PDO connection timed out in API, php-fpm restart solves it - php

Question

I keep getting the following error from my code:
Database connect failed: PDO::__construct(): send of 12 bytes failed with errno=110 Connection timed out
This error persistently happens on an api. If that api keeps getting called a lot during the day this does not happen. Only when the api is not used for some time.
I can solve this by doing a php-fpm restart/reload, but this shouldn't be the solution.
Does anybody have any idea how to solve this?
--EDIT--
This is the code for connection to the database:
public function connectDatabase($allow_persistent = true)
{
$this->db = null;
$this->readINI();
$pdo_attr = [
PDO::ATTR_PERSISTENT => $allow_persistent,
PDO::MYSQL_ATTR_INIT_COMMAND => "SET CHARACTER SET utf8;",
PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true,
];
$this->db = new PDO("mysql:host=" . $this->db_data_dbhost . ";dbname=" . $this->db_data_dbname . ";charset=utf8", $this->db_data_username, $this->db_data_password, $pdo_attr);
$this->db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
To itterate some more, this is used on two API's at the moment.
One is consistently used by customers and never encounters this problem
The second is not used by a lot of customers yet seeing as this is still in development, it's only with a few customers for testing purposes. We do try to push an app to the appstore but it gets shot down by this problem. This API will eventually run into the error as depicted above and will not recover from this state without restarting/reloading the php-fpm service.

Answer 1

Using persistant connections is not that good (see why), but still, to solve this you may want to increase MySQL connections timeout.
To achieve this, see wait_timeout parameter for my.ini.
p.s. Also, you can catch this error and just reconnect to the database.

Answer 2

After much testing and research we found this bug was causing the issue:
https://bugs.php.net/bug.php?id=64549
Our solution was to use the error control operator '#' on the PDO connect:
$connection = #new PDO(
$connection_type.":dbname=".$dbname.";host=".$host,
$username,
$password,
[
PDO::ATTR_PERSISTENT => TRUE,
PDO::ATTR_TIMEOUT => 15,
PDO::MYSQL_ATTR_INIT_COMMAND => "SET sql_mode='POSTGRESQL'"
]
);
If you are using your own error handler set_error_handler() you will need to ignore if error_reporting() level === 0.
// This handles the mysqlnd persistent connections bug when the # symbol is used it and the error is suppressed
if ( 0 !== error_reporting() ) {
// Do your regular customer error handling here
}else{
// ignore this since it is throwing a false positive from the persistent connection bug
}
I hope this saves someone hours troubleshooting. I hope the people behind PHP figure out a solution for this bug. It has annoyed many people for years.