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 1.21
  29  */
  30 class JobQueueDB extends JobQueue {
  31         const CACHE_TTL_SHORT = 30; // integer; seconds to cache info without re-validating
  32         const CACHE_TTL_LONG = 300; // integer; seconds to cache info that is kept up to date
  33         const MAX_AGE_PRUNE = 604800; // integer; seconds a job can live once claimed
  34         const MAX_JOB_RANDOM = 2147483647; // integer; 2^31 - 1, used for job_random
  35         const MAX_OFFSET = 255; // integer; maximum number of rows to skip
  36
  37         /** @var BagOStuff */
  38         protected $cache;
  39
  40         protected $cluster = false; // string; name of an external DB cluster
  41
  42         /**
  43          * Additional parameters include:
  44          *   - cluster : The name of an external cluster registered via LBFactory.
  45          *               If not specified, the primary DB cluster for the wiki will be used.
  46          *               This can be overridden with a custom cluster so that DB handles will
  47          *               be retrieved via LBFactory::getExternalLB() and getConnection().
  48          * @param $params array
  49          */
  50         protected function __construct( array $params ) {
  51                 global $wgMemc;
  52
  53                 parent::__construct( $params );
  54
  55                 $this->cluster = isset( $params['cluster'] ) ? $params['cluster'] : false;
  56                 // Make sure that we don't use the SQL cache, which would be harmful
  57                 $this->cache = ( $wgMemc instanceof SqlBagOStuff ) ? new EmptyBagOStuff() : $wgMemc;
  58         }
  59
  60         protected function supportedOrders() {
  61                 return array( 'random', 'timestamp', 'fifo' );
  62         }
  63
  64         protected function optimalOrder() {
  65                 return 'random';
  66         }
  67
  68         /**
  69          * @see JobQueue::doIsEmpty()
  70          * @return bool
  71          */
  72         protected function doIsEmpty() {
  73                 $key = $this->getCacheKey( 'empty' );
  74
  75                 $isEmpty = $this->cache->get( $key );
  76                 if ( $isEmpty === 'true' ) {
  77                         return true;
  78                 } elseif ( $isEmpty === 'false' ) {
  79                         return false;
  80                 }
  81
  82                 list( $dbr, $scope ) = $this->getSlaveDB();
  83                 $found = $dbr->selectField( // unclaimed job
  84                         'job', '1', array( 'job_cmd' => $this->type, 'job_token' => '' ), __METHOD__
  85                 );
  86                 $this->cache->add( $key, $found ? 'false' : 'true', self::CACHE_TTL_LONG );
  87
  88                 return !$found;
  89         }
  90
  91         /**
  92          * @see JobQueue::doGetSize()
  93          * @return integer
  94          */
  95         protected function doGetSize() {
  96                 $key = $this->getCacheKey( 'size' );
  97
  98                 $size = $this->cache->get( $key );
  99                 if ( is_int( $size ) ) {
 100                         return $size;
 101                 }
 102
 103                 list( $dbr, $scope ) = $this->getSlaveDB();
 104                 $size = (int)$dbr->selectField( 'job', 'COUNT(*)',
 105                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
 106                         __METHOD__
 107                 );
 108                 $this->cache->set( $key, $size, self::CACHE_TTL_SHORT );
 109
 110                 return $size;
 111         }
 112
 113         /**
 114          * @see JobQueue::doGetAcquiredCount()
 115          * @return integer
 116          */
 117         protected function doGetAcquiredCount() {
 118                 if ( $this->claimTTL <= 0 ) {
 119                         return 0; // no acknowledgements
 120                 }
 121
 122                 $key = $this->getCacheKey( 'acquiredcount' );
 123
 124                 $count = $this->cache->get( $key );
 125                 if ( is_int( $count ) ) {
 126                         return $count;
 127                 }
 128
 129                 list( $dbr, $scope ) = $this->getSlaveDB();
 130                 $count = (int)$dbr->selectField( 'job', 'COUNT(*)',
 131                         array( 'job_cmd' => $this->type, "job_token != {$dbr->addQuotes( '' )}" ),
 132                         __METHOD__
 133                 );
 134                 $this->cache->set( $key, $count, self::CACHE_TTL_SHORT );
 135
 136                 return $count;
 137         }
 138
 139         /**
