public inbox for [email protected]  

help / color / mirror / Atom feed

From: Imseih (AWS), Sami <[email protected]>
To: Bertrand Drouvot <[email protected]>
To: Nathan Bossart <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Track the amount of time waiting due to cost_delay
Date: Mon, 10 Jun 2024 20:12:46 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<ZmcdigI9c8oJ2D4X@nathan>
	<[email protected]>

>> This sounds like useful information to me.

> Thanks for looking at it!

The  VacuumDelay is the only visibility available to
gauge the cost_delay. Having this information
advertised by pg_stat_progress_vacuum as is being proposed
is much better. However, I also think that the
"number of times"  the vacuum went into delay will be needed
as well. Both values will be useful to tune cost_delay and cost_limit. 

It may also make sense to accumulate the total_time in delay
and the number of times delayed in a cumulative statistics [0]
view to allow a user to trend this information overtime.
I don't think this info fits in any of the existing views, i.e.
pg_stat_database, so maybe a new view for cumulative
vacuum stats may be needed. This is likely a separate
discussion, but calling it out here.

>> IIUC you'd need to get information from both pg_stat_progress_vacuum and
>> pg_stat_activity in order to know what percentage of time was being spent
>> in cost delay.  Is that how you'd expect for this to be used in practice?

> Yeah, one could use a query such as:

> select p.*, now() - a.xact_start as duration from pg_stat_progress_vacuum p JOIN pg_stat_activity a using (pid)

Maybe all  progress views should just expose the "beentry->st_activity_start_timestamp " 
to let the user know when the current operation began.


Regards,

Sami Imseih
Amazon Web Services (AWS)


[0] https://www.postgresql.org/docs/current/monitoring-stats.html

view thread (20+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected]
  Subject: Re: Track the amount of time waiting due to cost_delay
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox