Postgres Pro
Downloads
Home   >   mailing lists

Re: Performance bottleneck. High active sessions but postmaster kernel threads are in a sleep state, low CPU utilization - Mailing list pgsql-admin

From Hotmail
Subject Re: Performance bottleneck. High active sessions but postmaster kernel threads are in a sleep state, low CPU utilization
Date
Msg-id BYAPR06MB4023DF70385EC0C8E3E50C63D77C9@BYAPR06MB4023.namprd06.prod.outlook.com
Whole thread Raw
In response to Re: Performance bottleneck. High active sessions but postmaster kernel threads are in a sleep state, low CPU utilization  (Hotmail <crajac66@hotmail.com>)
Responses Re: Performance bottleneck. High active sessions but postmaster kernel threads are in a sleep state, low CPU utilization
List pgsql-admin
Tree view
We actually keep track of the wait events in another grafana graph. We use the following query to generate the graph. (We assume that an active session that has a NULL wait_event is "ON CPU”.  Not sure if our assuming an active session with a null wait being on cpu is valid. We sample pg_stat_activity every 30 seconds. 

SELECT
 coalesce(wait_event, 'ON CPU') AS type,
 count(*)
FROM
 pg_stat_activity
WHERE
 state = 'active'
 AND usename != 'repmgr'
GROUP BY
 TYPE
ORDER BY
 count(*) DESC ";

Here’s a sample from our wait_event graph during times when we see high active sessions but a sleeping postgres OS process. Is it possible we could be hitting an un-instremented wait event?




Craig
On Mar 31, 2021, 10:00 AM -0600, Hotmail <crajac66@hotmail.com>, wrote:
Unfortunately, the wait_event and wait_event_type columns are all NULL for these active sessions. 

Craig
On Mar 31, 2021, 3:47 AM -0600, Laurenz Albe <laurenz.albe@cybertec.at>, wrote:
On Tue, 2021-03-30 at 12:22 -0600, Hotmail wrote:
We are trying to gain some insight into a performance bottleneck that we are hitting while load testing Postgres on 11.11.
[hundreds of active sessions, but CPU is not maxed out]

With that many active sessions you are probably hitting some contention inside
the database. Look at "wait_event" and "wait_event_type" in pg_stat_activity.

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com

Attachment

pgsql-admin by date:

Previous
From: Hotmail
Date:
Subject: Re: Performance bottleneck. High active sessions but postmaster kernel threads are in a sleep state, low CPU utilization
Next
From: Hotmail
Date:
Subject: Re: Performance bottleneck. High active sessions but postmaster kernel threads are in a sleep state, low CPU utilization