RE: How to check if session is a hung thread/session

Hi,

The log you expose doesn’t mean a dead lock! It comes from setting deadlock_timeout parameter. Its value is 1 second by default. When a session waits for a lock more than this threshold then a test to see if we are in a deadlock condition is triggered. It is simply that we are waiting to obtain a lock for longer that the value of deadlock_timeout. Any way it could be interpreted as a performance problem when we are frequently waiting more than 1 sec for a lock…

Regards

Michel SALAIS

De : Edwin UY <edwin(dot)uy(at)gmail(dot)com>
Envoyé : lundi 11 novembre 2024 07:45
À : Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc : David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>; pgsql-admin(at)lists(dot)postgresql(dot)org
Objet : Re: How to check if session is a hung thread/session

Thanks Tom,

OK, I've decided to 'painfully' look at the PostgreSQL RDS logs and it is showing something like below.

There seems to be a locking/deadlock issue of some sort somewhere.

I have checked the other days' log prior to the patching and these appear to be a 'normal' occurrence for this database and it wasn't affecting the application nonetheless.

After the patching, it starts affecting the application. Not sure what else I can check on the Aurora PostgreSQL RDS end. I may request them to restart the app server.

[25751]:LOG: process 25751 still waiting for ShareLock on transaction 114953443 after 1000.054 ms

[25751]:DETAIL: Process holding the lock: 22297. Wait queue: 25751.

[25751]:CONTEXT: while locking tuple (1,17) in relation "[table_name]"

[25751]:STATEMENT: [SQL_STATEMENT] for update
[25751]:LOG: process 25751 acquired ShareLock on transaction 114953443 after 4756.967 ms
[25751]:CONTEXT: while locking tuple (1,17) in relation " [table_name] "

On Mon, Nov 11, 2024 at 5:45 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us <mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us> > wrote:

Edwin UY <edwin(dot)uy(at)gmail(dot)com <mailto:edwin(dot)uy(at)gmail(dot)com> > writes:
> I thought it could be the backend has sent something back to the client but
> it never received it and it just kept on doing the same at some intervals.

Your pg_stat_activity output shows the backend is idle, meaning it's
waiting for a client command. While the session has been around for
days, we can see the last client command was about 47 minutes ago,
from your "now() - pg_stat_activity.query_start AS duration" column.
I see no reason to think there is anything interesting here at all,
except for a client that is sitting doing nothing for long periods.

regards, tom lane