DifferenceEngine cleanup

[mediawiki.git] / includes / installer / DatabaseUpdater.php

<?php
/**
 * DBMS-specific updater helper.
 *
 * 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 Deployment
 */

require_once __DIR__ . '/../../maintenance/Maintenance.php';

/**
 * Class for handling database updates. Roughly based off of updaters.inc, with
 * a few improvements :)
 *
 * @ingroup Deployment
 * @since 1.17
 */
abstract class DatabaseUpdater {

        /**
         * Array of updates to perform on the database
         *
         * @var array
         */
        protected $updates = array();

        /**
         * Array of updates that were skipped
         *
         * @var array
         */
        protected $updatesSkipped = array();

        /**
         * List of extension-provided database updates
         * @var array
         */
        protected $extensionUpdates = array();

        /**
         * Handle to the database subclass
         *
         * @var DatabaseBase
         */
        protected $db;

        protected $shared = false;

        /**
         * Scripts to run after database update
         * Should be a subclass of LoggedUpdateMaintenance
         */
        protected $postDatabaseUpdateMaintenance = array(
                'DeleteDefaultMessages',
                'PopulateRevisionLength',
                'PopulateRevisionSha1',
                'PopulateImageSha1',
                'FixExtLinksProtocolRelative',
                'PopulateFilearchiveSha1',
        );

        /**
         * File handle for SQL output.
         *
         * @var resource
         */
        protected $fileHandle = null;

        /**
         * Flag specifying whether or not to skip schema (e.g. SQL-only) updates.
         *
         * @var bool
         */
        protected $skipSchema = false;

        /**
         * Hold the value of $wgContentHandlerUseDB during the upgrade.
         */
        protected $holdContentHandlerUseDB = true;

        /**
         * Constructor
         *
         * @param DatabaseBase $db To perform updates on
         * @param bool $shared Whether to perform updates on shared tables
         * @param Maintenance $maintenance Maintenance object which created us
         */
        protected function __construct( DatabaseBase &$db, $shared, Maintenance $maintenance = null ) {
                $this->db = $db;
                $this->db->setFlag( DBO_DDLMODE ); // For Oracle's handling of schema files
                $this->shared = $shared;
                if ( $maintenance ) {
                        $this->maintenance = $maintenance;
                        $this->fileHandle = $maintenance->fileHandle;
                } else {
                        $this->maintenance = new FakeMaintenance;
                }
                $this->maintenance->setDB( $db );
                $this->initOldGlobals();
                $this->loadExtensions();
                wfRunHooks( 'LoadExtensionSchemaUpdates', array( $this ) );
        }

        /**
         * Initialize all of the old globals. One day this should all become
         * something much nicer
         */
        private function initOldGlobals() {
                global $wgExtNewTables, $wgExtNewFields, $wgExtPGNewFields,
                        $wgExtPGAlteredFields, $wgExtNewIndexes, $wgExtModifiedFields;

                # For extensions only, should be populated via hooks
                # $wgDBtype should be checked to specifiy the proper file
                $wgExtNewTables = array(); // table, dir
                $wgExtNewFields = array(); // table, column, dir
                $wgExtPGNewFields = array(); // table, column, column attributes; for PostgreSQL
                $wgExtPGAlteredFields = array(); // table, column, new type, conversion method; for PostgreSQL
                $wgExtNewIndexes = array(); // table, index, dir
                $wgExtModifiedFields = array(); // table, index, dir
        }

        /**
         * Loads LocalSettings.php, if needed, and initialises everything needed for
         * LoadExtensionSchemaUpdates hook.
         */
        private function loadExtensions() {
                if ( !defined( 'MEDIAWIKI_INSTALL' ) ) {
                        return; // already loaded
                }
                $vars = Installer::getExistingLocalSettings();
                if ( !$vars ) {
                        return; // no LocalSettings found
                }
                if ( !isset( $vars['wgHooks'] ) || !isset( $vars['wgHooks']['LoadExtensionSchemaUpdates'] ) ) {
                        return;
                }
                global $wgHooks, $wgAutoloadClasses;
                $wgHooks['LoadExtensionSchemaUpdates'] = $vars['wgHooks']['LoadExtensionSchemaUpdates'];
                $wgAutoloadClasses = $wgAutoloadClasses + $vars['wgAutoloadClasses'];
        }

