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                 if ( $this->claimTTL <= 0 ) {
 110                         return 0; // no acknowledgements
 111                 }
 112
 113                 $key = $this->getCacheKey( 'acquiredcount' );
 114
 115                 $count = $wgMemc->get( $key );
 116                 if ( is_int( $count ) ) {
 117                         return $count;
 118                 }
 119
 120                 list( $dbr, $scope ) = $this->getSlaveDB();
 121                 $count = (int)$dbr->selectField( 'job', 'COUNT(*)',
 122                         array( 'job_cmd' => $this->type, "job_token != {$dbr->addQuotes( '' )}" ),
 123                         __METHOD__
 124                 );
 125                 $wgMemc->set( $key, $count, self::CACHE_TTL_SHORT );
 126
 127                 return $count;
 128         }
 129
 130         /**
 131          * @see JobQueue::doBatchPush()
 132          * @param array $jobs
 133          * @param $flags
 134          * @throws DBError|Exception
 135          * @return bool
 136          */
 137         protected function doBatchPush( array $jobs, $flags ) {
 138                 if ( count( $jobs ) ) {
 139                         list( $dbw, $scope ) = $this->getMasterDB();
 140
 141                         $rowSet = array(); // (sha1 => job) map for jobs that are de-duplicated
 142                         $rowList = array(); // list of jobs for jobs that are are not de-duplicated
 143
 144                         foreach ( $jobs as $job ) {
 145                                 $row = $this->insertFields( $job );
 146                                 if ( $job->ignoreDuplicates() ) {
 147                                         $rowSet[$row['job_sha1']] = $row;
 148                                 } else {
 149                                         $rowList[] = $row;
 150                                 }
 151                         }
 152
 153                         $atomic = ( $flags & self::QoS_Atomic );
 154                         $key    = $this->getCacheKey( 'empty' );
 155                         $ttl    = self::CACHE_TTL_LONG;
 156
 157                         $dbw->onTransactionIdle(
 158                                 function() use ( $dbw, $rowSet, $rowList, $atomic, $key, $ttl, $scope
 159                         ) {
 160                                 global $wgMemc;
 161
 162                                 if ( $atomic ) {
 163                                         $dbw->begin( __METHOD__ ); // wrap all the job additions in one transaction
 164                                 }
 165                                 try {
 166                                         // Strip out any duplicate jobs that are already in the queue...
 167                                         if ( count( $rowSet ) ) {
 168                                                 $res = $dbw->select( 'job', 'job_sha1',
 169                                                         array(
 170                                                                 // No job_type condition since it's part of the job_sha1 hash
 171                                                                 'job_sha1'  => array_keys( $rowSet ),
 172                                                                 'job_token' => '' // unclaimed
 173                                                         ),
 174                                                         __METHOD__
 175                                                 );
 176                                                 foreach ( $res as $row ) {
 177                                                         wfDebug( "Job with hash '{$row->job_sha1}' is a duplicate." );
 178                                                         unset( $rowSet[$row->job_sha1] ); // already enqueued
 179                                                 }
 180                                         }
 181                                         // Build the full list of job rows to insert
 182                                         $rows = array_merge( $rowList, array_values( $rowSet ) );
 183                                         // Insert the job rows in chunks to avoid slave lag...
 184                                         foreach ( array_chunk( $rows, 50 ) as $rowBatch ) {
 185                                                 $dbw->insert( 'job', $rowBatch, __METHOD__ );
 186                                         }
 187                                         wfIncrStats( 'job-insert', count( $rows ) );
 188                                         wfIncrStats( 'job-insert-duplicate',
 189                                                 count( $rowSet ) + count( $rowList ) - count( $rows ) );
 190                                 } catch ( DBError $e ) {
 191                                         if ( $atomic ) {
 192                                                 $dbw->rollback( __METHOD__ );
 193                                         }
 194                                         throw $e;
 195                                 }
 196                                 if ( $atomic ) {
 197                                         $dbw->commit( __METHOD__ );
 198                                 }
 199
 200                                 $wgMemc->set( $key, 'false', $ttl ); // queue is not empty
 201                         } );
 202                 }
 203
 204                 return true;
 205         }
 206
 207         /**
 208          * @see JobQueue::doPop()
 209          * @return Job|bool
 210          */
 211         protected function doPop() {
 212                 global $wgMemc;
 213
 214                 if ( $wgMemc->get( $this->getCacheKey( 'empty' ) ) === 'true' ) {
 215                         return false; // queue is empty
 216                 }
 217
 218                 list( $dbw, $scope ) = $this->getMasterDB();
 219                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 220
 221                 $uuid = wfRandomString( 32 ); // pop attempt
 222                 $job = false; // job popped off
 223                 do { // retry when our row is invalid or deleted as a duplicate
 224                         // Try to reserve a row in the DB...
