| 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 |
| Message-ID: | 1359871.1614871009@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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
consequences.
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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