RefreshLinksJob.php

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<?php
use MediaWiki\Deferred\LinksUpdate\LinksUpdate;
use MediaWiki\Deferred\RefreshSecondaryDataUpdate;
use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MainConfigNames;
use MediaWiki\MediaWikiServices;
use MediaWiki\Page\PageAssertionException;
use MediaWiki\Page\PageIdentity;
use MediaWiki\Parser\ParserCache;
use MediaWiki\Parser\ParserOutput;
use MediaWiki\Revision\RevisionRecord;
use MediaWiki\Revision\RevisionRenderer;
use MediaWiki\Revision\SlotRecord;
use MediaWiki\Title\Title;
use MediaWiki\User\User;
use MediaWiki\WikiMap\WikiMap;
use Wikimedia\Rdbms\IDBAccessObject;
use Wikimedia\Stats\StatsFactory;
 
class RefreshLinksJob extends Job {
    private const NORMAL_MAX_LAG = 10;
    private const LAG_WAIT_TIMEOUT = 15;
 
    public function __construct( PageIdentity $page, array $params ) {
        if ( empty( $params['pages'] ) && !$page->canExist() ) {
            // BC with the Title class
            throw new PageAssertionException(
                'The given PageIdentity {pageIdentity} does not represent a proper page',
                [ 'pageIdentity' => $page ]
            );
        }
 
        parent::__construct( 'refreshLinks', $page, $params );
        // Avoid the overhead of de-duplication when it would be pointless
        $this->removeDuplicates = (
            // Ranges rarely will line up
            !isset( $params['range'] ) &&
            // Multiple pages per job make matches unlikely
            !( isset( $params['pages'] ) && count( $params['pages'] ) != 1 )
        );
        $this->params += [ 'causeAction' => 'RefreshLinksJob', 'causeAgent' => 'unknown' ];
        // Tell JobRunner to not automatically wrap run() in a transaction round.
        // Each runForTitle() call will manage its own rounds in order to run DataUpdates
        // and to avoid contention as well.
        $this->executionFlags |= self::JOB_NO_EXPLICIT_TRX_ROUND;
    }
 
    public static function newPrioritized( PageIdentity $page, array $params ) {
        $job = new self( $page, $params );
        $job->command = 'refreshLinksPrioritized';
 
        return $job;
    }
 
    public static function newDynamic( PageIdentity $page, array $params ) {
        $job = new self( $page, $params );
        $job->command = 'refreshLinksDynamic';
 
        return $job;
    }
 
    public function run() {
        $ok = true;
 
        if ( !empty( $this->params['recursive'] ) ) {
            // Job to update all (or a range of) backlink pages for a page
 
            // When the base job branches, wait for the replica DBs to catch up to the primary.
            // From then on, we know that any template changes at the time the base job was
            // enqueued will be reflected in backlink page parses when the leaf jobs run.
            $services = MediaWikiServices::getInstance();
            if ( !isset( $this->params['range'] ) ) {
                $lbFactory = $services->getDBLoadBalancerFactory();
                if ( !$lbFactory->waitForReplication( [
                    'timeout' => self::LAG_WAIT_TIMEOUT
                ] ) ) {
                    // only try so hard, keep going with what we have
                    $stats = $services->getStatsFactory();
                    $stats->getCounter( 'refreshlinks_warnings_total' )
                        ->setLabel( 'reason', 'lag_wait_failed' )
                        ->copyToStatsdAt( 'refreshlinks_warning.lag_wait_failed' )
                        ->increment();
                }
            }
            // Carry over information for de-duplication
            $extraParams = $this->getRootJobParams();
            $extraParams['triggeredRecursive'] = true;
            // Carry over cause information for logging
            $extraParams['causeAction'] = $this->params['causeAction'];
            $extraParams['causeAgent'] = $this->params['causeAgent'];
            // Convert this into no more than $wgUpdateRowsPerJob RefreshLinks per-title
            // jobs and possibly a recursive RefreshLinks job for the rest of the backlinks
            $jobs = BacklinkJobUtils::partitionBacklinkJob(
                $this,
                $services->getMainConfig()->get( MainConfigNames::UpdateRowsPerJob ),
                1, // job-per-title
                [ 'params' => $extraParams ]
            );
            $services->getJobQueueGroup()->push( $jobs );
 
