includes/job/JobQueueDB.php

   1 <?php
   2 /**
   3  * Database-backed job queue code.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @author Aaron Schulz
  22  */
  23
  24 /**
  25  * Class to handle job queues stored in the DB
  26  *
  27  * @ingroup JobQueue
  28  * @since 1.21
  29  */
  30 class JobQueueDB extends JobQueue {
  31         const CACHE_TTL      = 300; // integer; seconds to cache queue information
  32         const MAX_AGE_PRUNE  = 604800; // integer; seconds a job can live once claimed
  33         const MAX_ATTEMPTS   = 3; // integer; number of times to try a job
  34         const MAX_JOB_RANDOM = 2147483647; // integer; 2^31 - 1, used for job_random
  35
  36         /**
  37          * @see JobQueue::doIsEmpty()
  38          * @return bool
  39          */
  40         protected function doIsEmpty() {
  41                 global $wgMemc;
  42
  43                 $key = $this->getEmptinessCacheKey();
  44
  45                 $isEmpty = $wgMemc->get( $key );
  46                 if ( $isEmpty === 'true' ) {
  47                         return true;
  48                 } elseif ( $isEmpty === 'false' ) {
  49                         return false;
  50                 }
  51
  52                 $found = $this->getSlaveDB()->selectField(
  53                         'job', '1', array( 'job_cmd' => $this->type ), __METHOD__
  54                 );
  55
  56                 $wgMemc->add( $key, $found ? 'false' : 'true', self::CACHE_TTL );
  57         }
  58
  59         /**
  60          * @see JobQueue::doBatchPush()
  61          * @return bool
  62          */
  63         protected function doBatchPush( array $jobs, $flags ) {
  64                 if ( count( $jobs ) ) {
  65                         $dbw = $this->getMasterDB();
  66
  67                         $rows = array();
  68                         foreach ( $jobs as $job ) {
  69                                 $rows[] = $this->insertFields( $job );
  70                         }
  71                         $atomic = ( $flags & self::QoS_Atomic );
  72                         $key    = $this->getEmptinessCacheKey();
  73                         $ttl    = self::CACHE_TTL;
  74
  75                         $dbw->onTransactionIdle( function() use ( $dbw, $rows, $atomic, $key, $ttl ) {
  76                                 global $wgMemc;
  77
  78                                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
  79                                 if ( $atomic ) {
  80                                         $dbw->begin(); // wrap all the job additions in one transaction
  81                                 } else {
  82                                         $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
  83                                 }
  84                                 try {
  85                                         foreach ( array_chunk( $rows, 50 ) as $rowBatch ) { // avoid slave lag
  86                                                 $dbw->insert( 'job', $rowBatch, __METHOD__ );
  87                                         }
  88                                 } catch ( DBError $e ) {
  89                                         if ( $atomic ) {
  90                                                 $dbw->rollback();
  91                                         } else {
  92                                                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
  93                                         }
  94                                         throw $e;
  95                                 }
  96                                 if ( $atomic ) {
  97                                         $dbw->commit();
  98                                 } else {
  99                                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 100                                 }
 101
 102                                 $wgMemc->set( $key, 'false', $ttl ); // queue is not empty
 103                         } );
 104                 }
 105
 106                 return true;
 107         }
 108
 109         /**
 110          * @see JobQueue::doPop()
 111          * @return Job|bool
 112          */
 113         protected function doPop() {
 114                 global $wgMemc;
 115
 116                 if ( $wgMemc->get( $this->getEmptinessCacheKey() ) === 'true' ) {
 117                         return false; // queue is empty
 118                 }
 119
 120                 $dbw = $this->getMasterDB();
 121                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 122
 123                 $uuid = wfRandomString( 32 ); // pop attempt
 124                 $job = false; // job popped off
 125                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
 126                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 127                 try {
 128                         // Occasionally recycle jobs back into the queue that have been claimed too long
 129                         if ( mt_rand( 0, 99 ) == 0 ) {
 130                                 $this->recycleStaleJobs();
 131                         }
 132                         do { // retry when our row is invalid or deleted as a duplicate
 133                                 // Try to reserve a row in the DB...
 134                                 if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
 135                                         $row = $this->claimOldest( $uuid );
 136                                 } else { // random first
 137                                         $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
 138                                         $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
 139                                         $row  = $this->claimRandom( $uuid, $rand, $gte );
 140                                         if ( !$row ) { // need to try the other direction
 141                                                 $row = $this->claimRandom( $uuid, $rand, !$gte );
 142                                         }
 143                                 }
 144                                 // Check if we found a row to reserve...
 145                                 if ( !$row ) {
 146                                         $wgMemc->set( $this->getEmptinessCacheKey(), 'true', self::CACHE_TTL );
 147                                         break; // nothing to do
 148                                 }
 149                                 // Get the job object from the row...
