[JobQueue] Added missing delete query.

[mediawiki.git] / includes / job / JobQueueDB.php

<?php
/**
 * Database-backed job queue code.
 *
 * 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
 * @author Aaron Schulz
 */

/**
 * Class to handle job queues stored in the DB
 *
 * @ingroup JobQueue
 * @since 1.21
 */
class JobQueueDB extends JobQueue {
        const CACHE_TTL      = 300; // integer; seconds to cache queue information
        const MAX_AGE_PRUNE  = 604800; // integer; seconds a job can live once claimed
        const MAX_ATTEMPTS   = 3; // integer; number of times to try a job
        const MAX_JOB_RANDOM = 2147483647; // integer; 2^31 - 1, used for job_random

        /**
         * @see JobQueue::doIsEmpty()
         * @return bool
         */
        protected function doIsEmpty() {
                global $wgMemc;

                $key = $this->getEmptinessCacheKey();

                $isEmpty = $wgMemc->get( $key );
                if ( $isEmpty === 'true' ) {
                        return true;
                } elseif ( $isEmpty === 'false' ) {
                        return false;
                }

                $found = $this->getSlaveDB()->selectField(
                        'job', '1', array( 'job_cmd' => $this->type ), __METHOD__
                );

                $wgMemc->add( $key, $found ? 'false' : 'true', self::CACHE_TTL );
        }

        /**
         * @see JobQueue::doBatchPush()
         * @return bool
         */
        protected function doBatchPush( array $jobs, $flags ) {
                if ( count( $jobs ) ) {
                        $dbw = $this->getMasterDB();

                        $rows = array();
                        foreach ( $jobs as $job ) {
                                $rows[] = $this->insertFields( $job );
                        }
                        $atomic = ( $flags & self::QoS_Atomic );
                        $key    = $this->getEmptinessCacheKey();
                        $ttl    = self::CACHE_TTL;

                        $dbw->onTransactionIdle( function() use ( $dbw, $rows, $atomic, $key, $ttl ) {
                                global $wgMemc;

                                $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
                                if ( $atomic ) {
                                        $dbw->begin(); // wrap all the job additions in one transaction
                                } else {
                                        $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
                                }
                                try {
                                        foreach ( array_chunk( $rows, 50 ) as $rowBatch ) { // avoid slave lag
                                                $dbw->insert( 'job', $rowBatch, __METHOD__ );
                                        }
                                } catch ( DBError $e ) {
                                        if ( $atomic ) {
                                                $dbw->rollback();
                                        } else {
                                                $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
                                        }
                                        throw $e;
                                }
                                if ( $atomic ) {
                                        $dbw->commit();
                                } else {
                                        $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
                                }

                                $wgMemc->set( $key, 'false', $ttl ); // queue is not empty
                        } );
                }

                return true;
        }

        /**
         * @see JobQueue::doPop()
         * @return Job|bool
         */
        protected function doPop() {
                global $wgMemc;

                if ( $wgMemc->get( $this->getEmptinessCacheKey() ) === 'true' ) {
                        return false; // queue is empty
                }

                $dbw = $this->getMasterDB();
                $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction

                $uuid = wfRandomString( 32 ); // pop attempt
                $job = false; // job popped off
                $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
                $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
                try {
                        // Occasionally recycle jobs back into the queue that have been claimed too long
                        if ( mt_rand( 0, 99 ) == 0 ) {
                                $this->recycleStaleJobs();
                        }
                        do { // retry when our row is invalid or deleted as a duplicate
                                // Try to reserve a row in the DB...
                                if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
                                        $row = $this->claimOldest( $uuid );
                                } else { // random first
                                        $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
                                        $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
                                        $row  = $this->claimRandom( $uuid, $rand, $gte );
                                        if ( !$row ) { // need to try the other direction
                                                $row = $this->claimRandom( $uuid, $rand, !$gte );
                                        }
                                }
                                // Check if we found a row to reserve...
                                if ( !$row ) {
                                        $wgMemc->set( $this->getEmptinessCacheKey(), 'true', self::CACHE_TTL );
                                        break; // nothing to do
                                }
                                // Get the job object from the row...
                                $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
                                if ( !$title ) {
                                        $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
                                        wfIncrStats( 'job-pop' );
                                        wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
                                        continue; // try again
                                }
                                $job = Job::factory( $row->job_cmd, $title,
                                        self::extractBlob( $row->job_params ), $row->job_id );
                                // Delete any *other* duplicate jobs in the queue...
                                if ( $job->ignoreDuplicates() && strlen( $row->job_sha1 ) ) {
                                        $dbw->delete( 'job',
                                                array( 'job_sha1' => $row->job_sha1,
                                                        "job_id != {$dbw->addQuotes( $row->job_id )}" ),
                                                __METHOD__
                                        );
                                        wfIncrStats( 'job-pop', $dbw->affectedRows() );
                                }
                                break; // done
                        } while( true );
                } catch ( DBError $e ) {
                        $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
                        throw $e;
                }
                $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()

