Re: compute_query_id and pg_stat_statements

Hi,

On 2021-04-26 13:43:31 -0400, Alvaro Herrera wrote:
> I think it's straightforward, if we decouple the tri-valued enum used
> for guc.c purposes from a separate boolean that actually enables the
> feature.  GUC sets the boolean to "off" initially when it sees the enum
> as "auto", and then pg_stat_statement's _PG_init modifies it during its
> own startup as needed.

> So the user can turn the GUC off, and then pg_stat_statement does
> nothing and there is no performance drawback; or leave it "auto" and
> it'll only compute query_id if pg_stat_statement is loaded; or leave it
> on if they want the query_id for other purposes.

I think that's the right direction. I wonder though if we shouldn't go a
bit further. Have one guc that determines the "query id provider" (NULL
or a shared library), and one GUC that configures whether query-id is
computed (never, on-demand/auto, always). For the provider GUC load the
.so and look up a function with some well known name.

Greetings,

Andres Freund