Re: pg_stat_statements oddity with track = all

On Tue, Dec 1, 2020 at 8:05 PM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:

> Hi,
>
> Someone raised an interested point recently on pg_stat_kcache extension for
> handling nested statements, which also applies to pg_stat_statements.
>
...

> The only idea I have for that is to add a new field to entry key, for
> instance
> is_toplevel.

This particular problem often bothered me when dealing with
pg_stat_statements contents operating under "track = all" (especially when
performing the aggregated analysis, like you showed).

I think the idea of having a flag to distinguish the top-level entries is
great.

> The immediate cons is obviously that it could amplify quite a lot
> the number of entries tracked, so people may need to increase
> pg_stat_statements.max to avoid slowdown if that makes them reach frequent
> entry eviction.
>

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.