[JobQueue] Clarified documentation a bit.
[lhc/web/wiklou.git] / includes / job / JobQueueDB.php
index cbb2391..14c1dca 100644 (file)
@@ -49,54 +49,80 @@ class JobQueueDB extends JobQueue {
                        return false;
                }
 
-               $found = $this->getSlaveDB()->selectField(
-                       'job', '1', array( 'job_cmd' => $this->type ), __METHOD__
+               $found = $this->getSlaveDB()->selectField( // unclaimed job
+                       'job', '1', array( 'job_cmd' => $this->type, 'job_token' => '' ), __METHOD__
                );
-
                $wgMemc->add( $key, $found ? 'false' : 'true', self::CACHE_TTL );
+
+               return !$found;
        }
 
        /**
         * @see JobQueue::doBatchPush()
+        * @param array $jobs
+        * @param $flags
+        * @throws DBError|Exception
         * @return bool
         */
        protected function doBatchPush( array $jobs, $flags ) {
                if ( count( $jobs ) ) {
                        $dbw = $this->getMasterDB();
 
-                       $rows = array();
+                       $rowSet = array(); // (sha1 => job) map for jobs that are de-duplicated
+                       $rowList = array(); // list of jobs for jobs that are are not de-duplicated
+
                        foreach ( $jobs as $job ) {
-                               $rows[] = $this->insertFields( $job );
+                               $row = $this->insertFields( $job );
+                               if ( $job->ignoreDuplicates() ) {
+                                       $rowSet[$row['job_sha1']] = $row;
+                               } else {
+                                       $rowList[] = $row;
+                               }
                        }
+
                        $atomic = ( $flags & self::QoS_Atomic );
                        $key    = $this->getEmptinessCacheKey();
                        $ttl    = self::CACHE_TTL;
 
-                       $dbw->onTransactionIdle( function() use ( $dbw, $rows, $atomic, $key, $ttl ) {
+                       $dbw->onTransactionIdle(
+                               function() use ( $dbw, $rowSet, $rowList, $atomic, $key, $ttl
+                       ) {
                                global $wgMemc;
 
-                               $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
                                if ( $atomic ) {
-                                       $dbw->begin(); // wrap all the job additions in one transaction
-                               } else {
-                                       $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
+                                       $dbw->begin( __METHOD__ ); // wrap all the job additions in one transaction
                                }
                                try {
-                                       foreach ( array_chunk( $rows, 50 ) as $rowBatch ) { // avoid slave lag
+                                       // Strip out any duplicate jobs that are already in the queue...
+                                       if ( count( $rowSet ) ) {
+                                               $res = $dbw->select( 'job', 'job_sha1',
+                                                       array(
+                                                               // No job_type condition since it's part of the job_sha1 hash
+                                                               'job_sha1'  => array_keys( $rowSet ),
+                                                               'job_token' => '' // unclaimed
+                                                       ),
+                                                       __METHOD__
+                                               );
+                                               foreach ( $res as $row ) {
+                                                       wfDebug( "Job with hash '{$row->job_sha1}' is a duplicate." );
+                                                       unset( $rowSet[$row->job_sha1] ); // already enqueued
+                                               }
+                                       }
+                                       // Build the full list of job rows to insert
+                                       $rows = array_merge( $rowList, array_values( $rowSet ) );
+                                       // Insert the job rows in chunks to avoid slave lag...
+                                       foreach ( array_chunk( $rows, 50 ) as $rowBatch ) {
                                                $dbw->insert( 'job', $rowBatch, __METHOD__ );
                                        }
+                                       wfIncrStats( 'job-insert', count( $rows ) );
                                } catch ( DBError $e ) {
                                        if ( $atomic ) {
-                                               $dbw->rollback();
-                                       } else {
-                                               $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
+                                               $dbw->rollback( __METHOD__ );
                                        }
                                        throw $e;
                                }
                                if ( $atomic ) {
-                                       $dbw->commit();
-                               } else {
-                                       $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
+                                       $dbw->commit( __METHOD__ );
                                }
 
                                $wgMemc->set( $key, 'false', $ttl ); // queue is not empty
@@ -122,56 +148,44 @@ class JobQueueDB extends JobQueue {
 
