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;