includes/job/JobQueueDB.php

   1 <?php
   2 /**
   3  * Database-backed job queue code.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @author Aaron Schulz
  22  */
  23
  24 /**
  25  * Class to handle job queues stored in the DB
  26  *
  27  * @ingroup JobQueue
  28  * @since 1.20
  29  */
  30 class JobQueueDB extends JobQueue {
  31         const CACHE_TTL      = 30; // integer; seconds
  32         const MAX_JOB_RANDOM = 2147483647; // 2^31 - 1; used for job_random
  33
  34         /**
  35          * @see JobQueue::doIsEmpty()
  36          * @return bool
  37          */
  38         protected function doIsEmpty() {
  39                 global $wgMemc;
  40
  41                 $key = $this->getEmptinessCacheKey();
  42
  43                 $isEmpty = $wgMemc->get( $key );
  44                 if ( $isEmpty === 'true' ) {
  45                         return true;
  46                 } elseif ( $isEmpty === 'false' ) {
  47                         return false;
  48                 }
  49
  50                 $found = $this->getSlaveDB()->selectField(
  51                         'job', '1', array( 'job_cmd' => $this->type ), __METHOD__
  52                 );
  53
  54                 $wgMemc->add( $key, $found ? 'false' : 'true', self::CACHE_TTL );
  55         }
  56
  57         /**
  58          * @see JobQueue::doBatchPush()
  59          * @return bool
  60          */
  61         protected function doBatchPush( array $jobs, $flags ) {
  62                 if ( count( $jobs ) ) {
  63                         $dbw = $this->getMasterDB();
  64
  65                         $rows = array();
  66                         foreach ( $jobs as $job ) {
  67                                 $rows[] = $this->insertFields( $job );
  68                         }
  69                         $atomic = ( $flags & self::QoS_Atomic );
  70                         $key    = $this->getEmptinessCacheKey();
  71                         $ttl    = self::CACHE_TTL;
  72
  73                         $dbw->onTransactionIdle( function() use ( $dbw, $rows, $atomic, $key, $ttl ) {
  74                                 global $wgMemc;
  75
  76                                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
  77                                 if ( $atomic ) {
  78                                         $dbw->begin(); // wrap all the job additions in one transaction
  79                                 } else {
  80                                         $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
  81                                 }
  82                                 try {
  83                                         foreach ( array_chunk( $rows, 50 ) as $rowBatch ) { // avoid slave lag
  84                                                 $dbw->insert( 'job', $rowBatch, __METHOD__ );
  85                                         }
  86                                 } catch ( DBError $e ) {
  87                                         if ( $atomic ) {
  88                                                 $dbw->rollback();
  89                                         } else {
  90                                                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
  91                                         }
  92                                         throw $e;
  93                                 }
  94                                 if ( $atomic ) {
  95                                         $dbw->commit();
  96                                 } else {
  97                                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
  98                                 }
  99
 100                                 $wgMemc->set( $key, 'false', $ttl );
 101                         } );
 102                 }
 103
 104                 return true;
 105         }
 106
 107         /**
 108          * @see JobQueue::doPop()
 109          * @return Job|bool
 110          */
 111         protected function doPop() {
 112                 global $wgMemc;
 113
 114                 $uuid = wfRandomString( 32 ); // pop attempt
 115
 116                 $dbw = $this->getMasterDB();
 117                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 118
 119                 $job = false; // job popped off
 120                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
 121                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 122                 try {
 123                         do { // retry when our row is invalid or deleted as a duplicate
 124                                 $row = false; // row claimed
 125                                 $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 126                                 $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 127                                 // Try to reserve a DB row...
 128                                 if ( $this->claim( $uuid, $rand, $gte ) || $this->claim( $uuid, $rand, !$gte ) ) {
 129                                         // Fetch any row that we just reserved...
 130                                         $row = $dbw->selectRow( 'job', '*',
 131                                                 array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__ );
 132                                         // Check if another process deleted it as a duplicate
 133                                         if ( !$row ) {
 134                                                 wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
 135                                                 continue; // try again
 136                                         }
 137                                         // Get the job object from the row...
 138                                         $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 139                                         if ( !$title ) {
 140                                                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 141                                                 wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
 142                                                 continue; // try again
 143                                         }
 144                                         $job = Job::factory( $row->job_cmd, $title,
 145                                                 self::extractBlob( $row->job_params ), $row->job_id );
 146                                         // Delete any *other* duplicate jobs in the queue...