 150                                 $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
 151                                 if ( !$title ) {
 152                                         $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 153                                         wfIncrStats( 'job-pop' );
 154                                         wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
 155                                         continue; // try again
 156                                 }
 157                                 $job = Job::factory( $row->job_cmd, $title,
 158                                         self::extractBlob( $row->job_params ), $row->job_id );
 159                                 // Delete any *other* duplicate jobs in the queue...
 160                                 if ( $job->ignoreDuplicates() && strlen( $row->job_sha1 ) ) {
 161                                         $dbw->delete( 'job',
 162                                                 array( 'job_sha1' => $row->job_sha1,
 163                                                         "job_id != {$dbw->addQuotes( $row->job_id )}" ),
 164                                                 __METHOD__
 165                                         );
 166                                         wfIncrStats( 'job-pop', $dbw->affectedRows() );
 167                                 }
 168                                 break; // done
 169                         } while( true );
 170                 } catch ( DBError $e ) {
 171                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 172                         throw $e;
 173                 }
 174                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 175
 176                 return $job;
 177         }
 178
 179         /**
 180          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 181          *
 182          * @param $uuid string 32 char hex string
 183          * @param $rand integer Random unsigned integer (31 bits)
 184          * @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
 185          * @return Row|false
 186          */
 187         protected function claimRandom( $uuid, $rand, $gte ) {
 188                 $dbw  = $this->getMasterDB();
 189                 $dir  = $gte ? 'ASC' : 'DESC';
 190                 $ineq = $gte ? '>=' : '<=';
 191
 192                 $row = false; // the row acquired
 193                 // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
 194                 // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
 195                 // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
 196                 // be used here with MySQL.
 197                 do {
 198                         $row = $dbw->selectRow( 'job', '*', // find a random job
 199                                 array(
 200                                         'job_cmd'   => $this->type,
 201                                         'job_token' => '',
 202                                         "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
 203                                 __METHOD__,
 204                                 array( 'ORDER BY' => "job_random {$dir}" )
 205                         );
 206                         if ( $row ) { // claim the job
 207                                 $dbw->update( 'job', // update by PK
 208                                         array(
 209                                                 'job_token'           => $uuid,
 210                                                 'job_token_timestamp' => $dbw->timestamp(),
 211                                                 'job_attempts = job_attempts+1' ),
 212                                         array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
 213                                         __METHOD__
 214                                 );
 215                                 // This might get raced out by another runner when claiming the previously
 216                                 // selected row. The use of job_random should minimize this problem, however.
 217                                 if ( !$dbw->affectedRows() ) {
 218                                         $row = false; // raced out
 219                                 }
 220                         } else {
 221                                 break; // nothing to do
 222                         }
 223                 } while ( !$row );
 224
 225                 return $row;
 226         }
 227
 228         /**
 229          * Reserve a row with a single UPDATE without holding row locks over RTTs...
 230          *
 231          * @param $uuid string 32 char hex string
 232          * @return Row|false
 233          */
 234         protected function claimOldest( $uuid ) {
 235                 $dbw  = $this->getMasterDB();
 236
 237                 $row = false; // the row acquired
 238                 do {
 239                         if ( $dbw->getType() === 'mysql' ) {
 240                                 // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
 241                                 // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
 242                                 // Oracle and Postgre have no such limitation. However, MySQL offers an
 243                                 // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
 244                                 $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
 245                                         "SET " .
 246                                                 "job_token = {$dbw->addQuotes( $uuid ) }, " .
 247                                                 "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
 248                                                 "job_attempts = job_attempts+1 " .
 249                                         "WHERE ( " .
 250                                                 "job_cmd = {$dbw->addQuotes( $this->type )} " .
 251                                                 "AND job_token = {$dbw->addQuotes( '' )} " .
 252                                         ") ORDER BY job_id ASC LIMIT 1",
 253                                         __METHOD__
 254                                 );
 255                         } else {
 256                                 // Use a subquery to find the job, within an UPDATE to claim it.
 257                                 // This uses as much of the DB wrapper functions as possible.
 258                                 $dbw->update( 'job',
 259                                         array(
 260                                                 'job_token'           => $uuid,
 261                                                 'job_token_timestamp' => $dbw->timestamp(),
 262                                                 'job_attempts = job_attempts+1' ),
 263                                         array( 'job_id = (' .
 264                                                 $dbw->selectSQLText( 'job', 'job_id',
 265                                                         array( 'job_cmd' => $this->type, 'job_token' => '' ),
 266                                                         __METHOD__,
 267                                                         array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
 268                                                 ')'
 269                                         ),
 270                                         __METHOD__
 271                                 );
 272                         }
 273                         // Fetch any row that we just reserved...