        /**
         * @throws MWException
         * @param DatabaseBase $db
         * @param bool $shared
         * @param null $maintenance
         * @return DatabaseUpdater
         */
        public static function newForDB( &$db, $shared = false, $maintenance = null ) {
                $type = $db->getType();
                if ( in_array( $type, Installer::getDBTypes() ) ) {
                        $class = ucfirst( $type ) . 'Updater';

                        return new $class( $db, $shared, $maintenance );
                } else {
                        throw new MWException( __METHOD__ . ' called for unsupported $wgDBtype' );
                }
        }

        /**
         * Get a database connection to run updates
         *
         * @return DatabaseBase
         */
        public function getDB() {
                return $this->db;
        }

        /**
         * Output some text. If we're running from web, escape the text first.
         *
         * @param string $str Text to output
         */
        public function output( $str ) {
                if ( $this->maintenance->isQuiet() ) {
                        return;
                }
                global $wgCommandLineMode;
                if ( !$wgCommandLineMode ) {
                        $str = htmlspecialchars( $str );
                }
                echo $str;
                flush();
        }

        /**
         * Add a new update coming from an extension. This should be called by
         * extensions while executing the LoadExtensionSchemaUpdates hook.
         *
         * @since 1.17
         *
         * @param array $update The update to run. Format is the following:
         *                first item is the callback function, it also can be a
         *                simple string with the name of a function in this class,
         *                following elements are parameters to the function.
         *                Note that callback functions will receive this object as
         *                first parameter.
         */
        public function addExtensionUpdate( array $update ) {
                $this->extensionUpdates[] = $update;
        }

        /**
         * Convenience wrapper for addExtensionUpdate() when adding a new table (which
         * is the most common usage of updaters in an extension)
         *
         * @since 1.18
         *
         * @param string $tableName Name of table to create
         * @param string $sqlPath Full path to the schema file
         */
        public function addExtensionTable( $tableName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'addTable', $tableName, $sqlPath, true );
        }

        /**
         * @since 1.19
         *
         * @param $tableName string
         * @param $indexName string
         * @param $sqlPath string
         */
        public function addExtensionIndex( $tableName, $indexName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'addIndex', $tableName, $indexName, $sqlPath, true );
        }

        /**
         *
         * @since 1.19
         *
         * @param $tableName string
         * @param $columnName string
         * @param $sqlPath string
         */
        public function addExtensionField( $tableName, $columnName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'addField', $tableName, $columnName, $sqlPath, true );
        }

        /**
         *
         * @since 1.20
         *
         * @param $tableName string
         * @param $columnName string
         * @param $sqlPath string
         */
        public function dropExtensionField( $tableName, $columnName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'dropField', $tableName, $columnName, $sqlPath, true );
        }

        /**
         * Drop an index from an extension table
         *
         * @since 1.21
         *
         * @param string $tableName The table name
         * @param string $indexName The index name
         * @param string $sqlPath The path to the SQL change path
         */
        public function dropExtensionIndex( $tableName, $indexName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'dropIndex', $tableName, $indexName, $sqlPath, true );
        }

        /**
         *
         * @since 1.20
         *
         * @param $tableName string
         * @param $sqlPath string
         */
        public function dropExtensionTable( $tableName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'dropTable', $tableName, $sqlPath, true );
        }

        /**
         * Rename an index on an extension table
         *
         * @since 1.21
         *
         * @param string $tableName The table name
         * @param string $oldIndexName The old index name
         * @param string $newIndexName The new index name
         * @param $skipBothIndexExistWarning Boolean: Whether to warn if both the old
         * and the new indexes exist. [facultative; by default, false]
         * @param string $sqlPath The path to the SQL change path
         */
        public function renameExtensionIndex( $tableName, $oldIndexName, $newIndexName,
                $sqlPath, $skipBothIndexExistWarning = false
        ) {
                $this->extensionUpdates[] = array(
                        'renameIndex',
                        $tableName,
                        $oldIndexName,
                        $newIndexName,
                        $skipBothIndexExistWarning,
                        $sqlPath,
                        true
                );
        }

        /**
         * @since 1.21
         *
         * @param string $tableName The table name
         * @param string $fieldName The field to be modified
         * @param string $sqlPath The path to the SQL change path
         */
        public function modifyExtensionField( $tableName, $fieldName, $sqlPath ) {
                $this->extensionUpdates[] = array( 'modifyField', $tableName, $fieldName, $sqlPath, true );
        }