 147                                         if ( $job->ignoreDuplicates() && strlen( $row->job_sha1 ) ) {
 148                                                 $dbw->delete( 'job',
 149                                                         array( 'job_sha1' => $row->job_sha1,
 150                                                                 "job_id != {$dbw->addQuotes( $row->job_id )}" ),
 151                                                         __METHOD__
 152                                                 );
 153                                         }
 154                                 } else {
 155                                         $wgMemc->set( $this->getEmptinessCacheKey(), 'true', self::CACHE_TTL );
 156                                 }
 157                                 break; // done
 158                         } while( true );
 159                 } catch ( DBError $e ) {
 160                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 161                         throw $e;
 162                 }
 163                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 164
 165                 return $job;
 166         }
 167
 168         /**
 169          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 170          * @param $uuid string 32 char hex string
 171          * @param $rand integer Random unsigned integer (31 bits)
 172          * @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
 173          * @return integer Number of affected rows
 174          */
 175         protected function claim( $uuid, $rand, $gte ) {
 176                 $dbw  = $this->getMasterDB();
 177                 $dir  = $gte ? 'ASC' : 'DESC';
 178                 $ineq = $gte ? '>=' : '<=';
 179                 if ( $dbw->getType() === 'mysql' ) {
 180                         // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 181                         // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 182                         // Oracle and Postgre have no such limitation. However, MySQL offers an
 183                         // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 184                         // The DB wrapper functions do not support this, so it's done manually.
 185                         $dbw->query( "UPDATE {$dbw->tableName( 'job' )}
 186                                 SET
 187                                         job_token = {$dbw->addQuotes( $uuid ) },
 188                                         job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}
 189                                 WHERE (
 190                                         job_cmd = {$dbw->addQuotes( $this->type )}
 191                                         AND job_token = {$dbw->addQuotes( '' )}
 192                                         AND job_random {$ineq} {$dbw->addQuotes( $rand )}
 193                                 ) ORDER BY job_random {$dir} LIMIT 1",
 194                                 __METHOD__
 195                         );
 196                 } else {
 197                         // Use a subquery to find the job, within an UPDATE to claim it.
 198                         // This uses as much of the DB wrapper functions as possible.
 199                         $dbw->update( 'job',
 200                                 array( 'job_token' => $uuid, 'job_token_timestamp' => $dbw->timestamp() ),
 201                                 array( 'job_id = (' .
 202                                         $dbw->selectSQLText( 'job', 'job_id',
 203                                                 array(
 204                                                         'job_cmd'   => $this->type,
 205                                                         'job_token' => '',
 206                                                         "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 207                                                 __METHOD__,
 208                                                 array( 'ORDER BY' => "job_random {$dir}", 'LIMIT' => 1 ) ) .
 209                                         ')'
 210                                 ),
 211                                 __METHOD__
 212                         );
 213                 }
 214                 return $dbw->affectedRows();
 215         }
 216
 217         /**
 218          * @see JobQueue::doAck()
 219          * @return Job|bool
 220          */
 221         protected function doAck( Job $job ) {
 222                 $dbw = $this->getMasterDB();
 223                 if ( $dbw->trxLevel() ) {
 224                         wfWarn( "Attempted to ack a job in a transaction; committing first." );
 225                         $dbw->commit(); // push existing transaction
 226                 }
 227
 228                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
 229                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 230                 try {
 231                         // Delete a row with a single DELETE without holding row locks over RTTs...
 232                         $dbw->delete( 'job', array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ) );
 233                 } catch ( Exception $e ) {
 234                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 235                         throw $e;
 236                 }
 237                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 238
 239                 return true;
 240         }
 241
 242         /**
 243          * @see JobQueue::doWaitForBackups()
 244          * @return void
 245          */
 246         protected function doWaitForBackups() {
 247                 wfWaitForSlaves();
 248         }
 249
 250         /**
 251          * @return DatabaseBase
 252          */
 253         protected function getSlaveDB() {
 254                 return wfGetDB( DB_SLAVE, array(), $this->wiki );
 255         }
 256
 257         /**
 258          * @return DatabaseBase
 259          */
 260         protected function getMasterDB() {
 261                 return wfGetDB( DB_MASTER, array(), $this->wiki );
 262         }
 263
 264         /**
 265          * @param $job Job
 266          * @return array
 267          */
 268         protected function insertFields( Job $job ) {
 269                 // Rows that describe the nature of the job
 270                 $descFields = array(
 271                         'job_cmd'       => $job->getType(),
 272                         'job_namespace' => $job->getTitle()->getNamespace(),
 273                         'job_title'     => $job->getTitle()->getDBkey(),
 274                         'job_params'    => self::makeBlob( $job->getParams() ),
 275                 );
 276                 // Additional job metadata
 277                 $dbw = $this->getMasterDB();
 278                 $metaFields = array(
 279                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 280                         'job_timestamp' => $dbw->timestamp(),
 281                         'job_sha1'      => wfBaseConvert( sha1( serialize( $descFields ) ), 16, 36, 32 ),
 282                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 283                 );
 284                 return ( $descFields + $metaFields );
 285         }
 286
 287         /**
 288          * @return string
 289          */
 290         private function getEmptinessCacheKey() {
 291                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 292                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'isempty' );
 293         }
 294
 295         /**
 296          * @param $params
 297          * @return string
 298          */
 299         protected static function makeBlob( $params ) {
 300                 if ( $params !== false ) {
 301                         return serialize( $params );
 302                 } else {
 303                         return '';
 304                 }
 305         }
 306
 307         /**
 308          * @param $blob
 309          * @return bool|mixed
 310          */
 311         protected static function extractBlob( $blob ) {
 312                 if ( (string)$blob !== '' ) {
 313                         return unserialize( $blob );
 314                 } else {
 315                         return false;
 316                 }
 317         }
 318 }