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