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                 if ( $wgMemc->get( $this->getEmptinessCacheKey() ) === 'true' ) {
 115                         return false; // queue is empty
 116                 }
 117
 118                 $dbw = $this->getMasterDB();
 119                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 120
 121                 $uuid = wfRandomString( 32 ); // pop attempt
 122                 $job = false; // job popped off
 123                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
 124                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 125                 try {
 126                         do { // retry when our row is invalid or deleted as a duplicate
 127                                 // Try to reserve a row in the DB...
 128                                 if ( $this->order === 'timestamp' ) { // oldest first
 129                                         $found = $this->claim( $uuid, 0, true );
 130                                 } else { // random first
 131                                         $rand  = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 132                                         $gte   = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 133                                         $found = $this->claim( $uuid, $rand, $gte )
 134                                                 || $this->claim( $uuid, $rand, !$gte ); // try both directions
 135                                 }
 136                                 // Check if we found a row to reserve...
 137                                 if ( !$found ) {
 138                                         $wgMemc->set( $this->getEmptinessCacheKey(), 'true', self::CACHE_TTL );
 139                                         break; // nothing to do
 140                                 }
 141                                 // Fetch any row that we just reserved...
 142                                 $row = $dbw->selectRow( 'job', '*',
 143                                         array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__ );
 144                                 // Check if another process deleted it as a duplicate
 145                                 if ( !$row ) {
 146                                         wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
 147                                         continue; // try again
 148                                 }
 149                                 // Get the job object from the row...
 150                                 $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 151                                 if ( !$title ) {
 152                                         $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 153                                         wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
 154                                         continue; // try again
 155                                 }
 156                                 $job = Job::factory( $row->job_cmd, $title,
 157                                         self::extractBlob( $row->job_params ), $row->job_id );
 158                                 // Delete any *other* duplicate jobs in the queue...
 159                                 if ( $job->ignoreDuplicates() && strlen( $row->job_sha1 ) ) {
 160                                         $dbw->delete( 'job',
 161                                                 array( 'job_sha1' => $row->job_sha1,
 162                                                         "job_id != {$dbw->addQuotes( $row->job_id )}" ),
 163                                                 __METHOD__
 164                                         );
 165                                 }
 166                                 break; // done
 167                         } while( true );
 168                 } catch ( DBError $e ) {
 169                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 170                         throw $e;
 171                 }
 172                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 173
 174                 return $job;
 175         }
 176
 177         /**
 178          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 179          * @param $uuid string 32 char hex string
 180          * @param $rand integer Random unsigned integer (31 bits)
 181          * @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
 182          * @return integer Number of affected rows
 183          */
 184         protected function claim( $uuid, $rand, $gte ) {
 185                 $dbw  = $this->getMasterDB();
 186                 $dir  = $gte ? 'ASC' : 'DESC';
 187                 $ineq = $gte ? '>=' : '<=';
 188                 if ( $dbw->getType() === 'mysql' ) {
 189                         // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 190                         // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 191                         // Oracle and Postgre have no such limitation. However, MySQL offers an
 192                         // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 193                         // The DB wrapper functions do not support this, so it's done manually.
 194                         $dbw->query( "UPDATE {$dbw->tableName( 'job' )}
 195                                 SET
 196                                         job_token = {$dbw->addQuotes( $uuid ) },
 197                                         job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}
 198                                 WHERE (
 199                                         job_cmd = {$dbw->addQuotes( $this->type )}
 200                                         AND job_token = {$dbw->addQuotes( '' )}
 201                                         AND job_random {$ineq} {$dbw->addQuotes( $rand )}
 202                                 ) ORDER BY job_random {$dir} LIMIT 1",
 203                                 __METHOD__
 204                         );
 205                 } else {
 206                         // Use a subquery to find the job, within an UPDATE to claim it.
 207                         // This uses as much of the DB wrapper functions as possible.
