Using multiple transactions in PHP with PDO leads to unexpected deadlocks
I'm sure I'm missing something obvious here, but I'm experiencing issues with deadlocks when trying to execute multiple transactions using PDO in PHP 8.1... My application involves a series of balance updates across different user accounts, and I orchestrate them using transactions for data integrity. However, I occasionally encounter a `SQLSTATE[40001]: Serialization failure: 1213 Deadlock found when trying to get lock; try restarting transaction` behavior. Here’s a simplified version of my code: ```php try { $pdo->beginTransaction(); // Update balance for User A $stmt = $pdo->prepare('UPDATE accounts SET balance = balance - ? WHERE id = ?'); $stmt->execute([$amountA, $userAId]); // Update balance for User B $stmt = $pdo->prepare('UPDATE accounts SET balance = balance + ? WHERE id = ?'); $stmt->execute([$amountA, $userBId]); $pdo->commit(); } catch (PDOException $e) { if ($e->getCode() === '40001') { // Handle deadlock $pdo->rollBack(); echo 'Deadlock occurred. Please try again.'; } else { // Handle other exceptions $pdo->rollBack(); echo 'behavior: ' . $e->getMessage(); } } ``` I’ve tried implementing a retry mechanism for the transaction, but I still face deadlocks intermittently. After some research, I learned that deadlocks can occur due to the order in which locks are acquired, especially when multiple transactions are involved. In this specific case, I suspect that concurrent updates to the same accounts from different processes may be causing the deadlocks. I also checked the isolation level of my transactions, which is set to `REPEATABLE READ`. I wonder if switching to `READ COMMITTED` would help or if there are better strategies to avoid these deadlocks altogether. Any insights on best practices for managing transactions in this context would be greatly appreciated. Any help would be greatly appreciated! I'm working on a application that needs to handle this. Any ideas what could be causing this? The stack includes Php and several other technologies. Any examples would be super helpful.