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 ROOTJOB_TTL     = 1209600; // integer; seconds to remember root jobs (14 days)
  32         const CACHE_TTL_SHORT = 30; // integer; seconds to cache info without re-validating
  33         const CACHE_TTL_LONG  = 300; // integer; seconds to cache info that is kept up to date
  34         const MAX_AGE_PRUNE   = 604800; // integer; seconds a job can live once claimed
  35         const MAX_JOB_RANDOM  = 2147483647; // integer; 2^31 - 1, used for job_random
  36         const MAX_OFFSET      = 255; // integer; maximum number of rows to skip
  37
  38         protected $cluster = false; // string; name of an external DB cluster
  39
  40         /**
  41          * Additional parameters include:
  42          *   - cluster : The name of an external cluster registered via LBFactory.
  43          *               If not specified, the primary DB cluster for the wiki will be used.
  44          *               This can be overridden with a custom cluster so that DB handles will
  45          *               be retrieved via LBFactory::getExternalLB() and getConnection().
  46          * @param $params array
  47          */
  48         protected function __construct( array $params ) {
  49                 parent::__construct( $params );
  50                 $this->cluster = isset( $params['cluster'] ) ? $params['cluster'] : false;
  51         }
  52
  53         /**
  54          * @see JobQueue::doIsEmpty()
  55          * @return bool
  56          */
  57         protected function doIsEmpty() {
  58                 global $wgMemc;
  59
  60                 $key = $this->getCacheKey( 'empty' );
  61
  62                 $isEmpty = $wgMemc->get( $key );
  63                 if ( $isEmpty === 'true' ) {
  64                         return true;
  65                 } elseif ( $isEmpty === 'false' ) {
  66                         return false;
  67                 }
  68
  69                 list( $dbr, $scope ) = $this->getSlaveDB();
  70                 $found = $dbr->selectField( // unclaimed job
  71                         'job', '1', array( 'job_cmd' => $this->type, 'job_token' => '' ), __METHOD__
  72                 );
  73                 $wgMemc->add( $key, $found ? 'false' : 'true', self::CACHE_TTL_LONG );
  74
  75                 return !$found;
  76         }
  77
  78         /**
  79          * @see JobQueue::doGetSize()
  80          * @return integer
  81          */
  82         protected function doGetSize() {
  83                 global $wgMemc;
  84
  85                 $key = $this->getCacheKey( 'size' );
  86
  87                 $size = $wgMemc->get( $key );
  88                 if ( is_int( $size ) ) {
  89                         return $size;
  90                 }
  91
  92                 list( $dbr, $scope ) = $this->getSlaveDB();
  93                 $size = (int)$dbr->selectField( 'job', 'COUNT(*)',
  94                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
  95                         __METHOD__
  96                 );
  97                 $wgMemc->set( $key, $size, self::CACHE_TTL_SHORT );
  98
  99                 return $size;
 100         }
 101
 102         /**
 103          * @see JobQueue::doGetAcquiredCount()
 104          * @return integer
 105          */
 106         protected function doGetAcquiredCount() {
 107                 global $wgMemc;
 108
 109                 $key = $this->getCacheKey( 'acquiredcount' );
 110
 111                 $count = $wgMemc->get( $key );
 112                 if ( is_int( $count ) ) {
 113                         return $count;
 114                 }
 115
 116                 list( $dbr, $scope ) = $this->getSlaveDB();
 117                 $count = (int)$dbr->selectField( 'job', 'COUNT(*)',
 118                         array( 'job_cmd' => $this->type, "job_token != {$dbr->addQuotes( '' )}" ),
 119                         __METHOD__
 120                 );
 121                 $wgMemc->set( $key, $count, self::CACHE_TTL_SHORT );
 122
 123                 return $count;
 124         }
 125
 126         /**
 127          * @see JobQueue::doBatchPush()
 128          * @param array $jobs
 129          * @param $flags
 130          * @throws DBError|Exception
 131          * @return bool
 132          */
 133         protected function doBatchPush( array $jobs, $flags ) {
 134                 if ( count( $jobs ) ) {
 135                         list( $dbw, $scope ) = $this->getMasterDB();
 136
 137                         $rowSet = array(); // (sha1 => job) map for jobs that are de-duplicated
 138                         $rowList = array(); // list of jobs for jobs that are are not de-duplicated
 139
 140                         foreach ( $jobs as $job ) {
 141                                 $row = $this->insertFields( $job );
 142                                 if ( $job->ignoreDuplicates() ) {
 143                                         $rowSet[$row['job_sha1']] = $row;
 144                                 } else {
