purgeParserCache.php

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<?php
// @codeCoverageIgnoreStart
require_once __DIR__ . '/Maintenance.php';
// @codeCoverageIgnoreEnd
 
use MediaWiki\MainConfigNames;
use Wikimedia\Timestamp\ConvertibleTimestamp;
 
class PurgeParserCache extends Maintenance {
 
    private $lastProgress;
 
    private $lastTimestamp;
 
    private $tmpCount = 0;
    private $usleep = 0;
 
    public function __construct() {
        parent::__construct();
        $this->addDescription( "Remove old objects from the parser cache. " .
            "This only works when the parser cache is in an SQL database." );
        $this->addOption( 'expiredate', 'Delete objects expiring before this date.', false, true );
        $this->addOption(
            'age',
            'Delete objects created more than this many seconds ago, assuming ' .
                '$wgParserCacheExpireTime has remained consistent.',
            false,
            true );
        $this->addOption( 'dry-run', 'Perform a dry run, to verify age and date calculation.' );
        $this->addOption( 'msleep', 'Milliseconds to sleep between purge chunks of $wgUpdateRowsPerQuery.',
            false,
            true );
        $this->addOption(
            'tag',
            'Purge a single server only. This feature is designed for use by large wiki farms where ' .
                'one has to purge multiple servers concurrently in order to keep up with new writes. ' .
                'This requires using the SqlBagOStuff "servers" option in $wgObjectCaches.',
            false,
            true );
    }
 
    public function execute() {
        $inputDate = $this->getOption( 'expiredate' );
        $inputAge = $this->getOption( 'age' );
 
        if ( $inputDate !== null ) {
            $timestamp = strtotime( $inputDate );
        } elseif ( $inputAge !== null ) {
            $expireTime = (int)$this->getConfig()->get( MainConfigNames::ParserCacheExpireTime );
            $timestamp = time() + $expireTime - intval( $inputAge );
        } else {
            $this->fatalError( "Must specify either --expiredate or --age" );
        }
        $this->usleep = 1e3 * $this->getOption( 'msleep', 0 );
        $this->lastTimestamp = microtime( true );
 
        $humanDate = ConvertibleTimestamp::convert( TS_RFC2822, $timestamp );
        if ( $this->hasOption( 'dry-run' ) ) {
            $this->fatalError( "\nDry run mode, would delete objects having an expiry before " . $humanDate . "\n" );
        }
 
        $this->output( "Deleting objects expiring before " . $humanDate . "\n" );
 
        $pc = $this->getServiceContainer()->getParserCache()->getCacheStorage();
        $success = $pc->deleteObjectsExpiringBefore(
            $timestamp,
            [ $this, 'showProgressAndWait' ],
            INF,
            // Note that "0" can be a valid server tag, and must not be discarded or changed to null.
            $this->getOption( 'tag', null )
        );
        if ( !$success ) {
            $this->fatalError( "\nCannot purge this kind of parser cache." );
        }
        $this->showProgressAndWait( 100 );
        $this->output( "\nDone\n" );
    }
 
    public function showProgressAndWait( $percent ) {
        // Parser caches involve mostly-unthrottled writes of large blobs. This is sometimes prone
        // to replication lag. As such, while our purge queries are simple primary key deletes,
        // we want to avoid adding significant load to the replication stream, by being
        // proactively graceful with these sleeps between each batch.
        // The reason we don't explicitly wait for replication is that that would require the script
        // to be aware of cross-dc replicas, which we prefer not to, and waiting for replication
        // and confirmation latency might actually be *too* graceful and take so long that the
        // purge script would not be able to finish within 24 hours for large wiki farms.
        // (T150124).
        usleep( $this->usleep );
        $this->tmpCount++;
 
        $percentString = sprintf( "%.1f", $percent );
        if ( $percentString === $this->lastProgress ) {
            // Only print a line if we've progressed >= 0.1% since the last printed line.
            // This does not mean every 0.1% step is printed since we only run this callback
            // once after a deletion batch. How often and how many lines we print depends on the
            // batch size (SqlBagOStuff::deleteObjectsExpiringBefore, $wgUpdateRowsPerQuery),
            // and on how many table rows there are.
            return;
        }
        $now = microtime( true );
        $sec = sprintf( "%.1f", $now - $this->lastTimestamp );
 
        // Give a sense of how much time is spent in the delete operations vs the sleep time,
        // by recording the number of iterations we've completed since the last progress update.
        $this->output( "... {$percentString}% done (+{$this->tmpCount} iterations in {$sec}s)\n" );
 
        $this->lastProgress = $percentString;
        $this->tmpCount = 0;
        $this->lastTimestamp = $now;
    }
}
 
// @codeCoverageIgnoreStart
$maintClass = PurgeParserCache::class;
require_once RUN_MAINTENANCE_IF_MAIN;
// @codeCoverageIgnoreEnd