* Class to handle job queues stored in the DB
*
* @ingroup JobQueue
- * @since 1.20
+ * @since 1.21
*/
class JobQueueDB extends JobQueue {
- const CACHE_TTL = 30; // integer; seconds
- const MAX_JOB_RANDOM = 2147483647; // 2^31 - 1; used for job_random
+ const CACHE_TTL = 300; // integer; seconds to cache queue information
+ const MAX_AGE_PRUNE = 604800; // integer; seconds a job can live once claimed
+ const MAX_ATTEMPTS = 3; // integer; number of times to try a job
+ const MAX_JOB_RANDOM = 2147483647; // integer; 2^31 - 1, used for job_random
/**
* @see JobQueue::doIsEmpty()
$dbw->setFlag( $autoTrx ? DBO_TRX : 0 ); // restore automatic begin()
}
- $wgMemc->set( $key, 'false', $ttl );
+ $wgMemc->set( $key, 'false', $ttl ); // queue is not empty
} );
}
protected function doPop() {
global $wgMemc;
- $uuid = wfRandomString( 32 ); // pop attempt
+ if ( $wgMemc->get( $this->getEmptinessCacheKey() ) === 'true' ) {
+ return false; // queue is empty
+ }
$dbw = $this->getMasterDB();
$dbw->commit( __METHOD__, 'flush' ); // flush existing transaction
+ $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
- $row = false; // row claimed
- $rand = mt_rand( 0, self::MAX_JOB_RANDOM ); // encourage concurrent UPDATEs
- $gte = (bool)mt_rand( 0, 1 ); // find rows with rand before/after $rand
- // Try to reserve a DB row...
- if ( $this->claim( $uuid, $rand, $gte ) || $this->claim( $uuid, $rand, !$gte ) ) {
- // Fetch any row that we just reserved...
- $row = $dbw->selectRow( 'job', '*',
- array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__ );
- // Check if another process deleted it as a duplicate
- if ( !$row ) {
- wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
- continue; // try again
- }
- // 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
+ // 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 );
}
- $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( $row->job_id )}" ),
- __METHOD__
- );
- }
- } else {
+ }
+ // Check if we found a row to reserve...
+ if ( !$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 );
/**
* Reserve a row with a single UPDATE without holding row locks over RTTs...
+ *
* @param $uuid string 32 char hex string
* @param $rand integer Random unsigned integer (31 bits)
* @param $gte bool Search for job_random >= $random (otherwise job_random <= $random)
- * @return integer Number of affected rows
+ * @return Row|false
*/
- protected function claim( $uuid, $rand, $gte ) {
+ protected function claimRandom( $uuid, $rand, $gte ) {
$dbw = $this->getMasterDB();
$dir = $gte ? 'ASC' : 'DESC';
$ineq = $gte ? '>=' : '<=';
- if ( $dbw->getType() === 'mysql' ) {
- // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
- // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
- // Oracle and Postgre have no such limitation. However, MySQL offers an
- // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
- // The DB wrapper functions do not support this, so it's done manually.
- $dbw->query( "UPDATE {$dbw->tableName( 'job' )}
- SET
- job_token = {$dbw->addQuotes( $uuid ) },
- job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}
- WHERE (
- job_cmd = {$dbw->addQuotes( $this->type )}
- AND job_token = {$dbw->addQuotes( '' )}
- AND job_random {$ineq} {$dbw->addQuotes( $rand )}
- ) ORDER BY job_random {$dir} LIMIT 1",
- __METHOD__
+
+ $row = false; // the row acquired
+ // This uses a replication safe method for acquiring jobs. One could use UPDATE+LIMIT
+ // instead, but that either uses ORDER BY (in which case it deadlocks in MySQL) or is
+ // not replication safe. Due to http://bugs.mysql.com/bug.php?id=6980, subqueries cannot
+ // be used here with MySQL.
+ do {
+ $row = $dbw->selectRow( 'job', '*', // find a random job
+ array(
+ 'job_cmd' => $this->type,
+ 'job_token' => '',
+ "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
+ __METHOD__,
+ array( 'ORDER BY' => "job_random {$dir}" )
);
- } else {
- // Use a subquery to find the job, within an UPDATE to claim it.
- // This uses as much of the DB wrapper functions as possible.
+ if ( $row ) { // claim the job
+ $dbw->update( 'job', // update by PK
+ array(
+ 'job_token' => $uuid,
+ 'job_token_timestamp' => $dbw->timestamp(),
+ 'job_attempts = job_attempts+1' ),
+ array( 'job_cmd' => $this->type, 'job_id' => $row->job_id, 'job_token' => '' ),
+ __METHOD__
+ );
+ // This might get raced out by another runner when claiming the previously
+ // selected row. The use of job_random should minimize this problem, however.