                return $job;
        }

        /**
         * Reserve a row with a single UPDATE without holding row locks over RTTs...
         *
         * @param $uuid string 32 char hex string
         * @param $rand integer Random unsigned integer (31 bits)
         * @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
         * @return Row|false
         */
        protected function claimRandom( $uuid, $rand, $gte ) {
                $dbw  = $this->getMasterDB();
                $dir  = $gte ? 'ASC' : 'DESC';
                $ineq = $gte ? '>=' : '<=';

                $row = false; // the row acquired
                // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
                // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
                // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
                // be used here with MySQL.
                do {
                        $row = $dbw->selectRow( 'job', '*', // find a random job
                                array(
                                        'job_cmd'   => $this->type,
                                        'job_token' => '',
                                        "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
                                __METHOD__,
                                array( 'ORDER BY' => "job_random {$dir}" )
                        );
                        if ( $row ) { // claim the job
                                $dbw->update( 'job', // update by PK
                                        array(
                                                'job_token'           => $uuid,
                                                'job_token_timestamp' => $dbw->timestamp(),
                                                'job_attempts = job_attempts+1' ),
                                        array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
                                        __METHOD__
                                );
                                // This might get raced out by another runner when claiming the previously
                                // selected row. The use of job_random should minimize this problem, however.
                                if ( !$dbw->affectedRows() ) {
                                        $row = false; // raced out
                                }
                        } else {
                                break; // nothing to do
                        }
                } while ( !$row );

                return $row;
        }

        /**
         * Reserve a row with a single UPDATE without holding row locks over RTTs...
         *
         * @param $uuid string 32 char hex string
         * @return Row|false
         */
        protected function claimOldest( $uuid ) {
                $dbw  = $this->getMasterDB();

                $row = false; // the row acquired
                do {
                        if ( $dbw->getType() === 'mysql' ) {
                                // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
                                // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
                                // Oracle and Postgre have no such limitation. However, MySQL offers an
                                // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
                                $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
                                        "SET " .
                                                "job_token = {$dbw->addQuotes( $uuid ) }, " .
                                                "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
                                                "job_attempts = job_attempts+1 " .
                                        "WHERE ( " .
                                                "job_cmd = {$dbw->addQuotes( $this->type )} " .
                                                "AND job_token = {$dbw->addQuotes( '' )} " .
                                        ") ORDER BY job_id ASC LIMIT 1",
                                        __METHOD__
                                );
                        } else {
                                // Use a subquery to find the job, within an UPDATE to claim it.
                                // This uses as much of the DB wrapper functions as possible.
                                $dbw->update( 'job',
                                        array(
                                                'job_token'           => $uuid,
                                                'job_token_timestamp' => $dbw->timestamp(),
                                                'job_attempts = job_attempts+1' ),
                                        array( 'job_id = (' .
                                                $dbw->selectSQLText( 'job', 'job_id',
                                                        array( 'job_cmd' => $this->type, 'job_token' => '' ),
                                                        __METHOD__,
                                                        array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
                                                ')'
                                        ),
                                        __METHOD__
                                );
                        }
                        // Fetch any row that we just reserved...
                        if ( $dbw->affectedRows() ) {
                                $row = $dbw->selectRow( 'job', '*',
                                        array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
                                );
                                if ( !$row ) { // raced out by duplicate job removal
                                        wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
                                }
                        } else {
                                break; // nothing to do
                        }
                } while ( !$row );