 225                         if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
 226                                 $row = $this->claimOldest( $uuid );
 227                         } else { // random first
 228                                 $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 229                                 $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 230                                 $row  = $this->claimRandom( $uuid, $rand, $gte );
 231                         }
 232                         // Check if we found a row to reserve...
 233                         if ( !$row ) {
 234                                 $wgMemc->set( $this->getCacheKey( 'empty' ), 'true', self::CACHE_TTL_LONG );
 235                                 break; // nothing to do
 236                         }
 237                         wfIncrStats( 'job-pop' );
 238                         // Get the job object from the row...
 239                         $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 240                         if ( !$title ) {
 241                                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 242                                 wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
 243                                 continue; // try again
 244                         }
 245                         $job = Job::factory( $row->job_cmd, $title,
 246                                 self::extractBlob( $row->job_params ), $row->job_id );
 247                         $job->id = $row->job_id; // XXX: work around broken subclasses
 248                         // Flag this job as an old duplicate based on its "root" job...
 249                         if ( $this->isRootJobOldDuplicate( $job ) ) {
 250                                 wfIncrStats( 'job-pop-duplicate' );
 251                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 252                         }
 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 $uuid string 32 char hex string
 263          * @param $rand integer Random unsigned integer (31 bits)
 264          * @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
 265          * @return Row|false
 266          */
 267         protected function claimRandom( $uuid, $rand, $gte ) {
 268                 global $wgMemc;
 269
 270                 list( $dbw, $scope ) = $this->getMasterDB();
 271                 // Check cache to see if the queue has <= OFFSET items
 272                 $tinyQueue = $wgMemc->get( $this->getCacheKey( 'small' ) );
 273
 274                 $row = false; // the row acquired
 275                 $invertedDirection = false; // whether one job_random direction was already scanned
 276                 // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
 277                 // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
 278                 // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
 279                 // be used here with MySQL.
 280                 do {
 281                         if ( $tinyQueue ) { // queue has <= MAX_OFFSET rows
 282                                 // For small queues, using OFFSET will overshoot and return no rows more often.
 283                                 // Instead, this uses job_random to pick a row (possibly checking both directions).
 284                                 $ineq = $gte ? '>=' : '<=';
 285                                 $dir  = $gte ? 'ASC' : 'DESC';
 286                                 $row  = $dbw->selectRow( 'job', '*', // find a random job
 287                                         array(
 288                                                 'job_cmd'   => $this->type,
 289                                                 'job_token' => '', // unclaimed
 290                                                 "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 291                                         __METHOD__,
 292                                         array( 'ORDER BY' => "job_random {$dir}" )
 293                                 );
 294                                 if ( !$row && !$invertedDirection ) {
 295                                         $gte = !$gte;
 296                                         $invertedDirection = true;
 297                                         continue; // try the other direction
 298                                 }
 299                         } else { // table *may* have >= MAX_OFFSET rows
 300                                 // Bug 42614: "ORDER BY job_random" with a job_random inequality causes high CPU
 301                                 // in MySQL if there are many rows for some reason. This uses a small OFFSET
 302                                 // instead of job_random for reducing excess claim retries.
 303                                 $row = $dbw->selectRow( 'job', '*', // find a random job
 304                                         array(
 305                                                 'job_cmd'   => $this->type,
 306                                                 'job_token' => '', // unclaimed
 307                                         ),
 308                                         __METHOD__,
 309                                         array( 'OFFSET' => mt_rand( 0, self::MAX_OFFSET ) )
 310                                 );
 311                                 if ( !$row ) {
 312                                         $tinyQueue = true; // we know the queue must have <= MAX_OFFSET rows
 313                                         $wgMemc->set( $this->getCacheKey( 'small' ), 1, 30 );
 314                                         continue; // use job_random
 315                                 }
 316                         }
 317                         if ( $row ) { // claim the job
 318                                 $dbw->update( 'job', // update by PK
 319                                         array(
 320                                                 'job_token'           => $uuid,
 321                                                 'job_token_timestamp' => $dbw->timestamp(),
 322                                                 'job_attempts = job_attempts+1' ),
 323                                         array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
 324                                         __METHOD__
 325                                 );
 326                                 // This might get raced out by another runner when claiming the previously
 327                                 // selected row. The use of job_random should minimize this problem, however.