 145                                         $rowList[] = $row;
 146                                 }
 147                         }
 148
 149                         $atomic = ( $flags & self::QoS_Atomic );
 150                         $key    = $this->getCacheKey( 'empty' );
 151                         $ttl    = self::CACHE_TTL_LONG;
 152
 153                         $dbw->onTransactionIdle(
 154                                 function() use ( $dbw, $rowSet, $rowList, $atomic, $key, $ttl, $scope
 155                         ) {
 156                                 global $wgMemc;
 157
 158                                 if ( $atomic ) {
 159                                         $dbw->begin( __METHOD__ ); // wrap all the job additions in one transaction
 160                                 }
 161                                 try {
 162                                         // Strip out any duplicate jobs that are already in the queue...
 163                                         if ( count( $rowSet ) ) {
 164                                                 $res = $dbw->select( 'job', 'job_sha1',
 165                                                         array(
 166                                                                 // No job_type condition since it's part of the job_sha1 hash
 167                                                                 'job_sha1'  => array_keys( $rowSet ),
 168                                                                 'job_token' => '' // unclaimed
 169                                                         ),
 170                                                         __METHOD__
 171                                                 );
 172                                                 foreach ( $res as $row ) {
 173                                                         wfDebug( "Job with hash '{$row->job_sha1}' is a duplicate." );
 174                                                         unset( $rowSet[$row->job_sha1] ); // already enqueued
 175                                                 }
 176                                         }
 177                                         // Build the full list of job rows to insert
 178                                         $rows = array_merge( $rowList, array_values( $rowSet ) );
 179                                         // Insert the job rows in chunks to avoid slave lag...
 180                                         foreach ( array_chunk( $rows, 50 ) as $rowBatch ) {
 181                                                 $dbw->insert( 'job', $rowBatch, __METHOD__ );
 182                                         }
 183                                         wfIncrStats( 'job-insert', count( $rows ) );
 184                                         wfIncrStats( 'job-insert-duplicate',
 185                                                 count( $rowSet ) + count( $rowList ) - count( $rows ) );
 186                                 } catch ( DBError $e ) {
 187                                         if ( $atomic ) {
 188                                                 $dbw->rollback( __METHOD__ );
 189                                         }
 190                                         throw $e;
 191                                 }
 192                                 if ( $atomic ) {
 193                                         $dbw->commit( __METHOD__ );
 194                                 }
 195
 196                                 $wgMemc->set( $key, 'false', $ttl ); // queue is not empty
 197                         } );
 198                 }
 199
 200                 return true;
 201         }
 202
 203         /**
 204          * @see JobQueue::doPop()
 205          * @return Job|bool
 206          */
 207         protected function doPop() {
 208                 global $wgMemc;
 209
 210                 if ( $wgMemc->get( $this->getCacheKey( 'empty' ) ) === 'true' ) {
 211                         return false; // queue is empty
 212                 }
 213
 214                 list( $dbw, $scope ) = $this->getMasterDB();
 215                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 216
 217                 $uuid = wfRandomString( 32 ); // pop attempt
 218                 $job = false; // job popped off
 219                 do { // retry when our row is invalid or deleted as a duplicate
 220                         // Try to reserve a row in the DB...
 221                         if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
 222                                 $row = $this->claimOldest( $uuid );
 223                         } else { // random first
 224                                 $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 225                                 $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 226                                 $row  = $this->claimRandom( $uuid, $rand, $gte );
 227                         }
 228                         // Check if we found a row to reserve...