        /**
         *
         * @since 1.20
         *
         * @param $tableName string
         * @return bool
         */
        public function tableExists( $tableName ) {
                return ( $this->db->tableExists( $tableName, __METHOD__ ) );
        }

        /**
         * Add a maintenance script to be run after the database updates are complete.
         *
         * Script should subclass LoggedUpdateMaintenance
         *
         * @since 1.19
         *
         * @param string $class Name of a Maintenance subclass
         */
        public function addPostDatabaseUpdateMaintenance( $class ) {
                $this->postDatabaseUpdateMaintenance[] = $class;
        }

        /**
         * Get the list of extension-defined updates
         *
         * @return Array
         */
        protected function getExtensionUpdates() {
                return $this->extensionUpdates;
        }

        /**
         * @since 1.17
         *
         * @return array
         */
        public function getPostDatabaseUpdateMaintenance() {
                return $this->postDatabaseUpdateMaintenance;
        }

        /**
         * @since 1.21
         *
         * Writes the schema updates desired to a file for the DB Admin to run.
         */
        private function writeSchemaUpdateFile( $schemaUpdate = array() ) {
                $updates = $this->updatesSkipped;
                $this->updatesSkipped = array();

                foreach ( $updates as $funcList ) {
                        $func = $funcList[0];
                        $arg = $funcList[1];
                        $origParams = $funcList[2];
                        call_user_func_array( $func, $arg );
                        flush();
                        $this->updatesSkipped[] = $origParams;
                }
        }

        /**
         * Do all the updates
         *
         * @param array $what What updates to perform
         */
        public function doUpdates( $what = array( 'core', 'extensions', 'stats' ) ) {
                global $wgVersion;

                $this->db->begin( __METHOD__ );
                $what = array_flip( $what );
                $this->skipSchema = isset( $what['noschema'] ) || $this->fileHandle !== null;
                if ( isset( $what['core'] ) ) {
                        $this->runUpdates( $this->getCoreUpdateList(), false );
                }
                if ( isset( $what['extensions'] ) ) {
                        $this->runUpdates( $this->getOldGlobalUpdates(), false );
                        $this->runUpdates( $this->getExtensionUpdates(), true );
                }

                if ( isset( $what['stats'] ) ) {
                        $this->checkStats();
                }

                $this->setAppliedUpdates( $wgVersion, $this->updates );

                if ( $this->fileHandle ) {
                        $this->skipSchema = false;
                        $this->writeSchemaUpdateFile();
                        $this->setAppliedUpdates( "$wgVersion-schema", $this->updatesSkipped );
                }

                $this->db->commit( __METHOD__ );
        }

        /**
         * Helper function for doUpdates()
         *
         * @param array $updates of updates to run
         * @param bool $passSelf Whether to pass this object we calling external
         *                  functions
         */
        private function runUpdates( array $updates, $passSelf ) {
                $updatesDone = array();
                $updatesSkipped = array();
                foreach ( $updates as $params ) {
                        $origParams = $params;
                        $func = array_shift( $params );
                        if ( !is_array( $func ) && method_exists( $this, $func ) ) {
                                $func = array( $this, $func );
                        } elseif ( $passSelf ) {
                                array_unshift( $params, $this );
                        }
                        $ret = call_user_func_array( $func, $params );
                        flush();
                        if ( $ret !== false ) {
                                $updatesDone[] = $origParams;
                        } else {
                                $updatesSkipped[] = array( $func, $params, $origParams );
                        }
                }
                $this->updatesSkipped = array_merge( $this->updatesSkipped, $updatesSkipped );
                $this->updates = array_merge( $this->updates, $updatesDone );
        }

        /**
         * @param string $version
         * @param array $updates
         */
        protected function setAppliedUpdates( $version, $updates = array() ) {
                $this->db->clearFlag( DBO_DDLMODE );
                if ( !$this->canUseNewUpdatelog() ) {
                        return;
                }
                $key = "updatelist-$version-" . time();
                $this->db->insert( 'updatelog',
                        array( 'ul_key' => $key, 'ul_value' => serialize( $updates ) ),
                        __METHOD__ );
                $this->db->setFlag( DBO_DDLMODE );
        }