 328                                 if ( !$dbw->affectedRows() ) {
 329                                         $row = false; // raced out
 330                                 }
 331                         } else {
 332                                 break; // nothing to do
 333                         }
 334                 } while ( !$row );
 335
 336                 return $row;
 337         }
 338
 339         /**
 340          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 341          *
 342          * @param $uuid string 32 char hex string
 343          * @return Row|false
 344          */
 345         protected function claimOldest( $uuid ) {
 346                 list( $dbw, $scope ) = $this->getMasterDB();
 347
 348                 $row = false; // the row acquired
 349                 do {
 350                         if ( $dbw->getType() === 'mysql' ) {
 351                                 // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 352                                 // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 353                                 // Oracle and Postgre have no such limitation. However, MySQL offers an
 354                                 // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 355                                 $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
 356                                         "SET " .
 357                                                 "job_token = {$dbw->addQuotes( $uuid ) }, " .
 358                                                 "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
 359                                                 "job_attempts = job_attempts+1 " .
 360                                         "WHERE ( " .
 361                                                 "job_cmd = {$dbw->addQuotes( $this->type )} " .
 362                                                 "AND job_token = {$dbw->addQuotes( '' )} " .
 363                                         ") ORDER BY job_id ASC LIMIT 1",
 364                                         __METHOD__
 365                                 );
 366                         } else {
 367                                 // Use a subquery to find the job, within an UPDATE to claim it.
 368                                 // This uses as much of the DB wrapper functions as possible.
 369                                 $dbw->update( 'job',
 370                                         array(
 371                                                 'job_token'           => $uuid,
 372                                                 'job_token_timestamp' => $dbw->timestamp(),
 373                                                 'job_attempts = job_attempts+1' ),
 374                                         array( 'job_id = (' .
 375                                                 $dbw->selectSQLText( 'job', 'job_id',
 376                                                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
 377                                                         __METHOD__,
 378                                                         array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
 379                                                 ')'
 380                                         ),
 381                                         __METHOD__
 382                                 );
 383                         }
 384                         // Fetch any row that we just reserved...
 385                         if ( $dbw->affectedRows() ) {
 386                                 $row = $dbw->selectRow( 'job', '*',
 387                                         array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
 388                                 );
 389                                 if ( !$row ) { // raced out by duplicate job removal
 390                                         wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
 391                                 }
 392                         } else {
 393                                 break; // nothing to do
 394                         }
 395                 } while ( !$row );
 396
 397                 return $row;
 398         }
 399
 400         /**
 401          * Recycle or destroy any jobs that have been claimed for too long
 402          *
 403          * @return integer Number of jobs recycled/deleted
 404          */
 405         public function recycleAndDeleteStaleJobs() {
 406                 global $wgMemc;
 407
 408                 $now = time();
 409                 list( $dbw, $scope ) = $this->getMasterDB();
 410                 $count = 0; // affected rows
 411
 412                 if ( !$dbw->lock( "jobqueue-recycle-{$this->type}", __METHOD__, 1 ) ) {
 413                         return $count; // already in progress
 414                 }
 415
 416                 // Remove claims on jobs acquired for too long if enabled...
 417                 if ( $this->claimTTL > 0 ) {
 418                         $claimCutoff = $dbw->timestamp( $now - $this->claimTTL );
 419                         // Get the IDs of jobs that have be claimed but not finished after too long.
 420                         // These jobs can be recycled into the queue by expiring the claim. Selecting
 421                         // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
 422                         $res = $dbw->select( 'job', 'job_id',
 423                                 array(
 424                                         'job_cmd' => $this->type,
 425                                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 426                                         "job_token_timestamp < {$dbw->addQuotes( $claimCutoff )}", // stale
 427                                         "job_attempts < {$dbw->addQuotes( self::MAX_ATTEMPTS )}" ), // retries left
 428                                 __METHOD__
 429                         );
 430                         $ids = array_map( function( $o ) { return $o->job_id; }, iterator_to_array( $res ) );
 431                         if ( count( $ids ) ) {
 432                                 // Reset job_token for these jobs so that other runners will pick them up.
