Re: pg_stat_statements and "IN" conditions

> On Thu, Feb 13, 2025 at 01:47:01PM GMT, Álvaro Herrera wrote:
> Also, how wed are you to
> "query_id_merge_values" as a name? It's not in any way obvious that
> this is about values in arrays. How about query_id_squash_arrays? Or
> are you thinking in having values in other types of structures squashed
> as well, and that this first patch does it for arrays only but you want
> the GUC to also control some future feature?
>
> (I think I prefer "squash" here as a verb to "merge").

Yeah, when choosing the name I was trying to keep it a bit generic. The
high level goal is to reduce repeated non-essential parts, and arrays of
constants are one clear scenario, but there could be more to it. Having
said that I don't have any particular plans for extending this logic so
far. I've ended up with query_id_squash_values, how does this sound?

> I think calling func_volatile potentially once per array element is not
> good; this might cause dozens/thousands of identical syscache lookups.
> Maybe we can pass an initially NIL list from IsMergeableConstList (as
> List **), which IsMergeableConst fills with OIDs of functions that have
> been checked and found acceptable. Then the second time around we
> search the list first and only do func_volatile() after not finding a
> match.

Good point, added.

> Another thing I didn't quite understand is why you did this rather
> baroque-looking list scan:

I'm pretty sure there was some reason behind it, but when you pointed it
out that reason has promptly vanished in a puff of confusion. Fixed.