 229                         if ( !$row ) {
 230                                 $wgMemc->set( $this->getCacheKey( 'empty' ), 'true', self::CACHE_TTL_LONG );
 231                                 break; // nothing to do
 232                         }
 233                         wfIncrStats( 'job-pop' );
 234                         // Get the job object from the row...
 235                         $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 236                         if ( !$title ) {
 237                                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 238                                 wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
 239                                 continue; // try again
 240                         }
 241                         $job = Job::factory( $row->job_cmd, $title,
 242                                 self::extractBlob( $row->job_params ), $row->job_id );
 243                         $job->id = $row->job_id; // XXX: work around broken subclasses
 244                         // Flag this job as an old duplicate based on its "root" job...
 245                         if ( $this->isRootJobOldDuplicate( $job ) ) {
 246                                 wfIncrStats( 'job-pop-duplicate' );
 247                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 248                         }
 249                         break; // done
 250                 } while( true );
 251
 252                 return $job;
 253         }
 254
 255         /**
 256          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 257          *
 258          * @param $uuid string 32 char hex string
 259          * @param $rand integer Random unsigned integer (31 bits)
 260          * @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
 261          * @return Row|false
 262          */
 263         protected function claimRandom( $uuid, $rand, $gte ) {
 264                 global $wgMemc;
 265
 266                 list( $dbw, $scope ) = $this->getMasterDB();
 267                 // Check cache to see if the queue has <= OFFSET items
 268                 $tinyQueue = $wgMemc->get( $this->getCacheKey( 'small' ) );
 269
 270                 $row = false; // the row acquired
 271                 $invertedDirection = false; // whether one job_random direction was already scanned
 272                 // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
 273                 // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
 274                 // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
 275                 // be used here with MySQL.
 276                 do {
 277                         if ( $tinyQueue ) { // queue has <= MAX_OFFSET rows
 278                                 // For small queues, using OFFSET will overshoot and return no rows more often.
 279                                 // Instead, this uses job_random to pick a row (possibly checking both directions).
 280                                 $ineq = $gte ? '>=' : '<=';
 281                                 $dir  = $gte ? 'ASC' : 'DESC';
 282                                 $row  = $dbw->selectRow( 'job', '*', // find a random job
 283                                         array(
 284                                                 'job_cmd'   => $this->type,
 285                                                 'job_token' => '', // unclaimed
 286                                                 "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 287                                         __METHOD__,
 288                                         array( 'ORDER BY' => "job_random {$dir}" )
 289                                 );
 290                                 if ( !$row && !$invertedDirection ) {
 291                                         $gte = !$gte;
 292                                         $invertedDirection = true;
 293                                         continue; // try the other direction
 294                                 }
 295                         } else { // table *may* have >= MAX_OFFSET rows
 296                                 // Bug 42614: "ORDER BY job_random" with a job_random inequality causes high CPU
 297                                 // in MySQL if there are many rows for some reason. This uses a small OFFSET
 298                                 // instead of job_random for reducing excess claim retries.
 299                                 $row = $dbw->selectRow( 'job', '*', // find a random job
 300                                         array(
 301                                                 'job_cmd'   => $this->type,
 302                                                 'job_token' => '', // unclaimed
 303                                         ),
 304                                         __METHOD__,
 305                                         array( 'OFFSET' => mt_rand( 0, self::MAX_OFFSET ) )
 306                                 );
 307                                 if ( !$row ) {
 308                                         $tinyQueue = true; // we know the queue must have <= MAX_OFFSET rows
 309                                         $wgMemc->set( $this->getCacheKey( 'small' ), 1, 30 );
 310                                         continue; // use job_random
 311                                 }
 312                         }
 313                         if ( $row ) { // claim the job
 314                                 $dbw->update( 'job', // update by PK
 315                                         array(
 316                                                 'job_token'           => $uuid,
 317                                                 'job_token_timestamp' => $dbw->timestamp(),
 318                                                 'job_attempts = job_attempts+1' ),
 319                                         array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
 320                                         __METHOD__
 321                                 );
 322                                 // This might get raced out by another runner when claiming the previously
 323                                 // selected row. The use of job_random should minimize this problem, however.
