feat(files)): Add retry logic to cover deadlock situations when moving many files

Signed-off-by: Louis Chemineau <louis@chmn.me>

lib/private/Files/Cache/Cache.php

@@ -40,6 +40,7 @@
 
 namespace OC\Files\Cache;
 
+use Doctrine\DBAL\Exception\RetryableException;
 use Doctrine\DBAL\Exception\UniqueConstraintViolationException;
 use OC\Files\Search\SearchComparison;
 use OC\Files\Search\SearchQuery;
@@ -692,7 +693,6 @@ class Cache implements ICache {
 				throw new \Exception('Invalid target storage id: ' . $targetStorageId);
 			}
 
-			$this->connection->beginTransaction();
 			if ($sourceData['mimetype'] === 'httpd/unix-directory') {
 				//update all child entries
 				$sourceLength = mb_strlen($sourcePath);
@@ -715,12 +715,31 @@ class Cache implements ICache {
 					$query->set('encrypted', $query->createNamedParameter(0, IQueryBuilder::PARAM_INT));
 				}
 
-				try {
-					$query->execute();
-				} catch (\OC\DatabaseException $e) {
-					$this->connection->rollBack();
-					throw $e;
+				// Retry transaction in case of RetryableException like deadlocks.
+				// Retry up to 4 times because we should receive up to 4 concurrent requests from the frontend
+				$retryLimit = 4;
+				for ($i = 1; $i <= $retryLimit; $i++) {
+					try {
+						$this->connection->beginTransaction();
+						$query->executeStatement();
+						break;
+					} catch (\OC\DatabaseException $e) {
+						$this->connection->rollBack();
+						throw $e;
+					} catch (RetryableException $e) {
+						// Simply throw if we already retried 4 times.
+						if ($i === $retryLimit) {
+							throw $e;
+						}
+
+						$this->connection->rollBack();
+
+						// Sleep a bit to give some time to the other transaction to finish.
+						usleep(100 * 1000 * $i);
+					}
 				}
+			} else {
+				$this->connection->beginTransaction();
 			}
 
 			$query = $this->getQueryBuilder();