Connecting to PDO / MySQL database over unix-socket throws "a retry" error #22981

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1. wyattoday

   added

   Bug

   Status: Needs Triage

   on Jul 31, 2026
2. wyattoday commented on Aug 1, 2026

   

   wyattoday

   on Aug 1, 2026

   Last edited by wyattoday

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   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.
3. arshidkv12 commented on Aug 1, 2026

   

   arshidkv12

   on Aug 1, 2026

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   Please share the sample code.
4. LamentXU123

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   Extension: pdo_mysql

   Status: Needs Feedback

   and removed

   Status: Needs Triage

   on Aug 3, 2026
5. wyattoday commented on Aug 3, 2026

   

   wyattoday

   on Aug 3, 2026

   Last edited by wyattoday

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   The relevant parts of the code are just a PDO object and a test rig to make high-frequency connections to a MySQL database over a unix-socket. (So, not really a lot of code to show).

   		// this class assumes there's a global const
   		// named "DB_CONFIG" that's in the following form:
   		/*
   
   		const DB_CONFIG = [
   			'dsn' => 'mysql',
   			'unix_socket' => '/location/to/mysql/unix.sock',
   			'username'	=> 'your_user',
   			'password'	=> 'your_pass',
   			'dbname'	=> 'your_db_name'
   		];
   		*/
   
   		if (isset(DB_CONFIG['unix_socket']))
   			$connect_str = DB_CONFIG['dsn'].':unix_socket='.DB_CONFIG['unix_socket'];
   		else
   			$connect_str = DB_CONFIG['dsn'].':host='.DB_CONFIG['host'].';port='.DB_CONFIG['port'];
   
   		self::$_instance = new PDO($connect_str.';dbname='.DB_CONFIG['dbname'],
   			DB_CONFIG['username'],
   			DB_CONFIG['password'],
   			[
   				PDO::ATTR_EMULATE_PREPARES => false,
   				PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
   				PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
   				Pdo\Mysql::ATTR_USE_BUFFERED_QUERY => false
   			]
   		);
   

   Then just use that connection to make a query of some sort (it doesn't really matter what you do).

   As I said above "persistent connections" (PDO::ATTR_PERSISTENT => true) works-around this problem (but has it's own trade-offs such that we need to tread carefully). Also, digging into the the mysqlnd / php-poll code I see that the "2002" error code is a try-again condition that is handled incorrectly (it's handled as an error rather than a wait-try-again loop condition).

   Also, there's a chance for better resource management. That is, a step between "persistent connections" and not. Namely the unix-socket itself can be a resource that is "opened" and maintained across the lifetime of the php / php-fpm process and new database connections can be made over that shared resource. So the "state" problems / bugs of persistent connections can be avoided by treating the "tunnel" as a cached-resource and the connections are all fresh with their own state.

   But that's just a suggestion for better/faster resource management in mysqlnd. The actual bug is not handling the "2002" error code correctly in mysqlnd.
6. github-actions

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   Status: Needs Triage

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   Status: Needs Feedback

   on Aug 3, 2026