How to debug "Aborted connection (unknown error)" ?

[Florent B]

Hi everyone,

On a 3-nodes Galera cluster, I often have errors like :

[Warning] Aborted connection 423337 to db: 'my_db' user: 'my_user' host:
'user_host' (Unknown error)

I don't know what could be the problem, how can I do to debug this ?

Thank you.

Florent

[Johan Wikström]

Hi,

I have this problem too. Fresh install of three Debian 8, MariaDB 10.1.7. Quite often the JBosses connecting to either of the three galera servers loses connection, and I get the error above.

No network problems that I can see, all machines on the same subnet, including the old MySQL server that I used before and where i never experienced any connectivity issues.

Thanks

Johan

[alexey.y...@galeracluster.com]

Check effective OS limits on mysqld process, specifically open files. It
should be a very big number.

[Johan Wikström]

Thank you!

I thought this was a nobrainer, having set high values in limits.conf. But Google has now taught me that this was far from the whole story.

I needed to edit /etc/systemd/system/mysql.service

and add

LimitNOFILE=infinity

Checking with

 cat /proc/$(pgrep mysqld$)/limits

and

MariaDB [(none)]> show global variables like 'open%';

now gives me 65535 instead of the previous 1024. I thought this was a bit hard to find, usually applications are quite verbose when hitting the max number of open files roof.

I must have missed this part in the installation instructions. 

Thank you Alexey!

Best regards,

Johan

[Johan Wikström]

Edit: The problems still exist, even efter raising the max number of open files.

[Florent B]

Hi,

It does not seem to be the problem here.
I have 2505 in open_files_limit & proc limits (I don't know why 2505...)
and only 200-300 opened files on each node (lsof).

[alexey.y...@galeracluster.com]

On 2015-11-03 10:02, Florent B wrote:
> Hi,
>
> It does not seem to be the problem here.
> I have 2505 in open_files_limit & proc limits (I don't know why
> 2505...)
> and only 200-300 opened files on each node (lsof).

It appears that some other resources (like threads) contribute to that
count. Experience shows that 2505 is a rather low value. But it it not
to say that the problem may not lie elsewhere. It is one possible cause
and it makes sense to eliminate it.

[Florent B]

On 11/03/2015 09:40 PM, alexey.y...@galeracluster.com wrote:
>
> It appears that some other resources (like threads) contribute to that
> count. Experience shows that 2505 is a rather low value. But it it not
> to say that the problem may not lie elsewhere. It is one possible
> cause and it makes sense to eliminate it.
>

Ok I will try it then.

But why my setup of MariaDB/Galera didn't create systemd service files ?
(/usr/lib/systemd/system/mysqld.service &
/etc/systemd/system/mysql.service does not exist).

I'm on Jessie, package version 10.0.22+maria-1~jessie.