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                 if ( count( $jobs ) ) {
 181                         list( $dbw, $scope ) = $this->getMasterDB();
 182
 183                         $rowSet = array(); // (sha1 => job) map for jobs that are de-duplicated
 184                         $rowList = array(); // list of jobs for jobs that are are not de-duplicated
 185
 186                         foreach ( $jobs as $job ) {
 187                                 $row = $this->insertFields( $job );
 188                                 if ( $job->ignoreDuplicates() ) {
 189                                         $rowSet[$row['job_sha1']] = $row;
 190                                 } else {
 191                                         $rowList[] = $row;
 192                                 }
 193                         }
 194
 195                         $key = $this->getCacheKey( 'empty' );
 196                         $atomic = ( $flags & self::QOS_ATOMIC );
 197                         $cache = $this->cache;
 198                         $method = __METHOD__;
 199
 200                         $dbw->onTransactionIdle(
 201                                 function() use ( $dbw, $cache, $rowSet, $rowList, $atomic, $key, $method, $scope
 202                         ) {
 203                                 if ( $atomic ) {
 204                                         $dbw->begin( $method ); // wrap all the job additions in one transaction
 205                                 }
 206                                 try {
 207                                         // Strip out any duplicate jobs that are already in the queue...
 208                                         if ( count( $rowSet ) ) {
 209                                                 $res = $dbw->select( 'job', 'job_sha1',
 210                                                         array(
 211                                                                 // No job_type condition since it's part of the job_sha1 hash
 212                                                                 'job_sha1'  => array_keys( $rowSet ),
 213                                                                 'job_token' => '' // unclaimed
 214                                                         ),
 215                                                         $method
 216                                                 );
 217                                                 foreach ( $res as $row ) {
 218                                                         wfDebug( "Job with hash '{$row->job_sha1}' is a duplicate." );
 219                                                         unset( $rowSet[$row->job_sha1] ); // already enqueued
 220                                                 }
 221                                         }
 222                                         // Build the full list of job rows to insert
 223                                         $rows = array_merge( $rowList, array_values( $rowSet ) );
 224                                         // Insert the job rows in chunks to avoid slave lag...
 225                                         foreach ( array_chunk( $rows, 50 ) as $rowBatch ) {
 226                                                 $dbw->insert( 'job', $rowBatch, $method );
 227                                         }
 228                                         wfIncrStats( 'job-insert', count( $rows ) );
 229                                         wfIncrStats( 'job-insert-duplicate',
 230                                                 count( $rowSet ) + count( $rowList ) - count( $rows ) );
 231                                 } catch ( DBError $e ) {
 232                                         if ( $atomic ) {
 233                                                 $dbw->rollback( $method );
 234                                         }
 235                                         throw $e;
 236                                 }
 237                                 if ( $atomic ) {
 238                                         $dbw->commit( $method );
 239                                 }
 240
 241                                 $cache->set( $key, 'false', JobQueueDB::CACHE_TTL_LONG );
 242                         } );
 243                 }
 244
 245                 return true;
 246         }
 247
 248         /**
 249          * @see JobQueue::doPop()
 250          * @return Job|bool
 251          */
 252         protected function doPop() {
 253                 if ( $this->cache->get( $this->getCacheKey( 'empty' ) ) === 'true' ) {
 254                         return false; // queue is empty
 255                 }
 256
 257                 list( $dbw, $scope ) = $this->getMasterDB();
 258                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 259
 260                 $uuid = wfRandomString( 32 ); // pop attempt
 261                 $job = false; // job popped off
 262                 do { // retry when our row is invalid or deleted as a duplicate
 263                         // Try to reserve a row in the DB...
 264                         if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
 265                                 $row = $this->claimOldest( $uuid );
 266                         } else { // random first
 267                                 $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 268                                 $gte = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 269                                 $row = $this->claimRandom( $uuid, $rand, $gte );
 270                         }
 271                         // Check if we found a row to reserve...
