Possible DB Deadlock Situation

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Gambid
Registered User
Posts: 15
Joined: Fri Jul 22, 2011 10:35 am

Possible DB Deadlock Situation

Post by Gambid »

Hi everyone,

for a little while now (not sure if it started after the 3.3.10 update) I noticed moments where my website is simply not loading for several minutes. It took me a while to realize that it comes from the database and what I suspect is a deadlock situation. This makes it of course difficult to track down as you need to be present when it happens. So a moment ago the problem occurred again and I rushed to the phpmyadmin to have a look at the db (mariadb). Unfortunately not a lot can be seen.
Screenshot 2023-03-08 212231.jpg
Any tips on how to better get to the bottom of this. I tried killing the processes in the hope to resolve the deadlock but ended up restarting the service altogether. If I leave it, the situation will resolve on its own, guess maria will recognize the deadlock at some point and kill the processes itself.

I was hoping to see the statements but unfortunately no luck.

Thanks in advance!
jeffythedragonslayer
Registered User
Posts: 24
Joined: Fri Mar 03, 2023 2:14 am

Re: Possible DB Deadlock Situation

Post by jeffythedragonslayer »

When a process goes rouge like this I typically attach strace to it and then lookup what the system calls its making do to try to understand if it is stuck.
Gambid
Registered User
Posts: 15
Joined: Fri Jul 22, 2011 10:35 am

Re: Possible DB Deadlock Situation

Post by Gambid »

A little update, which I hope may help others that run into a similar situation.

Nothing is 100% certain but the problem may have been caused by a simple overload and a pm.max_children configuration that simply no longer can handle the traffic of the website. I am running the website with PHP-FPM and still had the default value, which in my case was 10 and has been maxed out almost all the time. Ever since the value was increased the problem has not occurred once and all the warnings regarding to the max_children being reached have disappeared.

Hope this helps :)
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