        } elseif ( isset( $this->params['pages'] ) ) {
            // Job to update link tables for a set of titles
            foreach ( $this->params['pages'] as [ $ns, $dbKey ] ) {
                $title = Title::makeTitleSafe( $ns, $dbKey );
                if ( $title && $title->canExist() ) {
                    $ok = $this->runForTitle( $title ) && $ok;
                } else {
                    $ok = false;
                    $this->setLastError( "Invalid title ($ns,$dbKey)." );
                }
            }
 
        } else {
            // Job to update link tables for a given title
            $ok = $this->runForTitle( $this->title );
        }
 
        return $ok;
    }
 
    protected function runForTitle( PageIdentity $pageIdentity ) {
        $services = MediaWikiServices::getInstance();
        $stats = $services->getStatsFactory();
        $renderer = $services->getRevisionRenderer();
        $parserCache = $services->getParserCache();
        $lbFactory = $services->getDBLoadBalancerFactory();
        $ticket = $lbFactory->getEmptyTransactionTicket( __METHOD__ );
 
        // Load the page from the primary DB
        $page = $services->getWikiPageFactory()->newFromTitle( $pageIdentity );
        $page->loadPageData( IDBAccessObject::READ_LATEST );
 
        if ( !$page->exists() ) {
            // Probably due to concurrent deletion or renaming of the page
            $logger = LoggerFactory::getInstance( 'RefreshLinksJob' );
            $logger->warning(
                'The page does not exist. Perhaps it was deleted?',
                [
                    'page_title' => $this->title->getPrefixedDBkey(),
                    'job_params' => $this->getParams(),
                    'job_metadata' => $this->getMetadata()
                ]
            );
            $this->incrementFailureCounter( $stats, 'page_not_found' );
 
            // retry later to handle unlucky race condition
            return false;
        }
 
        // Serialize link update job by page ID so they see each others' changes.
        // The page ID and latest revision ID will be queried again after the lock
        // is acquired to bail if they are changed from that of loadPageData() above.
        // Serialize links updates by page ID so they see each others' changes
        $dbw = $lbFactory->getPrimaryDatabase();
        $scopedLock = LinksUpdate::acquirePageLock( $dbw, $page->getId(), 'job' );
        if ( $scopedLock === null ) {
            // Another job is already updating the page, likely for a prior revision (T170596)
            $this->setLastError( 'LinksUpdate already running for this page, try again later.' );
            $this->incrementFailureCounter( $stats, 'lock_failure' );
 
            // retry later when overlapping job for previous rev is done
            return false;
        }
 
        if ( $this->isAlreadyRefreshed( $page ) ) {
            // this job has been superseded, e.g. by overlapping recursive job
            // for a different template edit, or by direct edit or purge.
            $stats->getCounter( 'refreshlinks_superseded_updates_total' )
                ->copyToStatsdAt( 'refreshlinks_outcome.good_update_superseded' )
                ->increment();
            // treat as success
            return true;
        }
 
        // Parse during a fresh transaction round for better read consistency
        $lbFactory->beginPrimaryChanges( __METHOD__ );
        $output = $this->getParserOutput( $renderer, $parserCache, $page, $stats );
        $options = $this->getDataUpdateOptions();
        $lbFactory->commitPrimaryChanges( __METHOD__ );
 
        if ( !$output ) {
            // probably raced out.
            // Specific refreshlinks_outcome metric sent by getCurrentRevisionIfUnchanged().
            // Don't retry job.
            return true;
        }
 
        // Tell DerivedPageDataUpdater to use this parser output
        $options['known-revision-output'] = $output;
        // Execute corresponding DataUpdates immediately
        $page->doSecondaryDataUpdates( $options );
        InfoAction::invalidateCache( $page );
 
        // NOTE: Since 2019 (f588586e) this no longer saves the new ParserOutput to the ParserCache!
        //       This means the page will have to be rendered on-the-fly when it is next viewed.
        //       This is to avoid spending limited ParserCache capacity on rarely visited pages.
        // TODO: Save the ParserOutput to ParserCache by calling WikiPage::updateParserCache()
        //       for pages that are likely to benefit (T327162).
 
