MySQL server has gone away

One day I suddenly got the ”MySQL server has gone away” error message in my web-application. No queries were running. The webpage (cron update) that generates the error is a heavy one with approx. 10 000 queries. I had never seen this error message before and the solutions to fix it seems to be different in each case. The way I solved the error was the following.

1) I ran ”mysqlcheck” in repair mode and it fixed problems with clients that were using or hadn’t closed tables properly.

2) I found this workaround.

3) Then I checked the mysql servers system variable wait_timeout with:
mysqladmin -u username -p variables

The value was 10 which were pretty low considering the default value which is 28800.

wait_timeout is the number of seconds the server waits for activity on a noninteractive connection before closing it. This timeout applies only to TCP/IP and Unix socket file connections, not to connections made using named pipes, or shared memory.

4) I searched and found the ”wait_timeout” value in the mysql config file /etc/my.cnf. I had set this value to 10 when I did some mysql performance optimization in the past. Then I raised this value to a higher number.

5) Restarted mysql and ran the webpage. Everything worked fine.

I still don’t know why this error occured that day. The server configuration worked good before the accident and I haven’t made any changes lately. Very strange!

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