                $uuid = wfRandomString( 32 ); // pop attempt
                $job = false; // job popped off
-               $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
-               $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
-               try {
-                       // Occasionally recycle jobs back into the queue that have been claimed too long
-                       if ( mt_rand( 0, 99 ) == 0 ) {
-                               $this->recycleStaleJobs();
-                       }
-                       do { // retry when our row is invalid or deleted as a duplicate
-                               // Try to reserve a row in the DB...
-                               if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
-                                       $row = $this->claimOldest( $uuid );
-                               } else { // random first
-                                       $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
-                                       $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
-                                       $row  = $this->claimRandom( $uuid, $rand, $gte );
-                                       if ( !$row ) { // need to try the other direction
-                                               $row = $this->claimRandom( $uuid, $rand, !$gte );
-                                       }
-                               }
-                               // Check if we found a row to reserve...
-                               if ( !$row ) {
-                                       $wgMemc->set( $this->getEmptinessCacheKey(), 'true', self::CACHE_TTL );
-                                       break; // nothing to do
-                               }
-                               // Get the job object from the row...
-                               $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
-                               if ( !$title ) {
-                                       $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
-                                       wfIncrStats( 'job-pop' );
-                                       wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
-                                       continue; // try again
-                               }
-                               $job = Job::factory( $row->job_cmd, $title,
-                                       self::extractBlob( $row->job_params ), $row->job_id );
-                               // Delete any *other* duplicate jobs in the queue...
-                               if ( $job->ignoreDuplicates() && strlen( $row->job_sha1 ) ) {
-                                       $dbw->delete( 'job',
-                                               array( 'job_sha1' => $row->job_sha1,
-                                                       "job_id != {$dbw->addQuotes( $row->job_id )}" ),
-                                               __METHOD__
-                                       );
-                                       wfIncrStats( 'job-pop', $dbw->affectedRows() );
-                               }
-                               break; // done
-                       } while( true );
-               } catch ( DBError $e ) {
-                       $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
-                       throw $e;
+               // Occasionally recycle jobs back into the queue that have been claimed too long
+               if ( mt_rand( 0, 99 ) == 0 ) {
+                       $this->recycleStaleJobs();
                }
-               $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
+               do { // retry when our row is invalid or deleted as a duplicate
+                       // Try to reserve a row in the DB...
+                       if ( in_array( $this->order, array( 'fifo', 'timestamp' ) ) ) {
+                               $row = $this->claimOldest( $uuid );
+                       } else { // random first
+                               $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
+                               $gte  = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
+                               $row  = $this->claimRandom( $uuid, $rand, $gte );
+                               if ( !$row ) { // need to try the other direction
+                                       $row = $this->claimRandom( $uuid, $rand, !$gte );
+                               }
+                       }
+                       // Check if we found a row to reserve...
+                       if ( !$row ) {
+                               $wgMemc->set( $this->getEmptinessCacheKey(), 'true', self::CACHE_TTL );
+                               break; // nothing to do
+                       }
+                       wfIncrStats( 'job-pop' );
+                       // Get the job object from the row...
+                       $title = Title::makeTitleSafe( $row->job_namespace, $row->job_title );
+                       if ( !$title ) {
+                               $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
+                               wfDebugLog( 'JobQueueDB', "Row has invalid title '{$row->job_title}'." );
+                               continue; // try again
+                       }
+                       $job = Job::factory( $row->job_cmd, $title,
+                               self::extractBlob( $row->job_params ), $row->job_id );
+                       $job->id = $row->job_id; // XXX: work around broken subclasses
+                       // Flag this job as an old duplicate based on its "root" job...
+                       if ( $this->isRootJobOldDuplicate( $job ) ) {
+                               $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
+                       }
+                       break; // done
+               } while( true );
 
                return $job;
        }
@@ -186,7 +200,6 @@ class JobQueueDB extends JobQueue {
         */
        protected function claimRandom( $uuid, $rand, $gte ) {
                $dbw  = $this->getMasterDB();
-               $dir  = $gte ? 'ASC' : 'DESC';
                $ineq = $gte ? '>=' : '<=';
 