+ if ( !$dbw->affectedRows() ) {
+ $row = false; // raced out
+ }
+ } else {
+ break; // nothing to do
+ }
+ } while ( !$row );
+
+ return $row;
+ }
+
+ /**
+ * Reserve a row with a single UPDATE without holding row locks over RTTs...
+ *
+ * @param $uuid string 32 char hex string
+ * @return Row|false
+ */
+ protected function claimOldest( $uuid ) {
+ $dbw = $this->getMasterDB();
+
+ $row = false; // the row acquired
+ do {
+ if ( $dbw->getType() === 'mysql' ) {
+ // Per http://bugs.mysql.com/bug.php?id=6980, we can't use subqueries on the
+ // same table being changed in an UPDATE query in MySQL (gives Error: 1093).
+ // Oracle and Postgre have no such limitation. However, MySQL offers an
+ // alternative here by supporting ORDER BY + LIMIT for UPDATE queries.
+ $dbw->query( "UPDATE {$dbw->tableName( 'job' )} " .
+ "SET " .
+ "job_token = {$dbw->addQuotes( $uuid ) }, " .
+ "job_token_timestamp = {$dbw->addQuotes( $dbw->timestamp() )}, " .
+ "job_attempts = job_attempts+1 " .
+ "WHERE ( " .
+ "job_cmd = {$dbw->addQuotes( $this->type )} " .
+ "AND job_token = {$dbw->addQuotes( '' )} " .
+ ") ORDER BY job_id ASC LIMIT 1",
+ __METHOD__
+ );
+ } else {
+ // Use a subquery to find the job, within an UPDATE to claim it.
+ // This uses as much of the DB wrapper functions as possible.
+ $dbw->update( 'job',
+ array(
+ 'job_token' => $uuid,
+ 'job_token_timestamp' => $dbw->timestamp(),
+ 'job_attempts = job_attempts+1' ),
+ array( 'job_id = (' .
+ $dbw->selectSQLText( 'job', 'job_id',
+ array( 'job_cmd' => $this->type, 'job_token' => '' ),
+ __METHOD__,
+ array( 'ORDER BY' => 'job_id ASC', 'LIMIT' => 1 ) ) .
+ ')'
+ ),
+ __METHOD__
+ );
+ }
+ // Fetch any row that we just reserved...
+ if ( $dbw->affectedRows() ) {
+ $row = $dbw->selectRow( 'job', '*',
+ array( 'job_cmd' => $this->type, 'job_token' => $uuid ), __METHOD__
+ );
+ if ( !$row ) { // raced out by duplicate job removal
+ wfDebugLog( 'JobQueueDB', "Row deleted as duplicate by another process." );
+ }
+ } else {
+ break; // nothing to do
+ }
+ } while ( !$row );
+
+ return $row;
+ }
+
+ /**
+ * Recycle or destroy any jobs that have been claimed for too long
+ *
+ * @return integer Number of jobs recycled/deleted
+ */
+ protected function recycleStaleJobs() {
+ $now = time();
+ $dbw = $this->getMasterDB();
+ $count = 0; // affected rows
+
+ if ( $this->claimTTL > 0 ) { // re-try stale jobs...
+ $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' => $uuid, 'job_token_timestamp' => $dbw->timestamp() ),
- array( 'job_id = (' .
- $dbw->selectSQLText( 'job', 'job_id',
- array(
- 'job_cmd' => $this->type,
- 'job_token' => '',
- "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
- __METHOD__,
- array( 'ORDER BY' => "job_random {$dir}", 'LIMIT' => 1 ) ) .
- ')'
- ),
+ array(
+ 'job_token' => '',
+ 'job_token_timestamp' => $dbw->timestamp( $now ) ), // time of release
+ 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 )}" ),
__METHOD__
);
+ $count += $dbw->affectedRows();
}
- return $dbw->affectedRows();
+
+ // Just destroy stale jobs...
+ $pruneCutoff = $dbw->timestamp( $now - self::MAX_AGE_PRUNE );
+ $conds = array(
+ 'job_cmd' => $this->type,
+ "job_token != {$dbw->addQuotes( '' )}", // was acquired
+ "job_token_timestamp < {$dbw->addQuotes( $pruneCutoff )}" // stale
+ );
+ 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();
+
+ return $count;
}
/**
*/
protected function doAck( Job $job ) {
$dbw = $this->getMasterDB();
- if ( $dbw->trxLevel() ) {
- wfWarn( "Attempted to ack a job in a transaction; committing first." );
- $dbw->commit(); // push existing transaction
- }
+ $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
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