function name
         * @return array
         */
        function listTables( $prefix = null, $fname = __METHOD__ ) {
                $result = $this->query( "SHOW TABLES", $fname );

                $endArray = array();

                foreach ( $result as $table ) {
                        $vars = get_object_vars( $table );
                        $table = array_pop( $vars );

                        if ( !$prefix || strpos( $table, $prefix ) === 0 ) {
                                $endArray[] = $table;
                        }
                }

                return $endArray;
        }

        /**
         * @param string $tableName
         * @param string $fName
         * @return bool|ResultWrapper
         */
        public function dropTable( $tableName, $fName = __METHOD__ ) {
                if ( !$this->tableExists( $tableName, $fName ) ) {
                        return false;
                }

                return $this->query( "DROP TABLE IF EXISTS " . $this->tableName( $tableName ), $fName );
        }

        /**
         * @return array
         */
        protected function getDefaultSchemaVars() {
                $vars = parent::getDefaultSchemaVars();
                $vars['wgDBTableOptions'] = str_replace( 'TYPE', 'ENGINE', $GLOBALS['wgDBTableOptions'] );
                $vars['wgDBTableOptions'] = str_replace(
                        'CHARSET=mysql4',
                        'CHARSET=binary',
                        $vars['wgDBTableOptions']
                );

                return $vars;
        }

        /**
         * Get status information from SHOW STATUS in an associative array
         *
         * @param string $which
         * @return array
         */
        function getMysqlStatus( $which = "%" ) {
                $res = $this->query( "SHOW STATUS LIKE '{$which}'" );
                $status = array();

                foreach ( $res as $row ) {
                        $status[$row->Variable_name] = $row->Value;
                }

                return $status;
        }

        /**
         * Lists VIEWs in the database
         *
         * @param string $prefix Only show VIEWs with this prefix, eg.
         * unit_test_, or $wgDBprefix. Default: null, would return all views.
         * @param string $fname Name of calling function
         * @return array
         * @since 1.22
         */
        public function listViews( $prefix = null, $fname = __METHOD__ ) {

                if ( !isset( $this->allViews ) ) {

                        // The name of the column containing the name of the VIEW
                        $propertyName = 'Tables_in_' . $this->mDBname;

                        // Query for the VIEWS
                        $result = $this->query( 'SHOW FULL TABLES WHERE TABLE_TYPE = "VIEW"' );
                        $this->allViews = array();
                        while ( ( $row = $this->fetchRow( $result ) ) !== false ) {
                                array_push( $this->allViews, $row[$propertyName] );
                        }
                }

                if ( is_null( $prefix ) || $prefix === '' ) {
                        return $this->allViews;
                }

                $filteredViews = array();
                foreach ( $this->allViews as $viewName ) {
                        // Does the name of this VIEW start with the table-prefix?
                        if ( strpos( $viewName, $prefix ) === 0 ) {
                                array_push( $filteredViews, $viewName );
                        }
                }

                return $filteredViews;
        }

        /**
         * Differentiates between a TABLE and a VIEW.
         *
         * @param string $name Name of the TABLE/VIEW to test
         * @param string $prefix
         * @return bool
         * @since 1.22
         */
        public function isView( $name, $prefix = null ) {
                return in_array( $name, $this->listViews( $prefix ) );
        }
}

/**
 * Utility class.
 * @ingroup Database
 */
class MySQLField implements Field {
        private $name, $tablename, $default, $max_length, $nullable,
                $is_pk, $is_unique, $is_multiple, $is_key, $type, $binary,
                $is_numeric, $is_blob, $is_unsigned, $is_zerofill;

        function __construct( $info ) {
                $this->name = $info->name;
                $this->tablename = $info->table;
                $this->default = $info->def;
                $this->max_length = $info->max_length;
                $this->nullable = !$info->not_null;
                $this->is_pk = $info->primary_key;
                $this->is_unique = $info->unique_key;
                $this->is_multiple = $info->multiple_key;
                $this->is_key = ( $this->is_pk || $this->is_unique || $this->is_multiple );
                $this->type = $info->type;
                $this->binary = isset( $info->binary ) ? $info->binary : false;
                $this->is_numeric = isset( $info->numeric ) ? $info->numeric : false;
                $this->is_blob = isset( $info->blob ) ? $info->blob : false;
                $this->is_unsigned = isset( $info->unsigned ) ? $info->unsigned : false;
                $this->is_zerofill = isset( $info->zerofill ) ? $info->zerofill : false;
        }

        /**
         * @return string
         */
        function name() {
                return $this->name;
        }

        /**
         * @return string
         */
        function tableName() {
                return $this->tablename;
        }

        /**
         * @return string
         */
        function type() {
                return $this->type;
        }

        /**
         * @return bool
         */
        function isNullable() {
                return $this->nullable;
        }

        function defaultValue() {
                return $this->default;
        }

        /**
         * @return bool
         */
        function isKey() {
                return $this->is_key;
        }

        /**
         * @return bool
         */
        function isMultipleKey() {
                return $this->is_multiple;
        }

        /**
         * @return bool
         */
        function isBinary() {
                return $this->binary;
        }

        /**
         * @return bool
         */
        function isNumeric() {
                return $this->is_numeric;
        }

        /**
         * @return bool
         */
        function isBlob() {
                return $this->is_blob;
        }

        /**
         * @return bool
         */
        function isUnsigned() {
                return $this->is_unsigned;
        }

        /**
         * @return bool
         */
        function isZerofill() {
                return $this->is_zerofill;
        }
}

class MySQLMasterPos implements DBMasterPos {
        /** @var string */
        public $file;
        /** @var int Position */
        public $pos;
        /** @var float UNIX timestamp */
        public $asOfTime = 0.0;

        function __construct( $file, $pos ) {
                $this->file = $file;
                $this->pos = $pos;
                $this->asOfTime = microtime( true );
        }

        function asOfTime() {
                return $this->asOfTime;
        }

        function hasReached( DBMasterPos $pos ) {
                if ( !( $pos instanceof self ) ) {
                        throw new InvalidArgumentException( "Position not an instance of " . __CLASS__ );
                }

                $thisPos = $this->getCoordinates();
                $thatPos = $pos->getCoordinates();

                return ( $thisPos && $thatPos && $thisPos >= $thatPos );
        }

        function __toString() {
                // e.g db1034-bin.000976/843431247
                return "{$this->file}/{$this->pos}";
        }

        /**
         * @return array|bool (int, int)
         */
        protected function getCoordinates() {
                $m = array();
                if ( preg_match( '!\.(\d+)/(\d+)$!', (string)$this, $m ) ) {
                        return array( (int)$m[1], (int)$m[2] );
                }

                return false;
        }
}