Re: Increase value of OUTER_VAR

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
Cc: Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Increase value of OUTER_VAR
Date: 2021-03-04 15:16:49
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Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> writes:
> IMO just bumping up the constants from ~65k to 1M is a net loss, for
> most users. We add this to bitmapsets, which means we're using ~8kB with
> the current values, but this jumps to 128kB with this higher value. This
> also means bms_next_member etc. have to walk much more memory, which is
> bound to have some performance impact for everyone.

Hmm, do we really have any places that include OUTER_VAR etc in
bitmapsets? They shouldn't appear in relid sets, for sure.
I agree though that if they did, this would have bad performance

I still think the negative-special-values approach is better.
If there are any places that that would break, we'd find out about
it in short order, rather than having a silent performance lossage.

regards, tom lane

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