Re: MySQL server has gone away

On 4/3/2017 8:15 AM, Mahmood N wrote:
> When I click on the submit button in Moodle and it is waiting for refresh, I execute the mysql command but the output is not meaningful
>
> mahmood@ce:/var/www/html/courses$ mysql -u moodle -p
> Enter password:
> Welcome to the MySQL monitor.  Commands end with ; or \g.
> Your MySQL connection id is 30912
> Server version: 5.5.54-0ubuntu0.14.04.1 (Ubuntu)
>
> Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
>
> Oracle is a registered trademark of Oracle Corporation and/or its
> affiliates. Other names may be trademarks of their respective
> owners.
>
> Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
>
> mysql> show full processlist
>      ->
>      ->
>
>
>
> Meanwhile using Webmin, I execute the same command for that user and see
>   Output from SQL command show full processlist ..
> | Id | User | Host | db | Command | Time | State | Info |
> | 30912 | moodle | localhost |
>   | Sleep | 42 |
>
>
>
> I am not expert with MySQL, however as the Moodle admin I am trying to fix the problems.
> Regards,
> Mahmood
>

You need to consider a few possibilities,

a) Moodle didn't want to wait long enough for the query to complete (a 
Moodle Timeout) so it said "the server is not responding..."

b) Moodle sent MySQL a command that was "too large".  To protect itself 
from abuse, all MySQL instances have a configurable limit about how 
"large" a command can be. If the command is larger than this limit, the 
server rejects it and closes the connection.  (this could explain why 
the query you just attempted from Moodle is not visible in the list of 
executing commands)

c) Something is unstable in your MySQL instance. The MySQL Error Log may 
contain details explaining why mysqld was unable to stay running.  The 
angel process mysqld_safe would try to restart the server automatically 
which could explain why Moodle was only unresponsive for a short while.

Additional resources:
https://dev.mysql.com/doc/refman/5.6/en/problems.html   (in particular, 
review B.5.2)

-- 
Shawn Green
MySQL Senior Principal Technical Support Engineer
Oracle USA, Inc. - Integrated Cloud Applications & Platform Services
Office: Blountville, TN

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