                $row = false; // the row acquired
@@ -200,8 +213,8 @@ class JobQueueDB extends JobQueue {
                                        'job_cmd'   => $this->type,
                                        'job_token' => '',
                                        "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
-                               __METHOD__,
-                               array( 'ORDER BY' => "job_random {$dir}" )
+                               __METHOD__
+                               // Bug 42614: "ORDER BY job_random" causes slowness on mysql for some reason
                        );
                        if ( $row ) { // claim the job
                                $dbw->update( 'job', // update by PK
@@ -296,26 +309,42 @@ class JobQueueDB extends JobQueue {
                $dbw   = $this->getMasterDB();
                $count = 0; // affected rows
 
-               if ( $this->claimTTL > 0 ) { // re-try stale jobs...
+               if ( !$dbw->lock( "jobqueue-recycle-{$this->type}", __METHOD__, 1 ) ) {
+                       return $count; // already in progress
+               }
+
+               // Remove claims on jobs acquired for too long if enabled...
+               if ( $this->claimTTL > 0 ) {
                        $claimCutoff = $dbw->timestamp( $now - $this->claimTTL );
-                       // Reset job_token for these jobs so that other runners will pick them up.
-                       // Set the timestamp to the current time, as it is useful to now that the job
-                       // was already tried before.
-                       $dbw->update( 'job',
-                               array(
-                                       'job_token' => '',
-                                       'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
+                       // Get the IDs of jobs that have be claimed but not finished after too long.
+                       // These jobs can be recycled into the queue by expiring the claim. Selecting
+                       // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
+                       $res = $dbw->select( 'job', 'job_id',
                                array(
                                        'job_cmd' => $this->type,
                                        "job_token != {$dbw->addQuotes( '' )}", // was acquired
                                        "job_token_timestamp < {$dbw->addQuotes( $claimCutoff )}", // stale
-                                       "job_attempts < {$dbw->addQuotes( self::MAX_ATTEMPTS )}" ),
+                                       "job_attempts < {$dbw->addQuotes( self::MAX_ATTEMPTS )}" ), // retries left
                                __METHOD__
                        );
-                       $count += $dbw->affectedRows();
+                       $ids = array_map( function( $o ) { return $o->job_id; }, iterator_to_array( $res ) );
+                       if ( count( $ids ) ) {
+                               // Reset job_token for these jobs so that other runners will pick them up.
+                               // Set the timestamp to the current time, as it is useful to now that the job
+                               // was already tried before (the timestamp becomes the "released" time).
+                               $dbw->update( 'job',
+                                       array(
+                                               'job_token' => '',
+                                               'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
+                                       array(
+                                               'job_id' => $ids ),
+                                       __METHOD__
+                               );
+                               $count += $dbw->affectedRows();
+                       }
                }
 
-               // Just destroy stale jobs...
+               // Just destroy any stale jobs...
                $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
                $conds = array(
                        'job_cmd' => $this->type,
@@ -325,34 +354,99 @@ class JobQueueDB extends JobQueue {
                if ( $this->claimTTL > 0 ) { // only prune jobs attempted too many times...
                        $conds[] = "job_attempts >= {$dbw->addQuotes( self::MAX_ATTEMPTS )}";
                }
-               $dbw->delete( 'job', $conds, __METHOD__ );
-               $count += $dbw->affectedRows();
+               // Get the IDs of jobs that are considered stale and should be removed. Selecting
+               // the IDs first means that the UPDATE can be done by primary key (less deadlocks).
+               $res = $dbw->select( 'job', 'job_id', $conds, __METHOD__ );
+               $ids = array_map( function( $o ) { return $o->job_id; }, iterator_to_array( $res ) );
+               if ( count( $ids ) ) {
+                       $dbw->delete( 'job', array( 'job_id' => $ids ), __METHOD__ );
+                       $count += $dbw->affectedRows();
+               }
+
+               $dbw->unlock( "jobqueue-recycle-{$this->type}", __METHOD__ );
 
                return $count;
        }
 
        /**
         * @see JobQueue::doAck()
+        * @param Job $job
+        * @throws MWException
         * @return Job|bool
         */
        protected function doAck( Job $job ) {
+               if ( !$job->getId() ) {
+                       throw new MWException( "Job of type '{$job->getType()}' has no ID." );
+               }
+
                $dbw = $this->getMasterDB();
                $dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
 
