From: Nathan Bossart <nathandbossart@gmail.com>
To: Greg Burd <greg@burd.me>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Expanding HOT updates for expression and partial indexes
Date: Tue, 17 Mar 2026 10:22:02 -0500
Message-ID: <ablxmmcbA_8UFjiN@nathan> (raw)
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<427bfbda-c901-49e4-b725-8ddc41bec23d@app.fastmail.com>
Catching up here. I see that you dropped 0002. Can you explain why that's
no longer needed?
On Mon, Mar 16, 2026 at 04:51:31PM -0400, Greg Burd wrote:
> Refactor executor update logic to determine which indexed columns have
> actually changed during an UPDATE operation rather than leaving this up
> to HeapDetermineColumnsInfo() in heap_update(). Finding this set of
> attributes is not heap-specific, but more general to all table AMs and
> having this information in the executor could inform other decisions
> about when index inserts are required and when they are not regardless
> of the table AM's MVCC implementation strategy.
Nice, this is a crisp motivation statement.
> Development of this feature exposed nondeterministic behavior in three
> existing tests which have been adjusted to avoid inconsistent test
> results due to tuple ordering during heap page scans.
Logistically speaking, these could be nice to get out of the way early as a
prerequisite patch so we can focus on the substance of this patch.
The rest of my comments are from a relatively quick skim. Deeper review to
follow...
> + /*
> + * Reduce the set under review to only the unmodified indexed replica
> + * identity key attributes. idx_attrs is copied (by bms_difference())
> + * not modified here.
> + */
> + attrs = bms_difference(idx_attrs, modified_idx_attrs);
> + attrs = bms_int_members(attrs, rid_attrs);
> +
> + while ((attidx = bms_next_member(attrs, attidx)) >= 0)
Could it be worth moving this loop (and some surrounding code) to a helper
function?
> - * Note: beyond this point, use oldtup not otid to refer to old tuple.
> + * NOTE: beyond this point, use oldtup not otid to refer to old tuple.
nitpick: Please remove unnecessary changes.
> @@ -5269,10 +5269,10 @@ RelationGetIndexPredicate(Relation relation)
> * in expressions (i.e., usable for FKs)
> * INDEX_ATTR_BITMAP_PRIMARY_KEY Columns in the table's primary key
> * (beware: even if PK is deferrable!)
> + * INDEX_ATTR_BITMAP_SUMMARIZED Columns only included in summarizing indexes
> * INDEX_ATTR_BITMAP_IDENTITY_KEY Columns in the table's replica identity
> * index (empty if FULL)
> - * INDEX_ATTR_BITMAP_HOT_BLOCKING Columns that block updates from being HOT
> - * INDEX_ATTR_BITMAP_SUMMARIZED Columns included in summarizing indexes
> + * INDEX_ATTR_BITMAP_INDEXED Columns referenced by indexes
Is the meaning of INDEX_ATTR_BITMAP_SUMMARIZED changing in this patch? I
see you moved it and dropped the "only".
> - Bitmapset *summarizedattrs; /* columns with summarizing indexes */
> + Bitmapset *indexedattrs; /* columns referenced by indexes */
> + Bitmapset *summarizedattrs; /* columns only in summarizing indexes */
But you added an "only" here...
--
nathan
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, greg@burd.me, pgsql@j-davis.com
Subject: Re: Expanding HOT updates for expression and partial indexes
In-Reply-To: <ablxmmcbA_8UFjiN@nathan>
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