 272                         if ( !$row ) {
 273                                 $this->cache->set( $this->getCacheKey( 'empty' ), 'true', self::CACHE_TTL_LONG );
 274                                 break; // nothing to do
 275                         }
 276                         wfIncrStats( 'job-pop' );
 277                         // Get the job object from the row...
 278                         $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 279                         if ( !$title ) {
 280                                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 281                                 wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
 282                                 continue; // try again
 283                         }
 284                         $job = Job::factory( $row->job_cmd, $title,
 285                                 self::extractBlob( $row->job_params ), $row->job_id );
 286                         $job->id = $row->job_id; // XXX: work around broken subclasses
 287                         break; // done
 288                 } while( true );
 289
 290                 return $job;
 291         }
 292
 293         /**
 294          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 295          *
 296          * @param string $uuid 32 char hex string
 297          * @param $rand integer Random unsigned integer (31 bits)
 298          * @param bool $gte Search for job_random >= $random (otherwise job_random <= $random)
 299          * @return Row|false
 300          */
 301         protected function claimRandom( $uuid, $rand, $gte ) {
 302                 list( $dbw, $scope ) = $this->getMasterDB();
 303                 // Check cache to see if the queue has <= OFFSET items
 304                 $tinyQueue = $this->cache->get( $this->getCacheKey( 'small' ) );
 305
 306                 $row = false; // the row acquired
 307                 $invertedDirection = false; // whether one job_random direction was already scanned
 308                 // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
 309                 // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
 310                 // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
 311                 // be used here with MySQL.
 312                 do {
 313                         if ( $tinyQueue ) { // queue has <= MAX_OFFSET rows
 314                                 // For small queues, using OFFSET will overshoot and return no rows more often.
 315                                 // Instead, this uses job_random to pick a row (possibly checking both directions).
 316                                 $ineq = $gte ? '>=' : '<=';
 317                                 $dir = $gte ? 'ASC' : 'DESC';
 318                                 $row = $dbw->selectRow( 'job', '*', // find a random job
 319                                         array(
 320                                                 'job_cmd'   => $this->type,
 321                                                 'job_token' => '', // unclaimed
 322                                                 "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 323                                         __METHOD__,
 324                                         array( 'ORDER BY' => "job_random {$dir}" )
 325                                 );
 326                                 if ( !$row && !$invertedDirection ) {
 327                                         $gte = !$gte;
 328                                         $invertedDirection = true;
 329                                         continue; // try the other direction
 330                                 }
 331                         } else { // table *may* have >= MAX_OFFSET rows
 332                                 // Bug 42614: "ORDER BY job_random" with a job_random inequality causes high CPU
 333                                 // in MySQL if there are many rows for some reason. This uses a small OFFSET
 334                                 // instead of job_random for reducing excess claim retries.
 335                                 $row = $dbw->selectRow( 'job', '*', // find a random job
 336                                         array(
 337                                                 'job_cmd'   => $this->type,
 338                                                 'job_token' => '', // unclaimed
 339                                         ),
 340                                         __METHOD__,
 341                                         array( 'OFFSET' => mt_rand( 0, self::MAX_OFFSET ) )
 342                                 );
 343                                 if ( !$row ) {
 344                                         $tinyQueue = true; // we know the queue must have <= MAX_OFFSET rows
 345                                         $this->cache->set( $this->getCacheKey( 'small' ), 1, 30 );
 346                                         continue; // use job_random
 347                                 }
 348                         }
 349                         if ( $row ) { // claim the job
 350                                 $dbw->update( 'job', // update by PK
 351                                         array(
 352                                                 'job_token'           => $uuid,
 353                                                 'job_token_timestamp' => $dbw->timestamp(),
 354                                                 'job_attempts = job_attempts+1' ),
 355                                         array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
 356                                         __METHOD__
 357                                 );
 358                                 // This might get raced out by another runner when claiming the previously
 359                                 // selected row. The use of job_random should minimize this problem, however.
