Date: Fri, 28 Aug 2026 10:02:42 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: pg_stat_get_autovacuum_scores ignores the main table's
 reloptions for TOAST tables
Message-ID: <apGjEvo15Z5oKHEM@nathan>
References: 
 <CAD21AoB1CJRVfCDh8qYuD3eueiygXxk7F3nybgjN0RZXSD-QUw@mail.gmail.com>
 <apGJqfd2xyAcUGKZ@nathan>
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="S+XuMUjMztxz0jco"
Content-Disposition: inline
In-Reply-To: <apGJqfd2xyAcUGKZ@nathan>
Archived-At: <https://www.postgresql.org/message-id/apGjEvo15Z5oKHEM%40nathan>
Precedence: bulk

--S+XuMUjMztxz0jco
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

Here is a patch.

-- 
nathan

--S+XuMUjMztxz0jco
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename=v1-0001-Fix-pg_stat_autovacuum_scores-for-TOAST-tables.patch

From cd6e33acf8086d0c1b5b2d3fb0d177ea5c77cb8f Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Fri, 28 Aug 2026 09:54:06 -0500
Subject: [PATCH v1 1/1] Fix pg_stat_autovacuum_scores for TOAST tables.

In v19, pg_stat_autovacuum_scores computes a TOAST table's scores
from its own storage parameters alone.  Autovacuum instead falls
back to the main table's parameters when the TOAST table has none
of its own, so the view may report scores that don't match what
autovacuum would calculate.  This contradicts the documented
promise that the view generates its results the same way autovacuum
workers do.  To fix, teach the view to do the same fallback.  As in
do_autovacuum(), we cannot know a TOAST table's parameters until we
have seen its main relation, so the view now makes a preliminary
pass over pg_class to collect the main relations' parameters.

Commit fad70a09ff for v20 improved autovacuum's handling of TOAST
storage parameters and adjusted the view to match, but it was
deemed too intrusive to back-patch.  This fix is for v19 only.

Oversight in commit 87f61f0c82.

Reported-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/CAD21AoB1CJRVfCDh8qYuD3eueiygXxk7F3nybgjN0RZXSD-QUw%40mail.gmail.com
Backpatch-through: 19 only
---
 src/backend/postmaster/autovacuum.c | 75 ++++++++++++++++++++++++++++-
 1 file changed, 73 insertions(+), 2 deletions(-)

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 0c975d0eda6..089b9c468a5 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -3652,6 +3652,8 @@ pg_stat_get_autovacuum_scores(PG_FUNCTION_ARGS)
 	TableScanDesc scan;
 	HeapTuple	tup;
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	HTAB	   *table_toast_map;
+	HASHCTL		ctl;
 
 	InitMaterializedSRF(fcinfo, 0);
 
@@ -3660,13 +3662,64 @@ pg_stat_get_autovacuum_scores(PG_FUNCTION_ARGS)
 	recentXid = ReadNextTransactionId();
 	recentMulti = ReadNextMultiXactId();
 
-	/* scan pg_class */
+	/* create hash table for toast <-> main relid mapping */
+	ctl.keysize = sizeof(Oid);
+	ctl.entrysize = sizeof(av_relation);
+	ctl.hcxt = CurrentMemoryContext;
+	table_toast_map = hash_create("TOAST to main relid map",
+								  100,
+								  &ctl,
+								  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
 	rel = table_open(RelationRelationId, AccessShareLock);
+
+	/*
+	 * Do an initial pass over pg_class to collect the main relations'
+	 * autovacuum paramters, which a TOAST table with none of its own
+	 * inherits.  We cannot gather these as we go, since a TOAST table may
+	 * precede its main relation in the scan.
+	 */
 	scan = table_beginscan_catalog(rel, 0, NULL);
 	while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
 	{
 		Form_pg_class form = (Form_pg_class) GETSTRUCT(tup);
 		AutoVacOpts *avopts;
+		av_relation *hentry;
+		bool		found;
+
+		/* skip ineligible entries */
+		if (form->relkind != RELKIND_RELATION &&
+			form->relkind != RELKIND_MATVIEW)
+			continue;
+		if (form->relpersistence == RELPERSISTENCE_TEMP)
+			continue;
+		if (!OidIsValid(form->reltoastrelid))
+			continue;
+
+		avopts = extract_autovac_opts(tup, RelationGetDescr(rel));
+		if (avopts == NULL)
+			continue;
+
+		hentry = hash_search(table_toast_map, &form->reltoastrelid,
+							 HASH_ENTER, &found);
+		Assert(!found);			/* rels cannot share a TOAST table */
+
+		/* hash_search already filled in the key */
+		hentry->ar_relid = form->oid;
+		hentry->ar_hasrelopts = true;
+		memcpy(&hentry->ar_reloptions, avopts, sizeof(AutoVacOpts));
+
+		pfree(avopts);
+	}
+	table_endscan(scan);
+
+	/* now scan pg_class again to compute the scores */
+	scan = table_beginscan_catalog(rel, 0, NULL);
+	while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
+	{
+		Form_pg_class form = (Form_pg_class) GETSTRUCT(tup);
+		AutoVacOpts *avopts;
+		bool		free_avopts = false;
 		bool		dovacuum;
 		bool		doanalyze;
 		bool		wraparound;
@@ -3682,13 +3735,30 @@ pg_stat_get_autovacuum_scores(PG_FUNCTION_ARGS)
 		if (form->relpersistence == RELPERSISTENCE_TEMP)
 			continue;
 
+		/*
+		 * fetch reloptions -- if this toast table does not have them, try the
+		 * main rel
+		 */
+		avopts = extract_autovac_opts(tup, RelationGetDescr(rel));
+		if (avopts)
+			free_avopts = true;
+		else if (form->relkind == RELKIND_TOASTVALUE)
+		{
+			av_relation *hentry;
+			bool		found;
+
+			hentry = hash_search(table_toast_map, &form->oid, HASH_FIND, &found);
+			if (found && hentry->ar_hasrelopts)
+				avopts = &hentry->ar_reloptions;
+		}
+
 		avopts = extract_autovac_opts(tup, RelationGetDescr(rel));
 		relation_needs_vacanalyze(form->oid, avopts, form,
 								  effective_multixact_freeze_max_age,
 								  LOG_NEVER,
 								  &dovacuum, &doanalyze, &wraparound,
 								  &scores);
-		if (avopts)
+		if (free_avopts)
 			pfree(avopts);
 
 		vals[0] = ObjectIdGetDatum(form->oid);
@@ -3706,6 +3776,7 @@ pg_stat_get_autovacuum_scores(PG_FUNCTION_ARGS)
 	}
 	table_endscan(scan);
 	table_close(rel, AccessShareLock);
+	hash_destroy(table_toast_map);
 
 	return (Datum) 0;
 }
-- 
2.55.0


--S+XuMUjMztxz0jco--