Connecting to PDO / MySQL database over unix-socket throws "a retry" error

[wyattoday]

Description

The following code:

<?php

Resulted in this output:

Error message: SQLSTATE[HY000] [2002] Resource temporarily unavailable

Error stack trace:

#0 /location-to-php.php(43): PDO->__construct()
#xx: our code

But I expected this output instead:

No crash.

This is a bug in mysqlnd in that it returns a "2002" error code (I looked into the code -- it's a "try again" code, that is a look / backoff should be taken). This happens when connecting to MySQL using a unix socket. And it happens when a high-frequency of calls are made in short succession.

Ideally a unix-socket should be opened once per process and all communication should happen on that socket (rather than opening and closing it over and over again). And "retry" "errors" (not an error) should be handled correctly.

I haven't dug into the mysqlnd extension into how to fix this yet. If someone wants to jump on this first, that would be appreciated. Otherwise I'll dig into it next week.

PHP Version

8.5.9

Operating System

Debian 12

[wyattoday]

Using PDO::ATTR_PERSISTENT => true does workaround this issue (but, we've been wary of using it in the past due to issues we've had in the past).

Either way, this is a bug in mysqlnd that's worth digging into and fixing (in my opinion). And if we find subsequent issues with persistent connections we'll report them and dig into them.