        /**
         * Helper function: check if the given key is present in the updatelog table.
         * Obviously, only use this for updates that occur after the updatelog table was
         * created!
         * @param string $key Name of the key to check for
         * @return bool
         */
        public function updateRowExists( $key ) {
                $row = $this->db->selectRow(
                        'updatelog',
                        '1',
                        array( 'ul_key' => $key ),
                        __METHOD__
                );

                return (bool)$row;
        }

        /**
         * Helper function: Add a key to the updatelog table
         * Obviously, only use this for updates that occur after the updatelog table was
         * created!
         * @param string $key Name of key to insert
         * @param string $val [optional] Value to insert along with the key
         */
        public function insertUpdateRow( $key, $val = null ) {
                $this->db->clearFlag( DBO_DDLMODE );
                $values = array( 'ul_key' => $key );
                if ( $val && $this->canUseNewUpdatelog() ) {
                        $values['ul_value'] = $val;
                }
                $this->db->insert( 'updatelog', $values, __METHOD__, 'IGNORE' );
                $this->db->setFlag( DBO_DDLMODE );
        }

        /**
         * Updatelog was changed in 1.17 to have a ul_value column so we can record
         * more information about what kind of updates we've done (that's what this
         * class does). Pre-1.17 wikis won't have this column, and really old wikis
         * might not even have updatelog at all
         *
         * @return boolean
         */
        protected function canUseNewUpdatelog() {
                return $this->db->tableExists( 'updatelog', __METHOD__ ) &&
                        $this->db->fieldExists( 'updatelog', 'ul_value', __METHOD__ );
        }

        /**
         * Returns whether updates should be executed on the database table $name.
         * Updates will be prevented if the table is a shared table and it is not
         * specified to run updates on shared tables.
         *
         * @param string $name Table name
         * @return bool
         */
        protected function doTable( $name ) {
                global $wgSharedDB, $wgSharedTables;

                // Don't bother to check $wgSharedTables if there isn't a shared database
                // or the user actually also wants to do updates on the shared database.
                if ( $wgSharedDB === null || $this->shared ) {
                        return true;
                }

                return !in_array( $name, $wgSharedTables );
        }

        /**
         * Before 1.17, we used to handle updates via stuff like
         * $wgExtNewTables/Fields/Indexes. This is nasty :) We refactored a lot
         * of this in 1.17 but we want to remain back-compatible for a while. So
         * load up these old global-based things into our update list.
         *
         * @return array
         */
        protected function getOldGlobalUpdates() {
                global $wgExtNewFields, $wgExtNewTables, $wgExtModifiedFields,
                        $wgExtNewIndexes;

                $updates = array();

                foreach ( $wgExtNewTables as $tableRecord ) {
                        $updates[] = array(
                                'addTable', $tableRecord[0], $tableRecord[1], true
                        );
                }

                foreach ( $wgExtNewFields as $fieldRecord ) {
                        $updates[] = array(
                                'addField', $fieldRecord[0], $fieldRecord[1],
                                $fieldRecord[2], true
                        );
                }

                foreach ( $wgExtNewIndexes as $fieldRecord ) {
                        $updates[] = array(
                                'addIndex', $fieldRecord[0], $fieldRecord[1],
                                $fieldRecord[2], true
                        );
                }

                foreach ( $wgExtModifiedFields as $fieldRecord ) {
                        $updates[] = array(
                                'modifyField', $fieldRecord[0], $fieldRecord[1],
                                $fieldRecord[2], true
                        );
                }

                return $updates;
        }

        /**
         * Get an array of updates to perform on the database. Should return a
         * multi-dimensional array. The main key is the MediaWiki version (1.12,
         * 1.13...) with the values being arrays of updates, identical to how
         * updaters.inc did it (for now)
         *
         * @return array
         */
        abstract protected function getCoreUpdateList();

        /**
         * Append an SQL fragment to the open file handle.
         *
         * @param string $filename File name to open
         */
        public function copyFile( $filename ) {
                $this->db->sourceFile( $filename, false, false, false,
                        array( $this, 'appendLine' )
                );
        }

        /**
         * Append a line to the open filehandle.  The line is assumed to
         * be a complete SQL statement.
         *
         * This is used as a callback for for sourceLine().
         *
         * @param string $line Text to append to the file
         * @return bool False to skip actually executing the file
         * @throws MWException
         */
        public function appendLine( $line ) {
                $line = rtrim( $line ) . ";\n";
                if ( fwrite( $this->fileHandle, $line ) === false ) {
                        throw new MWException( "trouble writing file" );
                }

                return false;
        }

        /**
         * Applies a SQL patch
         *
         * @param string $path Path to the patch file
         * @param $isFullPath Boolean Whether to treat $path as a relative or not
         * @param string $msg Description of the patch
         * @return bool False if patch is skipped.
         */
        protected function applyPatch( $path, $isFullPath = false, $msg = null ) {
                if ( $msg === null ) {
                        $msg = "Applying $path patch";
                }
                if ( $this->skipSchema ) {
                        $this->output( "...skipping schema change ($msg).\n" );