-               $autoTrx = $dbw->getFlag( DBO_TRX ); // automatic begin() enabled?
-               $dbw->clearFlag( DBO_TRX ); // make each query its own transaction
-               try {
-                       // Delete a row with a single DELETE without holding row locks over RTTs...
-                       $dbw->delete( 'job', array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ) );
-               } catch ( Exception $e ) {
-                       $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
-                       throw $e;
+               // Delete a row with a single DELETE without holding row locks over RTTs...
+               $dbw->delete( 'job',
+                       array( 'job_cmd' => $this->type, 'job_id' => $job->getId() ), __METHOD__ );
+
+               return true;
+       }
+
+       /**
+        * @see JobQueue::doDeduplicateRootJob()
+        * @param Job $job
+        * @throws MWException
+        * @return bool
+        */
+       protected function doDeduplicateRootJob( Job $job ) {
+               $params = $job->getParams();
+               if ( !isset( $params['rootJobSignature'] ) ) {
+                       throw new MWException( "Cannot register root job; missing 'rootJobSignature'." );
+               } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
+                       throw new MWException( "Cannot register root job; missing 'rootJobTimestamp'." );
                }
-               $dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
+               $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
+               // Callers should call batchInsert() and then this function so that if the insert
+               // fails, the de-duplication registration will be aborted. Since the insert is
+               // deferred till "transaction idle", do the same here, so that the ordering is
+               // maintained. Having only the de-duplication registration succeed would cause
+               // jobs to become no-ops without any actual jobs that made them redundant.
+               $this->getMasterDB()->onTransactionIdle( function() use ( $params, $key ) {
+                       global $wgMemc;
+
+                       $timestamp = $wgMemc->get( $key ); // current last timestamp of this job
+                       if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
+                               return true; // a newer version of this root job was enqueued
+                       }
+
+                       // Update the timestamp of the last root job started at the location...
+                       return $wgMemc->set( $key, $params['rootJobTimestamp'], 14*86400 ); // 2 weeks
+               } );
 
                return true;
        }
 
+       /**
+        * Check if the "root" job of a given job has been superseded by a newer one
+        *
+        * @param $job Job
+        * @return bool
+        */
+       protected function isRootJobOldDuplicate( Job $job ) {
+               global $wgMemc;
+
+               $params = $job->getParams();
+               if ( !isset( $params['rootJobSignature'] ) ) {
+                       return false; // job has no de-deplication info
+               } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
+                       trigger_error( "Cannot check root job; missing 'rootJobTimestamp'." );
+                       return false;
+               }
+
+               // Get the last time this root job was enqueued
+               $timestamp = $wgMemc->get( $this->getRootJobCacheKey( $params['rootJobSignature'] ) );
+
+               // Check if a new root job was started at the location after this one's...
+               return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
+       }
+
        /**
         * @see JobQueue::doWaitForBackups()
         * @return void
@@ -380,22 +474,22 @@ class JobQueueDB extends JobQueue {
         * @return array
         */
        protected function insertFields( Job $job ) {
-               // Rows that describe the nature of the job
-               $descFields = array(
+               $dbw = $this->getMasterDB();
+               return array(
+                       // Fields that describe the nature of the job
                        'job_cmd'       => $job->getType(),
                        'job_namespace' => $job->getTitle()->getNamespace(),
                        'job_title'     => $job->getTitle()->getDBkey(),
                        'job_params'    => self::makeBlob( $job->getParams() ),
-               );
-               // Additional job metadata
-               $dbw = $this->getMasterDB();
-               $metaFields = array(
+                       // Additional job metadata
                        'job_id'        => $dbw->nextSequenceValue( 'job_job_id_seq' ),
                        'job_timestamp' => $dbw->timestamp(),
-                       'job_sha1'      => wfBaseConvert( sha1( serialize( $descFields ) ), 16, 36, 32 ),
+                       'job_sha1'      => wfBaseConvert(
+                               sha1( serialize( $job->getDeduplicationInfo() ) ),
+                               16, 36, 31
+                       ),
                        'job_random'    => mt_rand( 0, self::MAX_JOB_RANDOM )
                );
-               return ( $descFields + $metaFields );
        }
 
        /**
@@ -406,6 +500,15 @@ class JobQueueDB extends JobQueue {
                return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'isempty' );
        }
 
+       /**
+        * @param string $signature Hash identifier of the root job
+        * @return string
+        */
+       private function getRootJobCacheKey( $signature ) {
+               list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
+               return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
+       }
+
        /**
         * @param $params
         * @return string