IndexerJob: Check enough running jobs probabilistically

Signed-off-by: Marcel Klehr <mklehr@gmx.net>

Author: marcelklehr

lib/BackgroundJobs/IndexerJob.php

@@ -145,8 +145,6 @@ protected function getMaxIndexingTime(): int {
 	}
 
 	protected function hasEnoughRunningJobs(): bool {
-		// Sleep a bit randomly to avoid a scenario where all jobs are started at the same time and kill themselves directly
-		sleep(rand(1, 30));
 		if (!$this->jobList->hasReservedJob(static::class)) {
 			// short circuit to false if no jobs are running, yet
 			return false;
@@ -157,7 +155,8 @@ protected function hasEnoughRunningJobs(): bool {
 			$query = $this->db->getQueryBuilder();
 			$query->select('*')
 				->from('jobs')
-				->where($query->expr()->gt('reserved_at', $query->createNamedParameter($this->timeFactory->getTime() - 6 * 3600, IQueryBuilder::PARAM_INT)))
+				->where($query->expr()->gt('reserved_at', $query->createNamedParameter($this->timeFactory->getTime() - $this->getMaxIndexingTime(), IQueryBuilder::PARAM_INT)))
+				->where($query->expr()->gte('last_run', 'reserved_at')
 				->andWhere($query->expr()->eq('id', $query->createNamedParameter($job->getId(), IQueryBuilder::PARAM_INT)))
 				->setMaxResults(1);
 
@@ -172,7 +171,10 @@ protected function hasEnoughRunningJobs(): bool {
 				$this->logger->warning('Querying reserved jobs failed', ['exception' => $e]);
 			}
 		}
-		return $count >= $this->appConfig->getAppValueInt('indexing_max_jobs_count', self::DEFAULT_MAX_JOBS_COUNT);
+		$maxCount = $this->appConfig->getAppValueInt('indexing_max_jobs_count', self::DEFAULT_MAX_JOBS_COUNT);
+		// Either there are already less than the maximum, or we roll the dice according to the proportion of allowed jobs vs currently running ones
+		// e.g. assume 8 jobs are allowed, currently there are 10 running, then we roll the dice and want to be lower than 0.8
+		return $count <= $maxCount || $maxCount / $count > rand(0, 10000) / 10000);
 	}
 
 	/**