 324                                 if ( !$dbw->affectedRows() ) {
 325                                         $row = false; // raced out
 326                                 }
 327                         } else {
 328                                 break; // nothing to do
 329                         }
 330                 } while ( !$row );
 331
 332                 return $row;
 333         }
 334
 335         /**
 336          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 337          *
 338          * @param $uuid string 32 char hex string
 339          * @return Row|false
 340          */
 341         protected function claimOldest( $uuid ) {
 342                 list( $dbw, $scope ) = $this->getMasterDB();
 343
 344                 $row = false; // the row acquired
 345                 do {
 346                         if ( $dbw->getType() === 'mysql' ) {
 347                                 // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 348                                 // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 349                                 // Oracle and Postgre have no such limitation. However, MySQL offers an
 350                                 // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 351                                 $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
 352                                         "SET " .
 353                                                 "job_token = {$dbw->addQuotes( $uuid ) }, " .
 354                                                 "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
 355                                                 "job_attempts = job_attempts+1 " .
 356                                         "WHERE ( " .
 357                                                 "job_cmd = {$dbw->addQuotes( $this->type )} " .
 358                                                 "AND job_token = {$dbw->addQuotes( '' )} " .
 359                                         ") ORDER BY job_id ASC LIMIT 1",
 360                                         __METHOD__
 361                                 );
 362                         } else {
 363                                 // Use a subquery to find the job, within an UPDATE to claim it.
 364                                 // This uses as much of the DB wrapper functions as possible.
 365                                 $dbw->update( 'job',
 366                                         array(
 367                                                 'job_token'           => $uuid,
 368                                                 'job_token_timestamp' => $dbw->timestamp(),
 369                                                 'job_attempts = job_attempts+1' ),
 370                                         array( 'job_id = (' .
 371                                                 $dbw->selectSQLText( 'job', 'job_id',
 372                                                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
 373                                                         __METHOD__,
 374                                                         array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
 375                                                 ')'
 376                                         ),
 377                                         __METHOD__
 378                                 );
 379                         }
 380                         // Fetch any row that we just reserved...
 381                         if ( $dbw->affectedRows() ) {
 382                                 $row = $dbw->selectRow( 'job', '*',
 383                                         array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
 384                                 );
 385                                 if ( !$row ) { // raced out by duplicate job removal
 386                                         wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
 387                                 }
 388                         } else {
 389                                 break; // nothing to do
 390                         }
 391                 } while ( !$row );
 392
 393                 return $row;
 394         }
 395
 396         /**
 397          * Recycle or destroy any jobs that have been claimed for too long
 398          *
 399          * @return integer Number of jobs recycled/deleted
 400          */
 401         public function recycleAndDeleteStaleJobs() {
 402                 global $wgMemc;
 403
 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( self::MAX_ATTEMPTS )}" ), // 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                                 $wgMemc->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( self::MAX_ATTEMPTS )}";
 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                 $dbw->onTransactionIdle( function() use ( $params, $key, $scope ) {
 511                         global $wgMemc;
 512
 513                         $timestamp = $wgMemc->get( $key ); // current last timestamp of this job
 514                         if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 515                                 return true; // a newer version of this root job was enqueued
 516                         }
 517
 518                         // Update the timestamp of the last root job started at the location...
 519                         return $wgMemc->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 520                 } );
 521
 522                 return true;
 523         }
 524
 525         /**
 526          * Check if the "root" job of a given job has been superseded by a newer one
 527          *
 528          * @param $job Job
 529          * @return bool
 530          */
 531         protected function isRootJobOldDuplicate( Job $job ) {
 532                 global $wgMemc;
 533
 534                 $params = $job->getParams();
 535                 if ( !isset( $params['rootJobSignature'] ) ) {
 536                         return false; // job has no de-deplication info
 537                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 538                         trigger_error( "Cannot check root job; missing 'rootJobTimestamp'." );
 539                         return false;
 540                 }
 541
 542                 // Get the last time this root job was enqueued
 543                 $timestamp = $wgMemc->get( $this->getRootJobCacheKey( $params['rootJobSignature'] ) );
 544
 545                 // Check if a new root job was started at the location after this one's...
