Message-ID: <ea98b11380557874a7bf3a577146786df8ec1da1.camel@j-davis.com>
Subject: Re: Expanding HOT updates for expression and partial indexes
From: Jeff Davis <pgsql@j-davis.com>
To: Greg Burd <greg@burd.me>, "Burd, Greg" <gregburd@amazon.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: Thu, 09 Oct 2025 12:27:15 -0700
In-Reply-To: <CF007F8C-5FCA-4FC5-A7EC-282F8C9D413C@greg.burd.me>
References: <97f0aa72-f172-4673-8b04-533f022c3149@app.fastmail.com>
	 <CF007F8C-5FCA-4FC5-A7EC-282F8C9D413C@greg.burd.me>
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On Tue, 2025-10-07 at 17:36 -0400, Greg Burd wrote:
> After reviewing how updates work in the executor, I discovered that
> during execution the new tuple slot is populated with the information
> from ExecBuildUpdateProjection() and the old tuple, but that most
> importantly for this use case that function created a bitmap of the
> modified columns (the columns specified in the update).=C2=A0 This bitmap
> isn't the same as the one produced by HeapDetermineColumnsInfo() as
> the
> latter excludes attributes that are not changed after testing
> equality
> with the helper function heap_attr_equals() where as the former will
> include attributes that appear in the update but are the same value
> as
> before.=C2=A0 This, happily, is immaterial for the purposes of my functio=
n
> ExecExprIndexesRequireUpdates() which simply needs to check to see if
> index tuples generated are unchanged.=C2=A0 So I had all I needed to run
> the
> checks ahead of acquiring the lock on the buffer.

You're still calling ExecExprIndexesRequireUpdates() from within
heap_update(). Can't you do that inside of ExecUpdatePrologue() or
thereabouts?

Regards,
	Jeff Davis