Horton

Re: Fix incorrect comments in tuplesort.c

David Rowley <dgrowleyml@gmail.com>

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From: David Rowley <dgrowleyml@gmail.com>
To: cca5507 <cca5507@qq.com>
Cc: "David G. Johnston" <david.g.johnston@gmail.com>, Chao Li <li.evan.chao@gmail.com>, pgsql-hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-12-07T22:09:37Z
Lists: pgsql-hackers 
On Sun, 7 Dec 2025 at 21:34, cca5507 <cca5507@qq.com> wrote:
> I find that the initial size of memtuples array must be more than ALLOCSET_SEPARATE_THRESHOLD
> is not for lower overhead of allocation, but for a bug fixed in 8ea3e7a75c0d22c41c57f59c8b367059b97d0b66.
>
> Attach a new patch.

I find the current comment perfectly understandable and the text
you're proposing to be incorrect. What you might be missing is that
with aset.c, a palloc() request above ALLOCSET_SEPARATE_THRESHOLD is
certain to require a malloc() and a dedicated block. Sizes under that
may be able to use an existing AllocBlock. The comment is effectively
explaining that we don't want to make the array big enough so that a
malloc will always be required. You may need to read
AllocSetContextCreateInternal() around where allocChunkLimit is being
set to understand what this is all about.

David