 360                                 if ( !$dbw->affectedRows() ) {
 361                                         $row = false; // raced out
 362                                 }
 363                         } else {
 364                                 break; // nothing to do
 365                         }
 366                 } while ( !$row );
 367
 368                 return $row;
 369         }
 370
 371         /**
 372          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 373          *
 374          * @param string $uuid 32 char hex string
 375          * @return Row|false
 376          */
 377         protected function claimOldest( $uuid ) {
 378                 list( $dbw, $scope ) = $this->getMasterDB();
 379
 380                 $row = false; // the row acquired
 381                 do {
 382                         if ( $dbw->getType() === 'mysql' ) {
 383                                 // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 384                                 // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 385                                 // Oracle and Postgre have no such limitation. However, MySQL offers an
 386                                 // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 387                                 $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
 388                                         "SET " .
 389                                                 "job_token = {$dbw->addQuotes( $uuid ) }, " .
 390                                                 "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
 391                                                 "job_attempts = job_attempts+1 " .
 392                                         "WHERE ( " .
 393                                                 "job_cmd = {$dbw->addQuotes( $this->type )} " .
 394                                                 "AND job_token = {$dbw->addQuotes( '' )} " .
 395                                         ") ORDER BY job_id ASC LIMIT 1",
 396                                         __METHOD__
 397                                 );
 398                         } else {
 399                                 // Use a subquery to find the job, within an UPDATE to claim it.
 400                                 // This uses as much of the DB wrapper functions as possible.
 401                                 $dbw->update( 'job',
 402                                         array(
 403                                                 'job_token'           => $uuid,
 404                                                 'job_token_timestamp' => $dbw->timestamp(),
 405                                                 'job_attempts = job_attempts+1' ),
 406                                         array( 'job_id = (' .
 407                                                 $dbw->selectSQLText( 'job', 'job_id',
 408                                                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
 409                                                         __METHOD__,
 410                                                         array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
 411                                                 ')'
 412                                         ),
 413                                         __METHOD__
 414                                 );
 415                         }
 416                         // Fetch any row that we just reserved...
 417                         if ( $dbw->affectedRows() ) {
 418                                 $row = $dbw->selectRow( 'job', '*',
 419                                         array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
 420                                 );
 421                                 if ( !$row ) { // raced out by duplicate job removal
 422                                         wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
 423                                 }
 424                         } else {
 425                                 break; // nothing to do
 426                         }
 427                 } while ( !$row );
 428
 429                 return $row;
 430         }
 431
 432         /**
 433          * @see JobQueue::doAck()
 434          * @param Job $job
 435          * @throws MWException
 436          * @return Job|bool
 437          */
 438         protected function doAck( Job $job ) {
 439                 if ( !$job->getId() ) {
 440                         throw new MWException( "Job of type '{$job->getType()}' has no ID." );
 441                 }
 442
 443                 list( $dbw, $scope ) = $this->getMasterDB();
 444                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 445
 446                 // Delete a row with a single DELETE without holding row locks over RTTs...
 447                 $dbw->delete( 'job',
 448                         array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ), __METHOD__ );
 449
 450                 return true;
 451         }
 452
 453         /**
 454          * @see JobQueue::doDeduplicateRootJob()
 455          * @param Job $job
 456          * @throws MWException
 457          * @return bool
 458          */
 459         protected function doDeduplicateRootJob( Job $job ) {
 460                 $params = $job->getParams();
 461                 if ( !isset( $params['rootJobSignature'] ) ) {
 462                         throw new MWException( "Cannot register root job; missing 'rootJobSignature'." );
 463                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 464                         throw new MWException( "Cannot register root job; missing 'rootJobTimestamp'." );
 465                 }
 466                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 467                 // Callers should call batchInsert() and then this function so that if the insert
 468                 // fails, the de-duplication registration will be aborted. Since the insert is
 469                 // deferred till "transaction idle", do the same here, so that the ordering is
 470                 // maintained. Having only the de-duplication registration succeed would cause
 471                 // jobs to become no-ops without any actual jobs that made them redundant.
 472                 list( $dbw, $scope ) = $this->getMasterDB();
 473                 $cache = $this->cache;
 474                 $dbw->onTransactionIdle( function() use ( $cache, $params, $key, $scope ) {
 475                         $timestamp = $cache->get( $key ); // current last timestamp of this job
 476                         if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 477                                 return true; // a newer version of this root job was enqueued
 478                         }
 479
 480                         // Update the timestamp of the last root job started at the location...
 481                         return $cache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 482                 } );
 483
 484                 return true;
 485         }
 486
 487         /**
 488          * @see JobQueue::doWaitForBackups()
 489          * @return void
 490          */
 491         protected function doWaitForBackups() {
 492                 wfWaitForSlaves();
 493         }
 494
 495         /**
 496          * @return Array
 497          */
 498         protected function doGetPeriodicTasks() {
 499                 return array(
 500                         'recycleAndDeleteStaleJobs' => array(
 501                                 'callback' => array( $this, 'recycleAndDeleteStaleJobs' ),
 502                                 'period'   => ceil( $this->claimTTL / 2 )
 503                         )
 504                 );
 505         }
 506
 507         /**
 508          * @return void
 509          */
 510         protected function doFlushCaches() {
 511                 foreach ( array( 'empty', 'size', 'acquiredcount' ) as $type ) {
 512                         $this->cache->delete( $this->getCacheKey( $type ) );
 513                 }
 514         }
 515
 516         /**
 517          * @see JobQueue::getAllQueuedJobs()
 518          * @return Iterator
 519          */
 520         public function getAllQueuedJobs() {
 521                 list( $dbr, $scope ) = $this->getSlaveDB();
 522                 return new MappedIterator(
 523                         $dbr->select( 'job', '*', array( 'job_cmd' => $this->getType(), 'job_token' => '' ) ),
 524                         function( $row ) use ( $scope ) {
 525                                 $job = Job::factory(
 526                                         $row->job_cmd,
 527                                         Title::makeTitle( $row->job_namespace, $row->job_title ),
 528                                         strlen( $row->job_params ) ? unserialize( $row->job_params ) : false,
 529                                         $row->job_id
 530                                 );
 531                                 $job->id = $row->job_id; // XXX: work around broken subclasses
 532                                 return $job;
 533                         }
 534                 );
 535         }
 536
 537         /**
 538          * Recycle or destroy any jobs that have been claimed for too long
 539          *
 540          * @return integer Number of jobs recycled/deleted
 541          */
 542         public function recycleAndDeleteStaleJobs() {
 543                 $now = time();
 544                 list( $dbw, $scope ) = $this->getMasterDB();
 545                 $count = 0; // affected rows
 546
 547                 if ( !$dbw->lock( "jobqueue-recycle-{$this->type}", __METHOD__, 1 ) ) {
 548                         return $count; // already in progress
 549                 }
 550
 551                 // Remove claims on jobs acquired for too long if enabled...
 552                 if ( $this->claimTTL > 0 ) {
 553                         $claimCutoff = $dbw->timestamp( $now - $this->claimTTL );
 554                         // Get the IDs of jobs that have be claimed but not finished after too long.
 555                         // These jobs can be recycled into the queue by expiring the claim. Selecting
 556                         // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
 557                         $res = $dbw->select( 'job', 'job_id',
 558                                 array(
 559                                         'job_cmd' => $this->type,
 560                                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 561                                         "job_token_timestamp < {$dbw->addQuotes( $claimCutoff )}", // stale
 562                                         "job_attempts < {$dbw->addQuotes( $this->maxTries )}" ), // retries left
 563                                 __METHOD__
 564                         );
 565                         $ids = array_map( function( $o ) { return $o->job_id; }, iterator_to_array( $res ) );
 566                         if ( count( $ids ) ) {
 567                                 // Reset job_token for these jobs so that other runners will pick them up.
 568                                 // Set the timestamp to the current time, as it is useful to now that the job
 569                                 // was already tried before (the timestamp becomes the "released" time).
 570                                 $dbw->update( 'job',
 571                                         array(
 572                                                 'job_token' => '',
 573                                                 'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
 574                                         array(
 575                                                 'job_id' => $ids ),
 576                                         __METHOD__
 577                                 );
 578                                 $count += $dbw->affectedRows();
 579                                 wfIncrStats( 'job-recycle', $dbw->affectedRows() );
 580                                 $this->cache->set( $this->getCacheKey( 'empty' ), 'false', self::CACHE_TTL_LONG );
 581                         }
 582                 }
 583
 584                 // Just destroy any stale jobs...