 433                                 // Set the timestamp to the current time, as it is useful to now that the job
 434                                 // was already tried before (the timestamp becomes the "released" time).
 435                                 $dbw->update( 'job',
 436                                         array(
 437                                                 'job_token' => '',
 438                                                 'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
 439                                         array(
 440                                                 'job_id' => $ids ),
 441                                         __METHOD__
 442                                 );
 443                                 $count += $dbw->affectedRows();
 444                                 wfIncrStats( 'job-recycle', $dbw->affectedRows() );
 445                                 $wgMemc->set( $this->getCacheKey( 'empty' ), 'false', self::CACHE_TTL_LONG );
 446                         }
 447                 }
 448
 449                 // Just destroy any stale jobs...
 450                 $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
 451                 $conds = array(
 452                         'job_cmd' => $this->type,
 453                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 454                         "job_token_timestamp < {$dbw->addQuotes( $pruneCutoff )}" // stale
 455                 );
 456                 if ( $this->claimTTL > 0 ) { // only prune jobs attempted too many times...
 457                         $conds[] = "job_attempts >= {$dbw->addQuotes( self::MAX_ATTEMPTS )}";
 458                 }
 459                 // Get the IDs of jobs that are considered stale and should be removed. Selecting
 460                 // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
 461                 $res = $dbw->select( 'job', 'job_id', $conds, __METHOD__ );
 462                 $ids = array_map( function( $o ) { return $o->job_id; }, iterator_to_array( $res ) );
 463                 if ( count( $ids ) ) {
 464                         $dbw->delete( 'job', array( 'job_id' => $ids ), __METHOD__ );
 465                         $count += $dbw->affectedRows();
 466                 }
 467
 468                 $dbw->unlock( "jobqueue-recycle-{$this->type}", __METHOD__ );
 469
 470                 return $count;
 471         }
 472
 473         /**
 474          * @see JobQueue::doAck()
 475          * @param Job $job
 476          * @throws MWException
 477          * @return Job|bool
 478          */
 479         protected function doAck( Job $job ) {
 480                 if ( !$job->getId() ) {
 481                         throw new MWException( "Job of type '{$job->getType()}' has no ID." );
 482                 }
 483
 484                 list( $dbw, $scope ) = $this->getMasterDB();
 485                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 486
 487                 // Delete a row with a single DELETE without holding row locks over RTTs...
 488                 $dbw->delete( 'job',
 489                         array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ), __METHOD__ );
 490
 491                 return true;
 492         }
 493
 494         /**
 495          * @see JobQueue::doDeduplicateRootJob()
 496          * @param Job $job
 497          * @throws MWException
 498          * @return bool
 499          */
 500         protected function doDeduplicateRootJob( Job $job ) {
 501                 $params = $job->getParams();
 502                 if ( !isset( $params['rootJobSignature'] ) ) {
 503                         throw new MWException( "Cannot register root job; missing 'rootJobSignature'." );
 504                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 505                         throw new MWException( "Cannot register root job; missing 'rootJobTimestamp'." );
 506                 }
 507                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 508                 // Callers should call batchInsert() and then this function so that if the insert
 509                 // fails, the de-duplication registration will be aborted. Since the insert is
 510                 // deferred till "transaction idle", do the same here, so that the ordering is
 511                 // maintained. Having only the de-duplication registration succeed would cause
 512                 // jobs to become no-ops without any actual jobs that made them redundant.
 513                 list( $dbw, $scope ) = $this->getMasterDB();
 514                 $dbw->onTransactionIdle( function() use ( $params, $key, $scope ) {
 515                         global $wgMemc;
 516
 517                         $timestamp = $wgMemc->get( $key ); // current last timestamp of this job
 518                         if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 519                                 return true; // a newer version of this root job was enqueued
 520                         }
 521
 522                         // Update the timestamp of the last root job started at the location...