 208                         $dbw->update( 'job',
 209                                 array( 'job_token' => $uuid, 'job_token_timestamp' => $dbw->timestamp() ),
 210                                 array( 'job_id = (' .
 211                                         $dbw->selectSQLText( 'job', 'job_id',
 212                                                 array(
 213                                                         'job_cmd'   => $this->type,
 214                                                         'job_token' => '',
 215                                                         "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 216                                                 __METHOD__,
 217                                                 array( 'ORDER BY' => "job_random {$dir}", 'LIMIT' => 1 ) ) .
 218                                         ')'
 219                                 ),
 220                                 __METHOD__
 221                         );
 222                 }
 223                 return $dbw->affectedRows();
 224         }
 225
 226         /**
 227          * @see JobQueue::doAck()
 228          * @return Job|bool
 229          */
 230         protected function doAck( Job $job ) {
 231                 $dbw = $this->getMasterDB();
 232                 if ( $dbw->trxLevel() ) {
 233                         wfWarn( "Attempted to ack a job in a transaction; committing first." );
 234                         $dbw->commit(); // push existing transaction
 235                 }
 236
 237                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
 238                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 239                 try {
 240                         // Delete a row with a single DELETE without holding row locks over RTTs...
 241                         $dbw->delete( 'job', array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ) );
 242                 } catch ( Exception $e ) {
 243                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 244                         throw $e;
 245                 }
 246                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 247
 248                 return true;
 249         }
 250
 251         /**
 252          * @see JobQueue::doWaitForBackups()
 253          * @return void
 254          */
 255         protected function doWaitForBackups() {
 256                 wfWaitForSlaves();
 257         }
 258
 259         /**
 260          * @return DatabaseBase
 261          */
 262         protected function getSlaveDB() {
 263                 return wfGetDB( DB_SLAVE, array(), $this->wiki );
 264         }
 265
 266         /**
 267          * @return DatabaseBase
 268          */
 269         protected function getMasterDB() {
 270                 return wfGetDB( DB_MASTER, array(), $this->wiki );
 271         }
 272
 273         /**
 274          * @param $job Job
 275          * @return array
 276          */
 277         protected function insertFields( Job $job ) {
 278                 // Rows that describe the nature of the job
 279                 $descFields = array(
 280                         'job_cmd'       => $job->getType(),
 281                         'job_namespace' => $job->getTitle()->getNamespace(),
 282                         'job_title'     => $job->getTitle()->getDBkey(),
 283                         'job_params'    => self::makeBlob( $job->getParams() ),
 284                 );
 285                 // Additional job metadata
 286                 if ( $this->order === 'timestamp' ) { // oldest first
 287                         $random = time() - 1325376000; // seconds since "January 1, 2012"
 288                 } else { // random first
 289                         $random = mt_rand( 0, self::MAX_JOB_RANDOM );
 290                 }
 291                 $dbw = $this->getMasterDB();
 292                 $metaFields = array(
 293                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 294                         'job_timestamp' => $dbw->timestamp(),
 295                         'job_sha1'      => wfBaseConvert( sha1( serialize( $descFields ) ), 16, 36, 32 ),
 296                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 297                 );
 298                 return ( $descFields + $metaFields );
 299         }
 300
 301         /**
 302          * @return string
 303          */
 304         private function getEmptinessCacheKey() {
 305                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 306                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'isempty' );
 307         }
 308
 309         /**
 310          * @param $params
 311          * @return string
 312          */
 313         protected static function makeBlob( $params ) {
 314                 if ( $params !== false ) {
 315                         return serialize( $params );
 316                 } else {
 317                         return '';
 318                 }
 319         }
 320
 321         /**
 322          * @param $blob
 323          * @return bool|mixed
 324          */
 325         protected static function extractBlob( $blob ) {
 326                 if ( (string)$blob !== '' ) {
 327                         return unserialize( $blob );
 328                 } else {
 329                         return false;
 330                 }
 331         }
 332 }