Re: Add bms_offset_members() function for bitshifting Bitmapsets

From: David Rowley <dgrowleyml(at)gmail(dot)com>
To: Greg Burd <greg(at)burd(dot)me>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Add bms_offset_members() function for bitshifting Bitmapsets
Date: 2026-04-21 01:40:17
Message-ID: CAApHDvqPRUqTVU0=Ewm38UKWOV5Ak1mQXg=+L98Mm9CVpyAmLQ@mail.gmail.com
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On Tue, 21 Apr 2026 at 02:55, Greg Burd <greg(at)burd(dot)me> wrote:
> Were you planning on writing the optimized non-copy version as well? I don't think it is strictly necessary, more a curiosity.
>
> bms_offset_members() -> new bms, might repalloc() replaces existing loops you've found
> bms_shift_members() -> bms is modified in place and fits your new use case a bit better

Not at this stage. The v1 patch did modify the set in-place, so the
code is there if we ever need it. I didn't find any need for it in our
current code. The selective tuple deforming patch I'm working on could
use it, but I doubt it's worth the trouble for 1 caller. It's just for
something that happens during create_plan(), so 1 more allocation in
that code likely isn't going to be noticed.

David

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