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