Laravel Question posted in
The official Laravel Documentation can be found here.

How to handle deadlocks in Laravel

Laravel docs recommends using attempts to deal with Deadlocks (https://shorturl.at/bsKta)

But, the handleTransactionException() method inside the transaction() method has a comment:

On a deadlock, MySQL rolls back the entire transaction so we can’t just retry the query. We have to throw this exception all the way out and let the developer handle it in another way. We will decrement too.

Does it mean to handle Deadlocks I should wrap the DB::transaction() with a try/catch? What’s the use of attempts then in this case?

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2

Answers


  1. 0

    As mentioned in the Larave Doc, attempts means:

    Specifies the number of times a transaction should be retried when a deadlock occurs.

    But about using try/catch, I can say that when MySQL reaches a deadlock, it will throw an exception. try/catch allows you to do something with an Exception. For e.g:

    try {
    DB::transaction(function () {
        // Your transaction logic
    }, 5); // Laravel will attempt the transaction up to 5 times
} catch (Exception $e) {
    // Handle the error after all attempts fail
    // For example, you can log the error or show a message to the user
    Log::warning($e->getMessage());
}
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  2. 0

    Yes, you should wrap DB::transaction() in a try/catch block to handle deadlocks. Although Laravel’s attempts parameter allows retries for some errors, deadlocks are special because MySQL rolls back the entire transaction. Therefore, Laravel can’t automatically retry it, and you need to handle deadlocks manually.

    Here’s a simple approach:

    1. Wrap your transaction in a try/catch.
    2. Check for deadlock error codes (1213 or 40001).
    3. Retry the transaction a few times if a deadlock occurs.

    Example code:

    use IlluminateSupportFacadesDB;
use Exception;

$attempts = 5;

for ($i = 0; $i < $attempts; $i++) {
    try {
        DB::transaction(function () {
            // Your transactional code
        });
        break; // Success, exit the loop
    } catch (Exception $e) {
        if ($e->getCode() == 1213 || $e->getCode() == 40001) { // Deadlock codes
            if ($i === $attempts - 1) {
                throw $e; // Last attempt, throw error
            }
        } else {
            throw $e; // Non-deadlock errors
            Log::warning($e->getMessage());
        }
    }
}

    This way, you manually retry the transaction on deadlocks.

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