 140          * @see JobQueue::doGetAbandonedCount()
 141          * @return integer
 142          * @throws MWException
 143          */
 144         protected function doGetAbandonedCount() {
 145                 global $wgMemc;
 146
 147                 if ( $this->claimTTL <= 0 ) {
 148                         return 0; // no acknowledgements
 149                 }
 150
 151                 $key = $this->getCacheKey( 'abandonedcount' );
 152
 153                 $count = $wgMemc->get( $key );
 154                 if ( is_int( $count ) ) {
 155                         return $count;
 156                 }
 157
 158                 list( $dbr, $scope ) = $this->getSlaveDB();
 159                 $count = (int)$dbr->selectField( 'job', 'COUNT(*)',
 160                         array(
 161                                 'job_cmd' => $this->type,
 162                                 "job_token != {$dbr->addQuotes( '' )}",
 163                                 "job_attempts >= " . $dbr->addQuotes( $this->maxTries )
 164                         ),
 165                         __METHOD__
 166                 );
 167                 $wgMemc->set( $key, $count, self::CACHE_TTL_SHORT );
 168
 169                 return $count;
 170         }
 171
 172         /**
 173          * @see JobQueue::doBatchPush()
 174          * @param array $jobs
 175          * @param $flags
 176          * @throws DBError|Exception
 177          * @return bool
 178          */
 179         protected function doBatchPush( array $jobs, $flags ) {
 180                 list( $dbw, $scope ) = $this->getMasterDB();
 181
 182                 $that = $this;
 183                 $method = __METHOD__;
 184                 $dbw->onTransactionIdle(
 185                         function() use ( $dbw, $that, $jobs, $flags, $method, $scope ) {
 186                                 $that->doBatchPushInternal( $dbw, $jobs, $flags, $method );
 187                         }
 188                 );
 189
 190                 return true;
 191         }
 192
 193         /**
 194          * This function should *not* be called outside of JobQueueDB
 195          *
 196          * @param DatabaseBase $dbw
 197          * @param array $jobs
 198          * @param int $flags
 199          * @param string $method
 200          * @return boolean
 201          * @throws type
 202          */
 203         public function doBatchPushInternal( DatabaseBase $dbw, array $jobs, $flags, $method ) {
 204                 if ( !count( $jobs ) ) {
 205                         return true;
 206                 }
 207
 208                 $rowSet = array(); // (sha1 => job) map for jobs that are de-duplicated
 209                 $rowList = array(); // list of jobs for jobs that are are not de-duplicated
 210                 foreach ( $jobs as $job ) {
 211                         $row = $this->insertFields( $job );
 212                         if ( $job->ignoreDuplicates() ) {
 213                                 $rowSet[$row['job_sha1']] = $row;
 214                         } else {
 215                                 $rowList[] = $row;
 216                         }
 217                 }
 218
 219                 if ( $flags & self::QOS_ATOMIC ) {
 220                         $dbw->begin( $method ); // wrap all the job additions in one transaction
 221                 }
 222                 try {
 223                         // Strip out any duplicate jobs that are already in the queue...
 224                         if ( count( $rowSet ) ) {
 225                                 $res = $dbw->select( 'job', 'job_sha1',
 226                                         array(
 227                                                 // No job_type condition since it's part of the job_sha1 hash
 228                                                 'job_sha1' => array_keys( $rowSet ),
 229                                                 'job_token' => '' // unclaimed
 230                                         ),
 231                                         $method
 232                                 );
 233                                 foreach ( $res as $row ) {
 234                                         wfDebug( "Job with hash '{$row->job_sha1}' is a duplicate.\n" );
 235                                         unset( $rowSet[$row->job_sha1] ); // already enqueued
 236                                 }
 237                         }
 238                         // Build the full list of job rows to insert
 239                         $rows = array_merge( $rowList, array_values( $rowSet ) );
 240                         // Insert the job rows in chunks to avoid slave lag...