        // Commit any writes here in case this method is called in a loop.
        // In that case, the scoped lock will fail to be acquired.
        $lbFactory->commitAndWaitForReplication( __METHOD__, $ticket );
 
        return true;
    }
 
    private function getLagAwareRootTimestamp() {
        // Get the timestamp of the change that triggered this job
        $rootTimestamp = $this->params['rootJobTimestamp'] ?? null;
        if ( $rootTimestamp === null ) {
            return null;
        }
 
        if ( !empty( $this->params['isOpportunistic'] ) ) {
            // Neither clock skew nor DB snapshot/replica DB lag matter much for
            // such updates; focus on reusing the (often recently updated) cache
            $lagAwareTimestamp = $rootTimestamp;
        } else {
            // For transclusion updates, the template changes must be reflected
            $lagAwareTimestamp = wfTimestamp(
                TS_MW,
                (int)wfTimestamp( TS_UNIX, $rootTimestamp ) + self::NORMAL_MAX_LAG
            );
        }
 
        return $lagAwareTimestamp;
    }
 
    private function isAlreadyRefreshed( WikiPage $page ) {
        $lagAwareTimestamp = $this->getLagAwareRootTimestamp();
 
        return ( $lagAwareTimestamp !== null && $page->getLinksTimestamp() > $lagAwareTimestamp );
    }
 
    private function shouldGenerateHTMLOnEdit( RevisionRecord $revision ): bool {
        $services = MediaWikiServices::getInstance();
        foreach ( $revision->getSlots()->getSlotRoles() as $role ) {
            $slot = $revision->getSlots()->getSlot( $role );
            $contentHandler = $services->getContentHandlerFactory()->getContentHandler( $slot->getModel() );
            if ( $contentHandler->generateHTMLOnEdit() ) {
                return true;
            }
        }
        return false;
    }
 
    private function getParserOutput(
        RevisionRenderer $renderer,
        ParserCache $parserCache,
        WikiPage $page,
        StatsFactory $stats
    ) {
        $revision = $this->getCurrentRevisionIfUnchanged( $page, $stats );
        if ( !$revision ) {
            // race condition?
            return null;
        }
 
        $cachedOutput = $this->getParserOutputFromCache( $parserCache, $page, $revision, $stats );
        $statsCounter = $stats->getCounter( 'refreshlinks_parsercache_operations_total' );
 
        if ( $cachedOutput && $this->canUseParserOutputFromCache( $cachedOutput, $revision ) ) {
            $statsCounter
                ->setLabel( 'status', 'cache_hit' )
                ->setLabel( 'html_changed', 'n/a' )
                ->copyToStatsdAt( 'refreshlinks.parser_cached' )
                ->increment();
 
            return $cachedOutput;
        }
 
        $causeAction = $this->params['causeAction'] ?? 'RefreshLinksJob';
        $parserOptions = $page->makeParserOptions( 'canonical' );
 
        // T371713: Temporary statistics collection code to determine
        // feasibility of Parsoid selective update
        $sampleRate = MediaWikiServices::getInstance()->getMainConfig()->get(
            MainConfigNames::ParsoidSelectiveUpdateSampleRate
        );
        $doSample = $sampleRate && mt_rand( 1, $sampleRate ) === 1;
        if ( $doSample && $cachedOutput === null ) {
            // In order to collect accurate statistics, check for
            // a dirty copy in the cache even if we wouldn't have
            // to otherwise.
            $cachedOutput = $parserCache->getDirty( $page, $parserOptions ) ?: null;
        }
 
