Re: compute_query_id and pg_stat_statements

On Thu, May 13, 2021 at 11:30:56AM +0900, Kyotaro Horiguchi wrote:
> At Thu, 13 May 2021 11:26:29 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> > At Thu, 13 May 2021 10:02:45 +0800, Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote in
> > > On Thu, May 13, 2021 at 10:51:52AM +0900, Kyotaro Horiguchi wrote:
> > > > At Thu, 13 May 2021 09:59:43 +0900 (JST), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in
> > > > > How about adding a GUC_INTERNAL "current_query_provider" or such?
> > > >
> > > > On the second thought, I wonder why we don't just call JumbleQuery in
> > > > pgss_post_parse_analyze when compute_query_id is "off".
> > >
> > > Because not generating a query_id for a custom query_id implementation is a
> > > valid use case for queries that are known to lead to huge pg_stat_statements
> > > overhead, as I mentioned in [1]. For the record I implemented that in
> > > pg_queryid (optionally don't generate query_id for queries referencing a temp
> > > relation) yesterday evening as a POC for that approach.
> >
> > Yes, I know. So I said that "if not yet called". I believe any "real"
> > alternative query-id provider is supposed to be hooked "before"
> > pg_stat_statements. (It is a kind of magic to control the order of
> > plugins, though..) When the alternative provider generated a query_id
> > (that is, it has set jstate), pg_stat_statment doesn't call the
> > in-core JumbleQuery and uses the givin query_id.
>
> Forgot to mention, I think that the state "query_id provider is active
> but it has not assigned one to this query" can be signaled by
> jstate=<non-null> and query_id = 0.

I assume that you mean "third-party query_id provider" here, as the core one
will always return a non-zero query_id?

I guess it could work, but a lot of people are complaining that having
compute_query_id = [ off | on | auto ] is too confusing, so I don't see how
having "off" means "sometimes off, sometimes on" is going to be any clearer for
users.