                        return false;
                }

                $this->output( "$msg ..." );

                if ( !$isFullPath ) {
                        $path = $this->db->patchPath( $path );
                }
                if ( $this->fileHandle !== null ) {
                        $this->copyFile( $path );
                } else {
                        $this->db->sourceFile( $path );
                }
                $this->output( "done.\n" );

                return true;
        }

        /**
         * Add a new table to the database
         *
         * @param string $name Name of the new table
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        protected function addTable( $name, $patch, $fullpath = false ) {
                if ( !$this->doTable( $name ) ) {
                        return true;
                }

                if ( $this->db->tableExists( $name, __METHOD__ ) ) {
                        $this->output( "...$name table already exists.\n" );
                } else {
                        return $this->applyPatch( $patch, $fullpath, "Creating $name table" );
                }

                return true;
        }

        /**
         * Add a new field to an existing table
         *
         * @param string $table Name of the table to modify
         * @param string $field Name of the new field
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        protected function addField( $table, $field, $patch, $fullpath = false ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                if ( !$this->db->tableExists( $table, __METHOD__ ) ) {
                        $this->output( "...$table table does not exist, skipping new field patch.\n" );
                } elseif ( $this->db->fieldExists( $table, $field, __METHOD__ ) ) {
                        $this->output( "...have $field field in $table table.\n" );
                } else {
                        return $this->applyPatch( $patch, $fullpath, "Adding $field field to table $table" );
                }

                return true;
        }

        /**
         * Add a new index to an existing table
         *
         * @param string $table Name of the table to modify
         * @param string $index Name of the new index
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        protected function addIndex( $table, $index, $patch, $fullpath = false ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                if ( !$this->db->tableExists( $table, __METHOD__ ) ) {
                        $this->output( "...skipping: '$table' table doesn't exist yet.\n" );
                } elseif ( $this->db->indexExists( $table, $index, __METHOD__ ) ) {
                        $this->output( "...index $index already set on $table table.\n" );
                } else {
                        return $this->applyPatch( $patch, $fullpath, "Adding index $index to table $table" );
                }

                return true;
        }

        /**
         * Drop a field from an existing table
         *
         * @param string $table Name of the table to modify
         * @param string $field Name of the old field
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        protected function dropField( $table, $field, $patch, $fullpath = false ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                if ( $this->db->fieldExists( $table, $field, __METHOD__ ) ) {
                        return $this->applyPatch( $patch, $fullpath, "Table $table contains $field field. Dropping" );
                } else {
                        $this->output( "...$table table does not contain $field field.\n" );
                }

                return true;
        }

        /**
         * Drop an index from an existing table
         *
         * @param string $table Name of the table to modify
         * @param string $index Name of the index
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        protected function dropIndex( $table, $index, $patch, $fullpath = false ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                if ( $this->db->indexExists( $table, $index, __METHOD__ ) ) {
                        return $this->applyPatch( $patch, $fullpath, "Dropping $index index from table $table" );
                } else {
                        $this->output( "...$index key doesn't exist.\n" );
                }

                return true;
        }

        /**
         * Rename an index from an existing table
         *
         * @param string $table Name of the table to modify
         * @param string $oldIndex Old name of the index
         * @param string $newIndex New name of the index
         * @param $skipBothIndexExistWarning Boolean: Whether to warn if both the
         * old and the new indexes exist.
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        protected function renameIndex( $table, $oldIndex, $newIndex,
                $skipBothIndexExistWarning, $patch, $fullpath = false
        ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                // First requirement: the table must exist
                if ( !$this->db->tableExists( $table, __METHOD__ ) ) {
                        $this->output( "...skipping: '$table' table doesn't exist yet.\n" );

                        return true;
                }

                // Second requirement: the new index must be missing
                if ( $this->db->indexExists( $table, $newIndex, __METHOD__ ) ) {
                        $this->output( "...index $newIndex already set on $table table.\n" );
                        if ( !$skipBothIndexExistWarning &&
                                $this->db->indexExists( $table, $oldIndex, __METHOD__ )
                        ) {
                                $this->output( "...WARNING: $oldIndex still exists, despite it has " .
                                        "been renamed into $newIndex (which also exists).\n" .
                                        "            $oldIndex should be manually removed if not needed anymore.\n" );
                        }