 523                         return $wgMemc->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 524                 } );
 525
 526                 return true;
 527         }
 528
 529         /**
 530          * Check if the "root" job of a given job has been superseded by a newer one
 531          *
 532          * @param $job Job
 533          * @return bool
 534          */
 535         protected function isRootJobOldDuplicate( Job $job ) {
 536                 global $wgMemc;
 537
 538                 $params = $job->getParams();
 539                 if ( !isset( $params['rootJobSignature'] ) ) {
 540                         return false; // job has no de-deplication info
 541                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 542                         trigger_error( "Cannot check root job; missing 'rootJobTimestamp'." );
 543                         return false;
 544                 }
 545
 546                 // Get the last time this root job was enqueued
 547                 $timestamp = $wgMemc->get( $this->getRootJobCacheKey( $params['rootJobSignature'] ) );
 548
 549                 // Check if a new root job was started at the location after this one's...
 550                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 551         }
 552
 553         /**
 554          * @see JobQueue::doWaitForBackups()
 555          * @return void
 556          */
 557         protected function doWaitForBackups() {
 558                 wfWaitForSlaves();
 559         }
 560
 561         /**
 562          * @return Array
 563          */
 564         protected function doGetPeriodicTasks() {
 565                 return array(
 566                         'recycleAndDeleteStaleJobs' => array(
 567                                 'callback' => array( $this, 'recycleAndDeleteStaleJobs' ),
 568                                 'period'   => ceil( $this->claimTTL / 2 )
 569                         )
 570                 );
 571         }
 572
 573         /**
 574          * @return void
 575          */
 576         protected function doFlushCaches() {
 577                 global $wgMemc;
 578
 579                 foreach ( array( 'empty', 'size', 'acquiredcount' ) as $type ) {
 580                         $wgMemc->delete( $this->getCacheKey( $type ) );
 581                 }
 582         }
 583
 584         /**
 585          * @return Array (DatabaseBase, ScopedCallback)
 586          */
 587         protected function getSlaveDB() {
 588                 return $this->getDB( DB_SLAVE );
 589         }
 590
 591         /**
 592          * @return Array (DatabaseBase, ScopedCallback)
 593          */
 594         protected function getMasterDB() {
 595                 return $this->getDB( DB_MASTER );
 596         }
 597
 598         /**
 599          * @param $index integer (DB_SLAVE/DB_MASTER)
 600          * @return Array (DatabaseBase, ScopedCallback)
 601          */
 602         protected function getDB( $index ) {
 603                 $lb = ( $this->cluster !== false )
 604                         ? wfGetLBFactory()->getExternalLB( $this->cluster, $this->wiki )
 605                         : wfGetLB( $this->wiki );
 606                 $conn = $lb->getConnection( $index, array(), $this->wiki );
 607                 return array(
 608                         $conn,
 609                         new ScopedCallback( function() use ( $lb, $conn ) {
 610                                 $lb->reuseConnection( $conn );
 611                         } )
 612                 );
 613         }
 614
 615         /**
 616          * @param $job Job
 617          * @return array
 618          */
 619         protected function insertFields( Job $job ) {
 620                 list( $dbw, $scope ) = $this->getMasterDB();
 621                 return array(
 622                         // Fields that describe the nature of the job
 623                         'job_cmd'       => $job->getType(),
 624                         'job_namespace' => $job->getTitle()->getNamespace(),
 625                         'job_title'     => $job->getTitle()->getDBkey(),
 626                         'job_params'    => self::makeBlob( $job->getParams() ),
 627                         // Additional job metadata
 628                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 629                         'job_timestamp' => $dbw->timestamp(),
 630                         'job_sha1'      => wfBaseConvert(
 631                                 sha1( serialize( $job->getDeduplicationInfo() ) ),
 632                                 16, 36, 31
 633                         ),
 634                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 635                 );
 636         }
 637
 638         /**
 639          * @return string
 640          */
 641         private function getCacheKey( $property ) {
 642                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 643                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, $property );
 644         }
 645
 646         /**
 647          * @param string $signature Hash identifier of the root job
 648          * @return string
 649          */
 650         private function getRootJobCacheKey( $signature ) {
 651                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 652                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 653         }
 654
 655         /**
 656          * @param $params
 657          * @return string
 658          */
 659         protected static function makeBlob( $params ) {
 660                 if ( $params !== false ) {
 661                         return serialize( $params );
 662                 } else {
 663                         return '';
 664                 }
 665         }
 666
 667         /**
 668          * @param $blob
 669          * @return bool|mixed
 670          */
 671         protected static function extractBlob( $blob ) {
 672                 if ( (string)$blob !== '' ) {
 673                         return unserialize( $blob );
 674                 } else {
 675                         return false;
 676                 }
 677         }
 678 }