 274                         if ( $dbw->affectedRows() ) {
 275                                 $row = $dbw->selectRow( 'job', '*',
 276                                         array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
 277                                 );
 278                                 if ( !$row ) { // raced out by duplicate job removal
 279                                         wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
 280                                 }
 281                         } else {
 282                                 break; // nothing to do
 283                         }
 284                 } while ( !$row );
 285
 286                 return $row;
 287         }
 288
 289         /**
 290          * Recycle or destroy any jobs that have been claimed for too long
 291          *
 292          * @return integer Number of jobs recycled/deleted
 293          */
 294         protected function recycleStaleJobs() {
 295                 $now    = time();
 296                 $dbw    = $this->getMasterDB();
 297
 298                 if ( $this->claimTTL > 0 ) { // re-try stale jobs...
 299                         $claimCutoff = $dbw->timestamp( $now - $this->claimTTL );
 300                         // Reset job_token for these jobs so that other runners will pick them up.
 301                         // Set the timestamp to the current time, as it is useful to now that the job
 302                         // was already tried before.
 303                         $dbw->update( 'job',
 304                                 array(
 305                                         'job_token' => '',
 306                                         'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
 307                                 array(
 308                                         'job_cmd' => $this->type,
 309                                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 310                                         "job_token_timestamp < {$dbw->addQuotes( $claimCutoff )}", // stale
 311                                         "job_attempts < {$dbw->addQuotes( self::MAX_ATTEMPTS )}" ),
 312                                 __METHOD__
 313                         );
 314                 }
 315
 316                 // Just destroy stale jobs...
 317                 $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
 318                 $conds = array(
 319                         'job_cmd' => $this->type,
 320                         "job_token != {$dbw->addQuotes( '' )}", // was acquired
 321                         "job_token_timestamp < {$dbw->addQuotes( $pruneCutoff )}" // stale
 322                 );
 323                 if ( $this->claimTTL > 0 ) { // only prune jobs attempted too many times...
 324                         $conds[] = "job_attempts >= {$dbw->addQuotes( self::MAX_ATTEMPTS )}";
 325                 }
 326
 327                 return $dbw->affectedRows();
 328         }
 329
 330         /**
 331          * @see JobQueue::doAck()
 332          * @return Job|bool
 333          */
 334         protected function doAck( Job $job ) {
 335                 $dbw = $this->getMasterDB();
 336                 $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 337
 338                 $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
 339                 $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
 340                 try {
 341                         // Delete a row with a single DELETE without holding row locks over RTTs...
 342                         $dbw->delete( 'job', array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ) );
 343                 } catch ( Exception $e ) {
 344                         $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 345                         throw $e;
 346                 }
 347                 $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
 348
 349                 return true;
 350         }
 351
 352         /**
 353          * @see JobQueue::doWaitForBackups()
 354          * @return void
 355          */
 356         protected function doWaitForBackups() {
 357                 wfWaitForSlaves();
 358         }
 359
 360         /**
 361          * @return DatabaseBase
 362          */
 363         protected function getSlaveDB() {
 364                 return wfGetDB( DB_SLAVE, array(), $this->wiki );
 365         }
 366
 367         /**
 368          * @return DatabaseBase
 369          */
 370         protected function getMasterDB() {
 371                 return wfGetDB( DB_MASTER, array(), $this->wiki );
 372         }
 373
 374         /**
 375          * @param $job Job
 376          * @return array
 377          */
 378         protected function insertFields( Job $job ) {
 379                 // Rows that describe the nature of the job
 380                 $descFields = array(
 381                         'job_cmd'       => $job->getType(),
 382                         'job_namespace' => $job->getTitle()->getNamespace(),
 383                         'job_title'     => $job->getTitle()->getDBkey(),
 384                         'job_params'    => self::makeBlob( $job->getParams() ),
 385                 );
 386                 // Additional job metadata
 387                 $dbw = $this->getMasterDB();
 388                 $metaFields = array(
 389                         'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 390                         'job_timestamp' => $dbw->timestamp(),
 391                         'job_sha1'      => wfBaseConvert( sha1( serialize( $descFields ) ), 16, 36, 32 ),
 392                         'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
 393                 );
 394                 return ( $descFields + $metaFields );
 395         }
 396
 397         /**
 398          * @return string
 399          */
 400         private function getEmptinessCacheKey() {
 401                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 402                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'isempty' );
 403         }
 404
 405         /**
 406          * @param $params
 407          * @return string
 408          */
 409         protected static function makeBlob( $params ) {
 410                 if ( $params !== false ) {
 411                         return serialize( $params );
 412                 } else {
 413                         return '';
 414                 }
 415         }
 416
 417         /**
 418          * @param $blob
 419          * @return bool|mixed
 420          */
 421         protected static function extractBlob( $blob ) {
 422                 if ( (string)$blob !== '' ) {
 423                         return unserialize( $blob );
 424                 } else {
 425                         return false;
 426                 }
 427         }
 428 }