                        return true;
                }

                // Third requirement: the old index must exist
                if ( !$this->db->indexExists( $table, $oldIndex, __METHOD__ ) ) {
                        $this->output( "...skipping: index $oldIndex doesn't exist.\n" );

                        return true;
                }

                // Requirements have been satisfied, patch can be applied
                return $this->applyPatch(
                        $patch,
                        $fullpath,
                        "Renaming index $oldIndex into $newIndex to table $table"
                );
        }

        /**
         * If the specified table exists, drop it, or execute the
         * patch if one is provided.
         *
         * Public @since 1.20
         *
         * @param string $table Table to drop.
         * @param string|bool $patch String of patch file that will drop the table. Default: false.
         * @param bool $fullpath Whether $patch is a full path. Default: false.
         * @return bool False if this was skipped because schema changes are skipped
         */
        public function dropTable( $table, $patch = false, $fullpath = false ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                if ( $this->db->tableExists( $table, __METHOD__ ) ) {
                        $msg = "Dropping table $table";

                        if ( $patch === false ) {
                                $this->output( "$msg ..." );
                                $this->db->dropTable( $table, __METHOD__ );
                                $this->output( "done.\n" );
                        } else {
                                return $this->applyPatch( $patch, $fullpath, $msg );
                        }
                } else {
                        $this->output( "...$table doesn't exist.\n" );
                }

                return true;
        }

        /**
         * Modify an existing field
         *
         * @param string $table Name of the table to which the field belongs
         * @param string $field Name of the field to modify
         * @param string $patch Path to the patch file
         * @param bool $fullpath Whether to treat $patch path as a relative or not
         * @return bool False if this was skipped because schema changes are skipped
         */
        public function modifyField( $table, $field, $patch, $fullpath = false ) {
                if ( !$this->doTable( $table ) ) {
                        return true;
                }

                $updateKey = "$table-$field-$patch";
                if ( !$this->db->tableExists( $table, __METHOD__ ) ) {
                        $this->output( "...$table table does not exist, skipping modify field patch.\n" );
                } elseif ( !$this->db->fieldExists( $table, $field, __METHOD__ ) ) {
                        $this->output( "...$field field does not exist in $table table, " .
                                "skipping modify field patch.\n" );
                } elseif ( $this->updateRowExists( $updateKey ) ) {
                        $this->output( "...$field in table $table already modified by patch $patch.\n" );
                } else {
                        $this->insertUpdateRow( $updateKey );

                        return $this->applyPatch( $patch, $fullpath, "Modifying $field field of table $table" );
                }

                return true;
        }

        /**
         * Purge the objectcache table
         */
        public function purgeCache() {
                global $wgLocalisationCacheConf;
                # We can't guarantee that the user will be able to use TRUNCATE,
                # but we know that DELETE is available to us
                $this->output( "Purging caches..." );
                $this->db->delete( 'objectcache', '*', __METHOD__ );
                if ( $wgLocalisationCacheConf['manualRecache'] ) {
                        $this->rebuildLocalisationCache();
                }
                MessageBlobStore::clear();
                $this->output( "done.\n" );
        }

        /**
         * Check the site_stats table is not properly populated.
         */
        protected function checkStats() {
                $this->output( "...site_stats is populated..." );
                $row = $this->db->selectRow( 'site_stats', '*', array( 'ss_row_id' => 1 ), __METHOD__ );
                if ( $row === false ) {
                        $this->output( "data is missing! rebuilding...\n" );
                } elseif ( isset( $row->site_stats ) && $row->ss_total_pages == -1 ) {
                        $this->output( "missing ss_total_pages, rebuilding...\n" );
                } else {
                        $this->output( "done.\n" );

                        return;
                }
                SiteStatsInit::doAllAndCommit( $this->db );
        }

