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