 241                         foreach ( array_chunk( $rows, 50 ) as $rowBatch ) {
 242                                 $dbw->insert( 'job', $rowBatch, $method );
 243                         }
 244                         JobQueue::incrStats( 'job-insert', $this->type, count( $rows ) );
 245                         JobQueue::incrStats( 'job-insert-duplicate', $this->type,
 246                                 count( $rowSet ) + count( $rowList ) - count( $rows ) );
 247                 } catch ( DBError $e ) {
 248                         if ( $flags & self::QOS_ATOMIC ) {
 249                                 $dbw->rollback( $method );
 250                         }
 251                         throw $e;
 252                 }
 253                 if ( $flags & self::QOS_ATOMIC ) {
 254                         $dbw->commit( $method );
 255                 }
 256
 257                 $this->cache->set( $this->getCacheKey( 'empty' ), 'false', JobQueueDB::CACHE_TTL_LONG );
 258
 259                 return true;
 260         }
 261
 262         /**
 263          * @see JobQueue::doPop()
 264          * @return Job|bool
 265          */
 266         protected function doPop() {
 267                 if ( $this->cache->get( $this->getCacheKey( 'empty' ) ) === 'true' ) {
 268                         return false; // queue is empty
 269                 }
 270
 271                 list( $dbw, $scope ) = $this->getMasterDB();
 272                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 273                 $autoTrx = $dbw->getFlag( DBO_TRX ); // get current setting
 274                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 275                 $scopedReset = new ScopedCallback( function() use ( $dbw, $autoTrx ) {
 276                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore old setting
 277                 } );
 278
 279                 $uuid = wfRandomString( 32 ); // pop attempt
 280                 $job = false; // job popped off
 281                 do { // retry when our row is invalid or deleted as a duplicate
 282                         // Try to reserve a row in the DB...
 283                         if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
 284                                 $row = $this->claimOldest( $uuid );
 285                         } else { // random first
 286                                 $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 287                                 $gte = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 288                                 $row = $this->claimRandom( $uuid, $rand, $gte );
 289                         }
 290                         // Check if we found a row to reserve...
 291                         if ( !$row ) {
 292                                 $this->cache->set( $this->getCacheKey( 'empty' ), 'true', self::CACHE_TTL_LONG );
 293                                 break; // nothing to do
 294                         }
 295                         JobQueue::incrStats( 'job-pop', $this->type );
 296                         // Get the job object from the row...
 297                         $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 298                         if ( !$title ) {
 299                                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 300                                 wfDebug( "Row has invalid title '{$row->job_title}'." );
 301                                 continue; // try again
 302                         }
 303                         $job = Job::factory( $row->job_cmd, $title,
 304                                 self::extractBlob( $row->job_params ), $row->job_id );
 305                         $job->metadata['id'] = $row->job_id;
 306                         $job->id = $row->job_id; // XXX: work around broken subclasses
 307                         break; // done
 308                 } while ( true );
 309
 310                 return $job;
 311         }
 312
 313         /**
 314          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 315          *
 316          * @param string $uuid 32 char hex string
 317          * @param $rand integer Random unsigned integer (31 bits)
 318          * @param bool $gte Search for job_random >= $random (otherwise job_random <= $random)
 319          * @return Row|false
 320          */
 321         protected function claimRandom( $uuid, $rand, $gte ) {
 322                 list( $dbw, $scope ) = $this->getMasterDB();
 323                 // Check cache to see if the queue has <= OFFSET items
 324                 $tinyQueue = $this->cache->get( $this->getCacheKey( 'small' ) );
 325
 326                 $row = false; // the row acquired
 327                 $invertedDirection = false; // whether one job_random direction was already scanned
 328                 // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
 329                 // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
 330                 // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
 331                 // be used here with MySQL.