                return $row;
        }

        /**
         * Recycle or destroy any jobs that have been claimed for too long
         *
         * @return integer Number of jobs recycled/deleted
         */
        protected function recycleStaleJobs() {
                $now   = time();
                $dbw   = $this->getMasterDB();
                $count = 0; // affected rows

                if ( $this->claimTTL > 0 ) { // re-try stale jobs...
                        $claimCutoff = $dbw->timestamp( $now - $this->claimTTL );
                        // Reset job_token for these jobs so that other runners will pick them up.
                        // Set the timestamp to the current time, as it is useful to now that the job
                        // was already tried before.
                        $dbw->update( 'job',
                                array(
                                        'job_token' => '',
                                        'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
                                array(
                                        'job_cmd' => $this->type,
                                        "job_token != {$dbw->addQuotes( '' )}", // was acquired
                                        "job_token_timestamp < {$dbw->addQuotes( $claimCutoff )}", // stale
                                        "job_attempts < {$dbw->addQuotes( self::MAX_ATTEMPTS )}" ),
                                __METHOD__
                        );
                        $count += $dbw->affectedRows();
                }

                // Just destroy stale jobs...
                $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
                $conds = array(
                        'job_cmd' => $this->type,
                        "job_token != {$dbw->addQuotes( '' )}", // was acquired
                        "job_token_timestamp < {$dbw->addQuotes( $pruneCutoff )}" // stale
                );
                if ( $this->claimTTL > 0 ) { // only prune jobs attempted too many times...
                        $conds[] = "job_attempts >= {$dbw->addQuotes( self::MAX_ATTEMPTS )}";
                }
                $dbw->delete( 'job', $conds, __METHOD__ );
                $count += $dbw->affectedRows();

                return $count;
        }

        /**
         * @see JobQueue::doAck()
         * @return Job|bool
         */
        protected function doAck( Job $job ) {
                $dbw = $this->getMasterDB();
                $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction

                $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
                $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
                try {
                        // Delete a row with a single DELETE without holding row locks over RTTs...
                        $dbw->delete( 'job', array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ) );
                } catch ( Exception $e ) {
                        $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
                        throw $e;
                }
                $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()

                return true;
        }

        /**
         * @see JobQueue::doWaitForBackups()
         * @return void
         */
        protected function doWaitForBackups() {
                wfWaitForSlaves();
        }

        /**
         * @return DatabaseBase
         */
        protected function getSlaveDB() {
                return wfGetDB( DB_SLAVE, array(), $this->wiki );
        }

        /**
         * @return DatabaseBase
         */
        protected function getMasterDB() {
                return wfGetDB( DB_MASTER, array(), $this->wiki );
        }

        /**
         * @param $job Job
         * @return array
         */
        protected function insertFields( Job $job ) {
                // Rows that describe the nature of the job
                $descFields = array(
                        'job_cmd'       => $job->getType(),
                        'job_namespace' => $job->getTitle()->getNamespace(),
                        'job_title'     => $job->getTitle()->getDBkey(),
                        'job_params'    => self::makeBlob( $job->getParams() ),
                );
                // Additional job metadata
                $dbw = $this->getMasterDB();
                $metaFields = array(
                        'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
                        'job_timestamp' => $dbw->timestamp(),
                        'job_sha1'      => wfBaseConvert( sha1( serialize( $descFields ) ), 16, 36, 32 ),
                        'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
                );
                return ( $descFields + $metaFields );
        }

        /**
         * @return string
         */
        private function getEmptinessCacheKey() {
                list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
                return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'isempty' );
        }

        /**
         * @param $params
         * @return string
         */
        protected static function makeBlob( $params ) {
                if ( $params !== false ) {
                        return serialize( $params );
                } else {
                        return '';
                }
        }

        /**
         * @param $blob
         * @return bool|mixed
         */
        protected static function extractBlob( $blob ) {
                if ( (string)$blob !== '' ) {
                        return unserialize( $blob );
                } else {
                        return false;
                }
        }
}