populateParentId.php

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<?php
require_once( __DIR__ . '/Maintenance.php' );

class PopulateParentId extends LoggedUpdateMaintenance {
        public function __construct() {
                parent::__construct();
                $this->mDescription = "Populates rev_parent_id";
        }

        protected function getUpdateKey() {
                return 'populate rev_parent_id';
        }

        protected function updateSkippedMessage() {
                return 'rev_parent_id column of revision table already populated.';
        }

        protected function doDBUpdates() {
                $db = wfGetDB( DB_MASTER );
                if ( !$db->tableExists( 'revision' ) ) {
                        $this->error( "revision table does not exist" );
                        return false;
                }
                $this->output( "Populating rev_parent_id column\n" );
                $start = $db->selectField( 'revision', 'MIN(rev_id)', false, __FUNCTION__ );
                $end = $db->selectField( 'revision', 'MAX(rev_id)', false, __FUNCTION__ );
                if ( is_null( $start ) || is_null( $end ) ) {
                        $this->output( "...revision table seems to be empty, nothing to do.\n" );
                        return true;
                }
                # Do remaining chunk
                $blockStart = intval( $start );
                $blockEnd = intval( $start ) + $this->mBatchSize - 1;
                $count = 0;
                $changed = 0;
                while ( $blockStart <= $end ) {
                        $this->output( "...doing rev_id from $blockStart to $blockEnd\n" );
                        $cond = "rev_id BETWEEN $blockStart AND $blockEnd";
                        $res = $db->select( 'revision',
                                array( 'rev_id', 'rev_page', 'rev_timestamp', 'rev_parent_id' ),
                                array( $cond, 'rev_parent_id' => null ), __METHOD__ );
                        # Go through and update rev_parent_id from these rows.
                        # Assume that the previous revision of the title was
                        # the original previous revision of the title when the
                        # edit was made...
                        foreach ( $res as $row ) {
                                # First, check rows with the same timestamp other than this one
                                # with a smaller rev ID. The highest ID "wins". This avoids loops
                                # as timestamp can only decrease and never loops with IDs (from parent to parent)
                                $previousID = $db->selectField( 'revision', 'rev_id',
                                        array( 'rev_page' => $row->rev_page, 'rev_timestamp' => $row->rev_timestamp,
                                                "rev_id < " . intval( $row->rev_id ) ),
                                        __METHOD__,
                                        array( 'ORDER BY' => 'rev_id DESC' ) );
                                # If there are none, check the the highest ID with a lower timestamp
                                if ( !$previousID ) {
                                        # Get the highest older timestamp
                                        $lastTimestamp = $db->selectField( 'revision', 'rev_timestamp',
                                                array( 'rev_page' => $row->rev_page, "rev_timestamp < " . $db->addQuotes( $row->rev_timestamp ) ),
                                                __METHOD__,
                                                array( 'ORDER BY' => 'rev_timestamp DESC' ) );
                                        # If there is one, let the highest rev ID win
                                        if ( $lastTimestamp ) {
                                                $previousID = $db->selectField( 'revision', 'rev_id',
                                                        array( 'rev_page' => $row->rev_page, 'rev_timestamp' => $lastTimestamp ),
                                                        __METHOD__,
                                                        array( 'ORDER BY' => 'rev_id DESC' ) );
                                        }
                                }
                                $previousID = intval( $previousID );
                                if ( $previousID != $row->rev_parent_id )
                                        $changed++;
                                # Update the row...
                                $db->update( 'revision',
                                        array( 'rev_parent_id' => $previousID ),
                                        array( 'rev_id' => $row->rev_id ),
                                        __METHOD__ );
                                $count++;
                        }
                        $blockStart += $this->mBatchSize;
                        $blockEnd += $this->mBatchSize;
                        wfWaitForSlaves();
                }
                $this->output( "rev_parent_id population complete ... {$count} rows [{$changed} changed]\n" );
                return true;
        }
}

$maintClass = "PopulateParentId";
require_once( RUN_MAINTENANCE_IF_MAIN );