 585                 $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
 586                 $conds = array(
 587                         'job_cmd' => $this->type,
 588                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 589                         "job_token_timestamp < {$dbw->addQuotes( $pruneCutoff )}" // stale
 590                 );
 591                 if ( $this->claimTTL > 0 ) { // only prune jobs attempted too many times...
 592                         $conds[] = "job_attempts >= {$dbw->addQuotes( $this->maxTries )}";
 593                 }
 594                 // Get the IDs of jobs that are considered stale and should be removed. Selecting
 595                 // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
 596                 $res = $dbw->select( 'job', 'job_id', $conds, __METHOD__ );
 597                 $ids = array_map( function( $o ) { return $o->job_id; }, iterator_to_array( $res ) );
 598                 if ( count( $ids ) ) {
 599                         $dbw->delete( 'job', array( 'job_id' => $ids ), __METHOD__ );
 600                         $count += $dbw->affectedRows();
 601                 }
 602
 603                 $dbw->unlock( "jobqueue-recycle-{$this->type}", __METHOD__ );
 604
 605                 return $count;
 606         }
 607
 608         /**
 609          * @return Array (DatabaseBase, ScopedCallback)
 610          */
 611         protected function getSlaveDB() {
 612                 return $this->getDB( DB_SLAVE );
 613         }
 614
 615         /**
 616          * @return Array (DatabaseBase, ScopedCallback)
 617          */
 618         protected function getMasterDB() {
 619                 return $this->getDB( DB_MASTER );
 620         }
 621
 622         /**
 623          * @param $index integer (DB_SLAVE/DB_MASTER)
 624          * @return Array (DatabaseBase, ScopedCallback)
 625          */
 626         protected function getDB( $index ) {
 627                 $lb = ( $this->cluster !== false )
 628                         ? wfGetLBFactory()->getExternalLB( $this->cluster, $this->wiki )
 629                         : wfGetLB( $this->wiki );
 630                 $conn = $lb->getConnection( $index, array(), $this->wiki );
 631                 return array(
 632                         $conn,
 633                         new ScopedCallback( function() use ( $lb, $conn ) {
 634                                 $lb->reuseConnection( $conn );
 635                         } )
 636                 );
 637         }
 638
 639         /**
 640          * @param $job Job
 641          * @return array
 642          */
 643         protected function insertFields( Job $job ) {
 644                 list( $dbw, $scope ) = $this->getMasterDB();
 645                 return array(
 646                         // Fields that describe the nature of the job
 647                         'job_cmd'       => $job->getType(),
 648                         'job_namespace' => $job->getTitle()->getNamespace(),
 649                         'job_title'     => $job->getTitle()->getDBkey(),
 650                         'job_params'    => self::makeBlob( $job->getParams() ),
 651                         // Additional job metadata
 652                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 653                         'job_timestamp' => $dbw->timestamp(),
 654                         'job_sha1'      => wfBaseConvert(
 655                                 sha1( serialize( $job->getDeduplicationInfo() ) ),
 656                                 16, 36, 31
 657                         ),
 658                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 659                 );
 660         }
 661
 662         /**
 663          * @return string
 664          */
 665         private function getCacheKey( $property ) {
 666                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 667                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, $property );
 668         }
 669
 670         /**
 671          * @param $params
 672          * @return string
 673          */
 674         protected static function makeBlob( $params ) {
 675                 if ( $params !== false ) {
 676                         return serialize( $params );
 677                 } else {
 678                         return '';
 679                 }
 680         }
 681
 682         /**
 683          * @param $blob
 684          * @return bool|mixed
 685          */
 686         protected static function extractBlob( $blob ) {
 687                 if ( (string)$blob !== '' ) {
 688                         return unserialize( $blob );
 689                 } else {
 690                         return false;
 691                 }
 692         }
 693 }