        $renderedRevision = $renderer->getRenderedRevision(
            $revision,
            $parserOptions,
            null,
            [
                'audience' => $revision::RAW,
                'causeAction' => $causeAction,
                // Providing a previous parse potentially allows for
                // selective updates
                'previous-output' => $cachedOutput,
            ]
        );
 
        $parseTimestamp = wfTimestampNow(); // timestamp that parsing started
        $output = $renderedRevision->getRevisionParserOutput( [
            // To avoid duplicate parses, this must match DerivedPageDataUpdater::shouldGenerateHTMLOnEdit() (T301309)
            'generate-html' => $this->shouldGenerateHTMLOnEdit( $revision )
        ] );
        $output->setCacheTime( $parseTimestamp ); // notify LinksUpdate::doUpdate()
        // T371713: Temporary statistics collection code to determine
        // feasibility of Parsoid selective update
        if ( $doSample ) {
            $content = $revision->getContent( SlotRecord::MAIN );
            $labels = [
                'source' => 'RefreshLinksJob',
                'type' => $cachedOutput === null ? 'full' : 'selective',
                'reason' => $causeAction,
                'parser' => $parserOptions->getUseParsoid() ? 'parsoid' : 'legacy',
                'opportunistic' => empty( $this->params['isOpportunistic'] ) ? 'false' : 'true',
                'wiki' => WikiMap::getCurrentWikiId(),
                'model' => $content ? $content->getModel() : 'unknown',
            ];
            $stats
                ->getCounter( 'ParserCache_selective_total' )
                ->setLabels( $labels )
                ->increment();
            $stats
                ->getCounter( 'ParserCache_selective_cpu_seconds' )
                ->setLabels( $labels )
                ->incrementBy( $output->getTimeProfile( 'cpu' ) );
        }
 
        // Collect stats on parses that don't actually change the page content.
        // In that case, we could abort here, and perhaps we could also avoid
        // triggering CDN purges (T369898).
        if ( !$cachedOutput ) {
            // There was no cached output
            $htmlChanged = 'unknown';
        } elseif ( $cachedOutput->getRawText() === $output->getRawText() ) {
            // We have cached output, but we couldn't be sure that it was still good.
            // So we parsed again, but the result turned out to be the same HTML as
            // before.
            $htmlChanged = 'no';
        } else {
            // Re-parsing yielded HTML different from the cached output.
            $htmlChanged = 'yes';
        }
 
        $statsCounter
            ->setLabel( 'status', 'cache_miss' )
            ->setLabel( 'html_changed', $htmlChanged )
            ->copyToStatsdAt( 'refreshlinks.parser_uncached' )
            ->increment();
 
        return $output;
    }
 
    private function getCurrentRevisionIfUnchanged(
        WikiPage $page,
        StatsFactory $stats
    ) {
        $title = $page->getTitle();
        // Get the latest ID since acquirePageLock() in runForTitle() flushed the transaction.
        // This is used to detect edits/moves after loadPageData() but before the scope lock.
        // The works around the chicken/egg problem of determining the scope lock key name
        $latest = $title->getLatestRevID( IDBAccessObject::READ_LATEST );
 
        $triggeringRevisionId = $this->params['triggeringRevisionId'] ?? null;
        if ( $triggeringRevisionId && $triggeringRevisionId !== $latest ) {
            // This job is obsolete and one for the latest revision will handle updates
            $this->incrementFailureCounter( $stats, 'rev_not_current' );
            $this->setLastError( "Revision $triggeringRevisionId is not current" );
            return null;
        }
 
        // Load the current revision. Note that $page should have loaded with READ_LATEST.
        // This instance will be reused in WikiPage::doSecondaryDataUpdates() later on.
        $revision = $page->getRevisionRecord();
        if ( !$revision ) {
            // revision just got deleted?
            $this->incrementFailureCounter( $stats, 'rev_not_found' );
            $this->setLastError( "Revision not found for {$title->getPrefixedDBkey()}" );
            return null;
 