        # Common updater functions

        /**
         * Sets the number of active users in the site_stats table
         */
        protected function doActiveUsersInit() {
                $activeUsers = $this->db->selectField( 'site_stats', 'ss_active_users', false, __METHOD__ );
                if ( $activeUsers == -1 ) {
                        $activeUsers = $this->db->selectField( 'recentchanges',
                                'COUNT( DISTINCT rc_user_text )',
                                array( 'rc_user != 0', 'rc_bot' => 0, "rc_log_type != 'newusers'" ), __METHOD__
                        );
                        $this->db->update( 'site_stats',
                                array( 'ss_active_users' => intval( $activeUsers ) ),
                                array( 'ss_row_id' => 1 ), __METHOD__, array( 'LIMIT' => 1 )
                        );
                }
                $this->output( "...ss_active_users user count set...\n" );
        }

        /**
         * Populates the log_user_text field in the logging table
         */
        protected function doLogUsertextPopulation() {
                if ( !$this->updateRowExists( 'populate log_usertext' ) ) {
                        $this->output(
                                "Populating log_user_text field, printing progress markers. For large\n" .
                                "databases, you may want to hit Ctrl-C and do this manually with\n" .
                                "maintenance/populateLogUsertext.php.\n"
                        );

                        $task = $this->maintenance->runChild( 'PopulateLogUsertext' );
                        $task->execute();
                        $this->output( "done.\n" );
                }
        }

        /**
         * Migrate log params to new table and index for searching
         */
        protected function doLogSearchPopulation() {
                if ( !$this->updateRowExists( 'populate log_search' ) ) {
                        $this->output(
                                "Populating log_search table, printing progress markers. For large\n" .
                                "databases, you may want to hit Ctrl-C and do this manually with\n" .
                                "maintenance/populateLogSearch.php.\n" );

                        $task = $this->maintenance->runChild( 'PopulateLogSearch' );
                        $task->execute();
                        $this->output( "done.\n" );
                }
        }

        /**
         * Updates the timestamps in the transcache table
         */
        protected function doUpdateTranscacheField() {
                if ( $this->updateRowExists( 'convert transcache field' ) ) {
                        $this->output( "...transcache tc_time already converted.\n" );

                        return true;
                }

                return $this->applyPatch( 'patch-tc-timestamp.sql', false,
                        "Converting tc_time from UNIX epoch to MediaWiki timestamp" );
        }

        /**
         * Update CategoryLinks collation
         */
        protected function doCollationUpdate() {
                global $wgCategoryCollation;
                if ( $this->db->fieldExists( 'categorylinks', 'cl_collation', __METHOD__ ) ) {
                        if ( $this->db->selectField(
                                'categorylinks',
                                'COUNT(*)',
                                'cl_collation != ' . $this->db->addQuotes( $wgCategoryCollation ),
                                __METHOD__
                                ) == 0
                        ) {
                                $this->output( "...collations up-to-date.\n" );

                                return;
                        }

                        $this->output( "Updating category collations..." );
                        $task = $this->maintenance->runChild( 'UpdateCollation' );
                        $task->execute();
                        $this->output( "...done.\n" );
                }
        }

        /**
         * Migrates user options from the user table blob to user_properties
         */
        protected function doMigrateUserOptions() {
                if ( $this->db->tableExists( 'user_properties' ) ) {
                        $cl = $this->maintenance->runChild( 'ConvertUserOptions', 'convertUserOptions.php' );
                        $cl->execute();
                        $this->output( "done.\n" );
                }
        }

        /**
         * Rebuilds the localisation cache
         */
        protected function rebuildLocalisationCache() {
                /**
                 * @var $cl RebuildLocalisationCache
                 */
                $cl = $this->maintenance->runChild( 'RebuildLocalisationCache', 'rebuildLocalisationCache.php' );
                $this->output( "Rebuilding localisation cache...\n" );
                $cl->setForce();
                $cl->execute();
                $this->output( "done.\n" );
        }

        /**
         * Turns off content handler fields during parts of the upgrade
         * where they aren't available.
         */
        protected function disableContentHandlerUseDB() {
                global $wgContentHandlerUseDB;

                if( $wgContentHandlerUseDB ) {
                        $this->output( "Turning off Content Handler DB fields for this part of upgrade.\n" );
                        $this->holdContentHandlerUseDB = $wgContentHandlerUseDB;
                        $wgContentHandlerUseDB = false;
                }
        }

        /**
         * Turns content handler fields back on.
         */
        protected function enableContentHandlerUseDB() {
                global $wgContentHandlerUseDB;

                if( $this->holdContentHandlerUseDB ) {
                        $this->output( "Content Handler DB fields should be usable now.\n" );
                        $wgContentHandlerUseDB = $this->holdContentHandlerUseDB;
                }
        }
}