Date: Tue, 10 Jul 2018 13:38:28 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Patrick Hemmer <postgresql@stormcloud9.net>
Cc: pgsql-performance@lists.postgresql.org,
	Adrien Nayrat <adrien.nayrat@anayrat.info>
Subject: Re: performance statistics monitoring without spamming logs
Message-ID: <20180710183828.GB3890@telsasoft.com>
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On Tue, Jul 10, 2018 at 01:54:12PM -0400, Patrick Hemmer wrote:
> I'm looking for a way of gathering performance stats in a more usable
> way than turning on `log_statement_stats` (or other related modules).
> The problem I have with the log_*_stats family of modules is that they
> log every single query, which makes them unusable in production. Aside
> from consuming space, there's also the problem that the log system
> wouldn't be able to keep up with the rate.
> 
> There are a couple ideas that pop into mind that would make these stats
> more usable:
> 1. Only log when the statement would otherwise already be logged. Such
> as due to the `log_statement` or `log_min_duration_statement` settings.

Did you see: (Added Adrien to Cc);
https://commitfest.postgresql.org/18/1691/

I don't think the existing patch does what you want, but perhaps all that's
needed is this:

        if (save_log_statement_stats)
+               if (log_sample_rate==1 || was_logged)
                ShowUsage("EXECUTE MESSAGE STATISTICS");

In any case, I'm thinking that your request could/should be considered by
whatever future patch implements sampling (if not implemented/included in the
patch itself).

If that doesn't do what's needed, that patch might still be a good crash course
in how to start implementing what you need (perhaps on top of that patch).

> 2. Make stats available in `pg_stat_statements` (or alternate view that
> could be joined on). The block stats are already available here, but
> others like CPU usage, page faults, and context switches are not.

pg_stat_statements is ./contrib/pg_stat_statements/pg_stat_statements.c which is 3k LOC.

getrusage stuff and log_*_stat stuff is in src/backend/tcop/postgres.c

Justin