 332                 do {
 333                         if ( $tinyQueue ) { // queue has <= MAX_OFFSET rows
 334                                 // For small queues, using OFFSET will overshoot and return no rows more often.
 335                                 // Instead, this uses job_random to pick a row (possibly checking both directions).
 336                                 $ineq = $gte ? '>=' : '<=';
 337                                 $dir = $gte ? 'ASC' : 'DESC';
 338                                 $row = $dbw->selectRow( 'job', '*', // find a random job
 339                                         array(
 340                                                 'job_cmd' => $this->type,
 341                                                 'job_token' => '', // unclaimed
 342                                                 "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 343                                         __METHOD__,
 344                                         array( 'ORDER BY' => "job_random {$dir}" )
 345                                 );
 346                                 if ( !$row && !$invertedDirection ) {
 347                                         $gte = !$gte;
 348                                         $invertedDirection = true;
 349                                         continue; // try the other direction
 350                                 }
 351                         } else { // table *may* have >= MAX_OFFSET rows
 352                                 // Bug 42614: "ORDER BY job_random" with a job_random inequality causes high CPU
 353                                 // in MySQL if there are many rows for some reason. This uses a small OFFSET
 354                                 // instead of job_random for reducing excess claim retries.
 355                                 $row = $dbw->selectRow( 'job', '*', // find a random job
 356                                         array(
 357                                                 'job_cmd' => $this->type,
 358                                                 'job_token' => '', // unclaimed
 359                                         ),
 360                                         __METHOD__,
 361                                         array( 'OFFSET' => mt_rand( 0, self::MAX_OFFSET ) )
 362                                 );
 363                                 if ( !$row ) {
 364                                         $tinyQueue = true; // we know the queue must have <= MAX_OFFSET rows
 365                                         $this->cache->set( $this->getCacheKey( 'small' ), 1, 30 );
 366                                         continue; // use job_random
 367                                 }
 368                         }
 369                         if ( $row ) { // claim the job
 370                                 $dbw->update( 'job', // update by PK
 371                                         array(
 372                                                 'job_token' => $uuid,
 373                                                 'job_token_timestamp' => $dbw->timestamp(),
 374                                                 'job_attempts = job_attempts+1' ),
 375                                         array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
 376                                         __METHOD__
 377                                 );
 378                                 // This might get raced out by another runner when claiming the previously
 379                                 // selected row. The use of job_random should minimize this problem, however.
 380                                 if ( !$dbw->affectedRows() ) {
 381                                         $row = false; // raced out
 382                                 }
 383                         } else {
 384                                 break; // nothing to do
 385                         }
 386                 } while ( !$row );
 387
 388                 return $row;
 389         }
 390
 391         /**
 392          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 393          *
 394          * @param string $uuid 32 char hex string
 395          * @return Row|false
 396          */
 397         protected function claimOldest( $uuid ) {
 398                 list( $dbw, $scope ) = $this->getMasterDB();
 399
 400                 $row = false; // the row acquired
 401                 do {
 402                         if ( $dbw->getType() === 'mysql' ) {
 403                                 // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 404                                 // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 405                                 // Oracle and Postgre have no such limitation. However, MySQL offers an
 406                                 // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 407                                 $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
 408                                         "SET " .
 409                                                 "job_token = {$dbw->addQuotes( $uuid ) }, " .
 410                                                 "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
 411                                                 "job_attempts = job_attempts+1 " .
 412                                         "WHERE ( " .
 413                                                 "job_cmd = {$dbw->addQuotes( $this->type )} " .
 414                                                 "AND job_token = {$dbw->addQuotes( '' )} " .
 415                                         ") ORDER BY job_id ASC LIMIT 1",
 416                                         __METHOD__
 417                                 );
 418                         } else {
 419                                 // Use a subquery to find the job, within an UPDATE to claim it.
 420                                 // This uses as much of the DB wrapper functions as possible.
 421                                 $dbw->update( 'job',
 422                                         array(
 423                                                 'job_token' => $uuid,
 424                                                 'job_token_timestamp' => $dbw->timestamp(),
 425                                                 'job_attempts = job_attempts+1' ),
 426                                         array( 'job_id = (' .
 427                                                 $dbw->selectSQLText( 'job', 'job_id',
 428                                                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
 429                                                         __METHOD__,
 430                                                         array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
 431                                                 ')'
 432                                         ),
 433                                         __METHOD__
 434                                 );
 435                         }
 436                         // Fetch any row that we just reserved...
 437                         if ( $dbw->affectedRows() ) {
 438                                 $row = $dbw->selectRow( 'job', '*',
 439                                         array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
 440                                 );
 441                                 if ( !$row ) { // raced out by duplicate job removal
 442                                         wfDebug( "Row deleted as duplicate by another process." );
 443                                 }
 444                         } else {
 445                                 break; // nothing to do
 446                         }
 447                 } while ( !$row );
 448
 449                 return $row;
 450         }
 451
 452         /**
 453          * @see JobQueue::doAck()
 454          * @param Job $job
 455          * @throws MWException
 456          * @return Job|bool
 457          */
 458         protected function doAck( Job $job ) {
 459                 if ( !isset( $job->metadata['id'] ) ) {
 460                         throw new MWException( "Job of type '{$job->getType()}' has no ID." );
 461                 }
 462
 463                 list( $dbw, $scope ) = $this->getMasterDB();
 464                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 465                 $autoTrx = $dbw->getFlag( DBO_TRX ); // get current setting
 466                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 467                 $scopedReset = new ScopedCallback( function() use ( $dbw, $autoTrx ) {
 468                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore old setting
 469                 } );
 470
 471                 // Delete a row with a single DELETE without holding row locks over RTTs...
 472                 $dbw->delete( 'job',
 473                         array( 'job_cmd' => $this->type, 'job_id' => $job->metadata['id'] ), __METHOD__ );
 474
 475                 return true;
 476         }
 477
 478         /**
 479          * @see JobQueue::doDeduplicateRootJob()
 480          * @param Job $job
 481          * @throws MWException
 482          * @return bool
 483          */
 484         protected function doDeduplicateRootJob( Job $job ) {
 485                 $params = $job->getParams();
 486                 if ( !isset( $params['rootJobSignature'] ) ) {
 487                         throw new MWException( "Cannot register root job; missing 'rootJobSignature'." );
 488                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 489                         throw new MWException( "Cannot register root job; missing 'rootJobTimestamp'." );
 490                 }
 491                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 492                 // Callers should call batchInsert() and then this function so that if the insert
 493                 // fails, the de-duplication registration will be aborted. Since the insert is
 494                 // deferred till "transaction idle", do the same here, so that the ordering is
 495                 // maintained. Having only the de-duplication registration succeed would cause
 496                 // jobs to become no-ops without any actual jobs that made them redundant.
 497                 list( $dbw, $scope ) = $this->getMasterDB();
 498                 $cache = $this->cache;
 499                 $dbw->onTransactionIdle( function() use ( $cache, $params, $key, $scope ) {
 500                         $timestamp = $cache->get( $key ); // current last timestamp of this job
 501                         if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 502                                 return true; // a newer version of this root job was enqueued
 503                         }
 504
 505                         // Update the timestamp of the last root job started at the location...
