intermittent MySQL server has gone away error

Question

I have been scratching my head trying to figure out what is causing an intermittent error in my script. The error is: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away.

My script below is part of a function that does a curl, gets some values from a JSON response, and then writes them to a table. I'd say 80% of the time it works fine and then the other 20% i get the server gone away error. I haven't been able to identify any trends that causes it to error out, it just seems to be random. Any ideas why i might be getting this error? thanks for checking this out

    ...
    //post via cURL 
    $ch = curl_init( $url );
    $timeout = 500;
    curl_setopt( $ch, CURLOPT_POST, 1);
    curl_setopt( $ch, CURLOPT_POSTFIELDS, $myvars);
    curl_setopt( $ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt( $ch, CURLOPT_CONNECTTIMEOUT, $timeout);
    curl_setopt( $ch, CURLOPT_HEADER, 0);
    curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1);
    $this->response = curl_exec( $ch );
    $this->json_decoded = json_decode($this->response);
    $this->full = print_r($this->json_decoded, true);
    $client_leadid = $this->json_decoded->Parameters->lead_id;
    $client_status = $this->json_decoded->Status;   
    $length = curl_getinfo($ch);
    curl_close($ch);

    //record in DB
    $insert = $this->full.' | '.$url.' | '.$myvars.' | '.$this->date . ' | Time Taken: '.$length['total_time'];
    $db->exec("UPDATE table SET client_resp = '$insert' WHERE global_id = '$this->leadid' LIMIT 1");
    $db->exec("UPDATE table SET client_leadid = '$client_leadid' WHERE global_id = '$this->leadid' LIMIT 1");

Answer 1

This is probably happening because your CURL request is taking longer then the mysql connection timeout

either 1) set a request-timeout for CURL so it dies sooner on errors (CURLOPT_CONNECTTIMEOUT is only for connections- CURLOPT_TIMEOUT is for the overall length of the request and it will stop if the server doesn't respond in time) 2) turn up the mysql idle timeouts to prevent the server from disconnecting you for not sending queries
3) detect the error and automatically reconnect to mysql

mysql> show variables like "%timeout%";
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| connect_timeout          | 5     |
| delayed_insert_timeout   | 300   |
| innodb_lock_wait_timeout | 50    |
| interactive_timeout      | 28800 |
| net_read_timeout         | 30    |
| net_write_timeout        | 60    |
| slave_net_timeout        | 3600  |
| table_lock_wait_timeout  | 50    |
| wait_timeout             | 28800 |
+--------------------------+-------+
9 rows in set (0.00 sec)

wait_timeout and interactive_timeout are the two you care about