- $row = $dbw->selectRow( 'job', '*', // find a random job
- array(
- 'job_cmd' => $this->type,
- 'job_token' => '',
- "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
- __METHOD__
- // Bug 42614: "ORDER BY job_random" causes slowness on mysql for some reason
- );
+ if ( $tinyQueue ) { // queue has <= MAX_OFFSET rows
+ // For small queues, using OFFSET will overshoot and return no rows more often.
+ // Instead, this uses job_random to pick a row (possibly checking both directions).
+ $ineq = $gte ? '>=' : '<=';
+ $dir = $gte ? 'ASC' : 'DESC';
+ $row = $dbw->selectRow( 'job', '*', // find a random job
+ array(
+ 'job_cmd' => $this->type,
+ 'job_token' => '', // unclaimed
+ "job_random {$ineq} {$dbw->addQuotes( $rand )}" ),
+ __METHOD__,
+ array( 'ORDER BY' => "job_random {$dir}" )
+ );
+ if ( !$row && !$invertedDirection ) {
+ $gte = !$gte;
+ $invertedDirection = true;
+ continue; // try the other direction
+ }
+ } else { // table *may* have >= MAX_OFFSET rows
+ // Bug 42614: "ORDER BY job_random" with a job_random inequality causes high CPU
+ // in MySQL if there are many rows for some reason. This uses a small OFFSET
+ // instead of job_random for reducing excess claim retries.
+ $row = $dbw->selectRow( 'job', '*', // find a random job
+ array(
+ 'job_cmd' => $this->type,
+ 'job_token' => '', // unclaimed
+ ),
+ __METHOD__,
+ array( 'OFFSET' => mt_rand( 0, self::MAX_OFFSET ) )
+ );
+ if ( !$row ) {
+ $tinyQueue = true; // we know the queue must have <= MAX_OFFSET rows
+ $wgMemc->set( $this->getCacheKey( 'small' ), 1, 30 );
+ continue; // use job_random
+ }
+ }