 546                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 547         }
 548
 549         /**
 550          * @see JobQueue::doWaitForBackups()
 551          * @return void
 552          */
 553         protected function doWaitForBackups() {
 554                 wfWaitForSlaves();
 555         }
 556
 557         /**
 558          * @return Array
 559          */
 560         protected function doGetPeriodicTasks() {
 561                 return array(
 562                         'recycleAndDeleteStaleJobs' => array(
 563                                 'callback' => array( $this, 'recycleAndDeleteStaleJobs' ),
 564                                 'period'   => ceil( $this->claimTTL / 2 )
 565                         )
 566                 );
 567         }
 568
 569         /**
 570          * @return Array (DatabaseBase, ScopedCallback)
 571          */
 572         protected function getSlaveDB() {
 573                 return $this->getDB( DB_SLAVE );
 574         }
 575
 576         /**
 577          * @return Array (DatabaseBase, ScopedCallback)
 578          */
 579         protected function getMasterDB() {
 580                 return $this->getDB( DB_MASTER );
 581         }
 582
 583         /**
 584          * @param $index integer (DB_SLAVE/DB_MASTER)
 585          * @return Array (DatabaseBase, ScopedCallback)
 586          */
 587         protected function getDB( $index ) {
 588                 $lb = ( $this->cluster !== false )
 589                         ? wfGetLBFactory()->getExternalLB( $this->cluster, $this->wiki )
 590                         : wfGetLB( $this->wiki );
 591                 $conn = $lb->getConnection( $index, array(), $this->wiki );
 592                 return array(
 593                         $conn,
 594                         new ScopedCallback( function() use ( $lb, $conn ) {
 595                                 $lb->reuseConnection( $conn );
 596                         } )
 597                 );
 598         }
 599
 600         /**
 601          * @param $job Job
 602          * @return array
 603          */
 604         protected function insertFields( Job $job ) {
 605                 list( $dbw, $scope ) = $this->getMasterDB();
 606                 return array(
 607                         // Fields that describe the nature of the job
 608                         'job_cmd'       => $job->getType(),
 609                         'job_namespace' => $job->getTitle()->getNamespace(),
 610                         'job_title'     => $job->getTitle()->getDBkey(),
 611                         'job_params'    => self::makeBlob( $job->getParams() ),
 612                         // Additional job metadata
 613                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 614                         'job_timestamp' => $dbw->timestamp(),
 615                         'job_sha1'      => wfBaseConvert(
 616                                 sha1( serialize( $job->getDeduplicationInfo() ) ),
 617                                 16, 36, 31
 618                         ),
 619                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 620                 );
 621         }
 622
 623         /**
 624          * @return string
 625          */
 626         private function getCacheKey( $property ) {
 627                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 628                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, $property );
 629         }
 630
 631         /**
 632          * @param string $signature Hash identifier of the root job
 633          * @return string
 634          */
 635         private function getRootJobCacheKey( $signature ) {
 636                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 637                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 638         }
 639
 640         /**
 641          * @param $params
 642          * @return string
 643          */
 644         protected static function makeBlob( $params ) {
 645                 if ( $params !== false ) {
 646                         return serialize( $params );
 647                 } else {
 648                         return '';
 649                 }
 650         }
 651
 652         /**
 653          * @param $blob
 654          * @return bool|mixed
 655          */
 656         protected static function extractBlob( $blob ) {
 657                 if ( (string)$blob !== '' ) {
 658                         return unserialize( $blob );
 659                 } else {
 660                         return false;
 661                 }
 662         }
 663 }