|From:||Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>|
|To:||Julien Rouhaud <rjuju123(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|Subject:||Re: Make EXPLAIN generate a generic plan for a parameterized query|
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On Wed, 2022-10-12 at 00:03 +0800, Julien Rouhaud wrote:
> On Tue, Oct 11, 2022 at 09:49:14AM -0400, Tom Lane wrote:
> > I think it might be better to drive it off an explicit EXPLAIN option,
> > perhaps
> > EXPLAIN (GENERIC_PLAN) SELECT * FROM tab WHERE col = $1;
> > If you're trying to investigate custom-plan behavior, then you
> > need to supply concrete parameter values somewhere, so I think
> > this approach is fine for that case. (Shoehorning parameter
> > values into EXPLAIN options seems like it'd be a bit much.)
> > However, investigating generic-plan behavior this way is tedious,
> > since you have to invent irrelevant parameter values, plus mess
> > with plan_cache_mode or else run the explain half a dozen times.
> > So I can get behind having a more convenient way for that.
> One common use case is tools identifying a slow query using pg_stat_statements,
> identifying some missing indexes and then wanting to check whether the index
> should be useful using some hypothetical index.
> FTR I'm working on such a project and for now we have to go to great lengths
> trying to "unjumble" such queries, so having a way to easily get the answer for
> a generic plan would be great.
Thanks for the suggestions and the encouragement. Here is a patch that
implements it with an EXPLAIN option named GENERIC_PLAN.
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