Fix backport

Signed-off-by: Git'Fellow <12234510+solracsf@users.noreply.github.com>

apps/files_sharing/lib/DeleteOrphanedSharesJob.php

@@ -30,6 +30,11 @@ namespace OCA\Files_Sharing;
 use OCP\AppFramework\Db\TTransactional;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\BackgroundJob\TimedJob;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+use PDO;
+use Psr\Log\LoggerInterface;
+use function array_map;
 
 /**
  * Delete all share entries that have no matching entries in the file cache table.
@@ -69,15 +74,45 @@ class DeleteOrphanedSharesJob extends TimedJob {
 	 * @param array $argument unused argument
 	 */
 	public function run($argument) {
-		$connection = \OC::$server->getDatabaseConnection();
-		$logger = \OC::$server->getLogger();
+		$qbSelect = $this->db->getQueryBuilder();
+		$qbSelect->select('id')
+			->from('share', 's')
+			->leftJoin('s', 'filecache', 'fc', $qbSelect->expr()->eq('s.file_source', 'fc.fileid'))
+			->where($qbSelect->expr()->isNull('fc.fileid'))
+			->setMaxResults(self::CHUNK_SIZE);
+		$deleteQb = $this->db->getQueryBuilder();
+		$deleteQb->delete('share')
+			->where(
+				$deleteQb->expr()->in('id', $deleteQb->createParameter('ids'), IQueryBuilder::PARAM_INT_ARRAY)
+			);
 
-		$sql =
-			'DELETE FROM `*PREFIX*share` ' .
-			'WHERE `item_type` in (\'file\', \'folder\') ' .
-			'AND NOT EXISTS (SELECT `fileid` FROM `*PREFIX*filecache` WHERE `file_source` = `fileid`)';
-
-		$deletedEntries = $connection->executeUpdate($sql);
-		$logger->debug("$deletedEntries orphaned share(s) deleted", ['app' => 'DeleteOrphanedSharesJob']);
+		/**
+		 * Read a chunk of orphan rows and delete them. Continue as long as the
+		 * chunk is filled and time before the next cron run does not run out.
+		 *
+		 * Note: With isolation level READ COMMITTED, the database will allow
+		 * other transactions to delete rows between our SELECT and DELETE. In
+		 * that (unlikely) case, our DELETE will have fewer affected rows than
+		 * IDs passed for the WHERE IN. If this happens while processing a full
+		 * chunk, the logic below will stop prematurely.
+		 * Note: The queries below are optimized for low database locking. They
+		 * could be combined into one single DELETE with join or sub query, but
+		 * that has shown to (dead)lock often.
+		 */
+		$cutOff = $this->time->getTime() + self::INTERVAL;
+		do {
+			$deleted = $this->atomic(function () use ($qbSelect, $deleteQb) {
+				$result = $qbSelect->executeQuery();
+				$ids = array_map('intval', $result->fetchAll(PDO::FETCH_COLUMN));
+				$result->closeCursor();
+				$deleteQb->setParameter('ids', $ids, IQueryBuilder::PARAM_INT_ARRAY);
+				$deleted = $deleteQb->executeStatement();
+				$this->logger->debug("{deleted} orphaned share(s) deleted", [
+					'app' => 'DeleteOrphanedSharesJob',
+					'deleted' => $deleted,
+				]);
+				return $deleted;
+			}, $this->db);
+		} while ($deleted >= self::CHUNK_SIZE && $this->time->getTime() <= $cutOff);
 	}
 }