        } elseif ( $revision->getId() !== $latest || $revision->getPageId() !== $page->getId() ) {
            // Do not clobber over newer updates with older ones. If all jobs where FIFO and
            // serialized, it would be OK to update links based on older revisions since it
            // would eventually get to the latest. Since that is not the case (by design),
            // only update the link tables to a state matching the current revision's output.
            $this->incrementFailureCounter( $stats, 'rev_not_current' );
            $this->setLastError( "Revision {$revision->getId()} is not current" );
 
            return null;
        }
 
        return $revision;
    }
 
    private function getParserOutputFromCache(
        ParserCache $parserCache,
        WikiPage $page,
        RevisionRecord $currentRevision,
        StatsFactory $stats
    ): ?ParserOutput {
        // Parsoid can do selective updates, so it is always worth the I/O
        // to check for a previous parse.
        $parserOptions = $page->makeParserOptions( 'canonical' );
        if ( $parserOptions->getUseParsoid() ) {
            return $parserCache->getDirty( $page, $parserOptions ) ?: null;
        }
        // If page_touched changed after this root job, then it is likely that
        // any views of the pages already resulted in re-parses which are now in
        // cache. The cache can be reused to avoid expensive parsing in some cases.
        $rootTimestamp = $this->params['rootJobTimestamp'] ?? null;
        if ( $rootTimestamp !== null ) {
            $opportunistic = !empty( $this->params['isOpportunistic'] );
            if ( $page->getTouched() >= $rootTimestamp || $opportunistic ) {
                // Cache is suspected to be up-to-date so it's worth the I/O of checking.
                // We call canUseParserOutputFromCache() later to check if it's usable.
                return $parserCache->getDirty( $page, $parserOptions ) ?: null;
            }
        }
 
        return null;
    }
 
    private function canUseParserOutputFromCache(
        ParserOutput $cachedOutput,
        RevisionRecord $currentRevision
    ) {
        // As long as the cache rev ID matches the current rev ID and it reflects
        // the job's triggering change, then it is usable.
        return $cachedOutput->getCacheRevisionId() == $currentRevision->getId()
            && $cachedOutput->getCacheTime() >= $this->getLagAwareRootTimestamp();
    }
 
    private function incrementFailureCounter( StatsFactory $stats, $reason ): void {
        $stats->getCounter( 'refreshlinks_failures_total' )
            ->setLabel( 'reason', $reason )
            ->copyToStatsdAt( "refreshlinks_outcome.bad_$reason" )
            ->increment();
    }
 
    private function getDataUpdateOptions() {
        $options = [
            'recursive' => !empty( $this->params['useRecursiveLinksUpdate'] ),
            // Carry over cause so the update can do extra logging
            'causeAction' => $this->params['causeAction'],
            'causeAgent' => $this->params['causeAgent']
        ];
        if ( !empty( $this->params['triggeringUser'] ) ) {
            $userInfo = $this->params['triggeringUser'];
            if ( $userInfo['userId'] ) {
                $options['triggeringUser'] = User::newFromId( $userInfo['userId'] );
            } else {
                // Anonymous, use the username
                $options['triggeringUser'] = User::newFromName( $userInfo['userName'], false );
            }
        }
 
        return $options;
    }
 
    public function getDeduplicationInfo() {
        $info = parent::getDeduplicationInfo();
        unset( $info['causeAction'] );
        unset( $info['causeAgent'] );
        if ( is_array( $info['params'] ) ) {
            // For per-pages jobs, the job title is that of the template that changed
            // (or similar), so remove that since it ruins duplicate detection
            if ( isset( $info['params']['pages'] ) ) {
                unset( $info['namespace'] );
                unset( $info['title'] );
            }
        }
 
        return $info;
    }
 
    public function workItemCount() {
        if ( !empty( $this->params['recursive'] ) ) {
            return 0; // nothing actually refreshed
        } elseif ( isset( $this->params['pages'] ) ) {
            return count( $this->params['pages'] );
        }
 
        return 1; // one title
    }
}