Date: Thu, 3 Dec 2020 09:00:51 +0800
From: Julien Rouhaud <rjuju123@gmail.com>
To: Nikolay Samokhvalov <samokhvalov@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: pg_stat_statements oddity with track = all
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On Wed, Dec 02, 2020 at 06:23:54AM -0800, Nikolay Samokhvalov wrote:
> On Tue, Dec 1, 2020 at 10:32 PM Julien Rouhaud <rjuju123@gmail.com> wrote:
> 
> > On Tue, Dec 01, 2020 at 10:08:06PM -0800, Nikolay Samokhvalov wrote:
> > > If all top-level records in pg_stat_statements have "true" in the new
> > > column (is_toplevel), how would this lead to the need to increase
> > > pg_stat_statements.max? The number of records would remain the same, as
> > > before extending pg_stat_statements.
> >
> > If the same query is getting executed both at top level and as a nested
> > statement, two entries will then be created.  That's probably unlikely for
> > things like RI trigger queries, but I don't know what to expect for client
> > application queries.
> >
> 
> Right, but this is how things already work. The extra field you've proposed
> won't increase the number of records so it shouldn't affect how users
> choose pg_stat_statements.max.

The extra field I've proposed would increase the number of records, as it needs
to be a part of the key.  The only alternative would be what Fufi-san
mentioned, i.e. to split plans and calls (for instance plans_toplevel,
plans_nested, calls_toplevel, calls_nested) and let users compute an
approximate value for toplevel counters.