 506                         return $cache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 507                 } );
 508
 509                 return true;
 510         }
 511
 512         /**
 513          * @see JobQueue::doDelete()
 514          * @return bool
 515          */
 516         protected function doDelete() {
 517                 list( $dbw, $scope ) = $this->getMasterDB();
 518
 519                 $dbw->delete( 'job', array( 'job_cmd' => $this->type ) );
 520                 return true;
 521         }
 522
 523         /**
 524          * @see JobQueue::doWaitForBackups()
 525          * @return void
 526          */
 527         protected function doWaitForBackups() {
 528                 wfWaitForSlaves();
 529         }
 530
 531         /**
 532          * @return Array
 533          */
 534         protected function doGetPeriodicTasks() {
 535                 return array(
 536                         'recycleAndDeleteStaleJobs' => array(
 537                                 'callback' => array( $this, 'recycleAndDeleteStaleJobs' ),
 538                                 'period' => ceil( $this->claimTTL / 2 )
 539                         )
 540                 );
 541         }
 542
 543         /**
 544          * @return void
 545          */
 546         protected function doFlushCaches() {
 547                 foreach ( array( 'empty', 'size', 'acquiredcount' ) as $type ) {
 548                         $this->cache->delete( $this->getCacheKey( $type ) );
 549                 }
 550         }
 551
 552         /**
 553          * @see JobQueue::getAllQueuedJobs()
 554          * @return Iterator
 555          */
 556         public function getAllQueuedJobs() {
 557                 list( $dbr, $scope ) = $this->getSlaveDB();
 558                 return new MappedIterator(
 559                         $dbr->select( 'job', '*', array( 'job_cmd' => $this->getType(), 'job_token' => '' ) ),
 560                         function( $row ) use ( $scope ) {
 561                                 $job = Job::factory(
 562                                         $row->job_cmd,
 563                                         Title::makeTitle( $row->job_namespace, $row->job_title ),
 564                                         strlen( $row->job_params ) ? unserialize( $row->job_params ) : false,
 565                                         $row->job_id
 566                                 );
 567                                 $job->metadata['id'] = $row->job_id;
 568                                 $job->id = $row->job_id; // XXX: work around broken subclasses
 569                                 return $job;
 570                         }
 571                 );
 572         }
 573
 574         /**
 575          * Recycle or destroy any jobs that have been claimed for too long
 576          *
 577          * @return integer Number of jobs recycled/deleted
 578          */
 579         public function recycleAndDeleteStaleJobs() {
 580                 $now = time();
 581                 list( $dbw, $scope ) = $this->getMasterDB();
 582                 $count = 0; // affected rows
 583
 584                 if ( !$dbw->lock( "jobqueue-recycle-{$this->type}", __METHOD__, 1 ) ) {
 585                         return $count; // already in progress
 586                 }
 587
 588                 // Remove claims on jobs acquired for too long if enabled...
 589                 if ( $this->claimTTL > 0 ) {
 590                         $claimCutoff = $dbw->timestamp( $now - $this->claimTTL );
 591                         // Get the IDs of jobs that have be claimed but not finished after too long.
 592                         // These jobs can be recycled into the queue by expiring the claim. Selecting
 593                         // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
 594                         $res = $dbw->select( 'job', 'job_id',
 595                                 array(
 596                                         'job_cmd' => $this->type,
 597                                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 598                                         "job_token_timestamp < {$dbw->addQuotes( $claimCutoff )}", // stale
 599                                         "job_attempts < {$dbw->addQuotes( $this->maxTries )}" ), // retries left
 600                                 __METHOD__
 601                         );
 602                         $ids = array_map(
 603                                 function( $o ) {
 604                                         return $o->job_id;
 605                                 }, iterator_to_array( $res )
 606                         );
 607                         if ( count( $ids ) ) {
 608                                 // Reset job_token for these jobs so that other runners will pick them up.
 609                                 // Set the timestamp to the current time, as it is useful to now that the job
 610                                 // was already tried before (the timestamp becomes the "released" time).
 611                                 $dbw->update( 'job',
 612                                         array(
 613                                                 'job_token' => '',
 614                                                 'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
 615                                         array(
 616                                                 'job_id' => $ids ),
 617                                         __METHOD__
 618                                 );
 619                                 $count += $dbw->affectedRows();
 620                                 JobQueue::incrStats( 'job-recycle', $this->type, $dbw->affectedRows() );
 621                                 $this->cache->set( $this->getCacheKey( 'empty' ), 'false', self::CACHE_TTL_LONG );
 622                         }
 623                 }
 624
 625                 // Just destroy any stale jobs...
 626                 $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
 627                 $conds = array(
 628                         'job_cmd' => $this->type,
 629                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 630                         "job_token_timestamp < {$dbw->addQuotes( $pruneCutoff )}" // stale
 631                 );
 632                 if ( $this->claimTTL > 0 ) { // only prune jobs attempted too many times...
 633                         $conds[] = "job_attempts >= {$dbw->addQuotes( $this->maxTries )}";
 634                 }
 635                 // Get the IDs of jobs that are considered stale and should be removed. Selecting
 636                 // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
 637                 $res = $dbw->select( 'job', 'job_id', $conds, __METHOD__ );
 638                 $ids = array_map(
 639                         function( $o ) {
 640                                 return $o->job_id;
 641                         }, iterator_to_array( $res )
 642                 );
 643                 if ( count( $ids ) ) {
 644                         $dbw->delete( 'job', array( 'job_id' => $ids ), __METHOD__ );
 645                         $count += $dbw->affectedRows();
 646                         JobQueue::incrStats( 'job-abandon', $this->type, $dbw->affectedRows() );
 647                 }
 648
 649                 $dbw->unlock( "jobqueue-recycle-{$this->type}", __METHOD__ );
 650
 651                 return $count;
 652         }
 653
 654         /**
 655          * @return Array (DatabaseBase, ScopedCallback)
 656          */
 657         protected function getSlaveDB() {
 658                 return $this->getDB( DB_SLAVE );
 659         }
 660
 661         /**
 662          * @return Array (DatabaseBase, ScopedCallback)
 663          */
 664         protected function getMasterDB() {
 665                 return $this->getDB( DB_MASTER );
 666         }
 667
 668         /**
 669          * @param $index integer (DB_SLAVE/DB_MASTER)
 670          * @return Array (DatabaseBase, ScopedCallback)
 671          */
 672         protected function getDB( $index ) {
 673                 $lb = ( $this->cluster !== false )
 674                         ? wfGetLBFactory()->getExternalLB( $this->cluster, $this->wiki )
 675                         : wfGetLB( $this->wiki );
 676                 $conn = $lb->getConnection( $index, array(), $this->wiki );
 677                 return array(
 678                         $conn,
 679                         new ScopedCallback( function() use ( $lb, $conn ) {
 680                                 $lb->reuseConnection( $conn );
 681                         } )
 682                 );
 683         }
 684
 685         /**
 686          * @param $job Job
 687          * @return array
 688          */
 689         protected function insertFields( Job $job ) {
 690                 list( $dbw, $scope ) = $this->getMasterDB();
 691                 return array(
 692                         // Fields that describe the nature of the job
 693                         'job_cmd'       => $job->getType(),
 694                         'job_namespace' => $job->getTitle()->getNamespace(),
 695                         'job_title'     => $job->getTitle()->getDBkey(),
 696                         'job_params'    => self::makeBlob( $job->getParams() ),
 697                         // Additional job metadata
 698                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 699                         'job_timestamp' => $dbw->timestamp(),
 700                         'job_sha1'      => wfBaseConvert(
 701                                 sha1( serialize( $job->getDeduplicationInfo() ) ),
 702                                 16, 36, 31
 703                         ),
 704                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 705                 );
 706         }
 707
 708         /**
 709          * @return string
 710          */
 711         private function getCacheKey( $property ) {
 712                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 713                 $cluster = is_string( $this->cluster ) ? $this->cluster : 'main';
 714                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $cluster, $this->type, $property );
 715         }
 716
 717         /**
 718          * @param $params
 719          * @return string
 720          */
 721         protected static function makeBlob( $params ) {
 722                 if ( $params !== false ) {
 723                         return serialize( $params );
 724                 } else {
 725                         return '';
 726                 }
 727         }
 728
 729         /**
 730          * @param $blob
 731          * @return bool|mixed
 732          */
 733         protected static function extractBlob( $blob ) {
 734                 if ( (string)$blob !== '' ) {
 735                         return unserialize( $blob );
 736                 } else {
 737                         return false;
 738                 }
 739         }
 740 }