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Date: Fri, 10 Jul 2026 16:22:04 +0200
From: =?utf-8?Q?=C3=81lvaro?= Herrera <alvherre@kurilemu.de>
To: cca5507 <cca5507@qq.com>
Cc: pgsql-hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Do not lock tables in get_tables_to_repack
Message-ID: <alD9l-XlCuu3eUEe@alvherre.pgsql>
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On 2026-Jul-08, cca5507 wrote:

> -                       classtup = SearchSysCache1(RELOID, ObjectIdGetDatum(index->indrelid));
> +                       classtup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(index->indrelid));
> 
> Do we really need to copy it? We hold a refcount on it so it won't be freed
> until we release it. Otherwise LGTM.

Yeah, I guess it doesn't matter.  I have removed the copy and updated
some comments.  I also realized that there are some places where we
weren't dealing correctly with the possibility that the relation goes
away, or is replaced with something different, so I added that too.

While looking at it I also realized that get_tables_to_repack_partitioned
is likewise not careful enough about it: we do IndexGetRelation(, false)
which fails hard if the pg_index tuple cannot be found, which is the
wrong thing to do.

At the same time, it's annoying that half of the code that clearly
belongs in that routine is actually in ExecRepack().  I moved that to
where it rightfully belongs.  (The only somewhat annoying thing is that
we have to NULL-out the Relation pointer after returning; but that's not
*too* bad IMO.)

Any opinions on this?

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"No me acuerdo, pero no es cierto.  No es cierto, y si fuera cierto,
 no me acuerdo."                 (Augusto Pinochet a una corte de justicia)

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From e192b820d83c6c8a99e901178ec891a4db59da07 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=81lvaro=20Herrera?= <alvherre@kurilemu.de>
Date: Thu, 9 Jul 2026 16:55:12 +0200
Subject: [PATCH] change get_tables_to_repack_partitioned

---
 src/backend/commands/repack.c | 127 +++++++++++++++++-----------------
 1 file changed, 65 insertions(+), 62 deletions(-)

diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 02883fe34a4..b3589ceff51 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -169,8 +169,8 @@ static void copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldInde
 							MultiXactId *pCutoffMulti);
 static List *get_tables_to_repack(RepackCommand cmd, bool usingindex,
 								  MemoryContext permcxt);
-static List *get_tables_to_repack_partitioned(RepackCommand cmd,
-											  Oid relid, bool rel_is_index,
+static List *get_tables_to_repack_partitioned(RepackStmt *stmt,
+											  Relation rel,
 											  MemoryContext permcxt);
 static bool repack_is_permitted_for_relation(RepackCommand cmd,
 											 Oid relid, Oid userid);
@@ -387,58 +387,8 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel)
 	}
 	else
 	{
-		Oid			relid;
-		bool		rel_is_index;
-
-		Assert(rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
-
-		/*
-		 * If USING INDEX was specified, resolve the index name now and pass
-		 * it down.
-		 */
-		if (stmt->usingindex)
-		{
-			/*
-			 * If no index name was specified when repacking a partitioned
-			 * table, punt for now.  Maybe we can improve this later.
-			 */
-			if (!stmt->indexname)
-			{
-				if (stmt->command == REPACK_COMMAND_CLUSTER)
-					ereport(ERROR,
-							errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-							errmsg("there is no previously clustered index for table \"%s\"",
-								   RelationGetRelationName(rel)));
-				else
-					ereport(ERROR,
-							errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-					/*- translator: first %s is name of a SQL command, eg. REPACK */
-							errmsg("cannot execute %s on partitioned table \"%s\" USING INDEX with no index name",
-								   RepackCommandAsString(stmt->command),
-								   RelationGetRelationName(rel)));
-			}
-
-			relid = determine_clustered_index(rel, stmt->usingindex,
-											  stmt->indexname);
-			if (!OidIsValid(relid))
-				elog(ERROR, "unable to determine index to cluster on");
-			check_index_is_clusterable(rel, relid, AccessExclusiveLock);
-
-			rel_is_index = true;
-		}
-		else
-		{
-			relid = RelationGetRelid(rel);
-			rel_is_index = false;
-		}
-
-		rtcs = get_tables_to_repack_partitioned(stmt->command,
-												relid, rel_is_index,
-												repack_context);
-
-		/* close parent relation, releasing lock on it */
-		table_close(rel, AccessExclusiveLock);
-		rel = NULL;
+		rtcs = get_tables_to_repack_partitioned(stmt, rel, repack_context);
+		rel = NULL;			/* clobber no longer valid pointer */
 	}
 
 	/* Commit to get out of starting transaction */
@@ -2255,19 +2205,66 @@ get_tables_to_repack(RepackCommand cmd, bool usingindex, MemoryContext permcxt)
 }
 
 /*
- * Given a partitioned table or its index, return a list of RelToCluster for
- * all the leaf child tables/indexes.
+ * Resolve a partitioned table named as target of REPACK to the list of
+ * its partitions, and return it as a list of RelToCluster.
  *
- * 'rel_is_index' tells whether 'relid' is that of an index (true) or of the
- * owning relation.
+ * The partitioned table in question was already opened and locked by caller
+ * and is given as argument; it is closed and unlocked here before return.
  */
 static List *
-get_tables_to_repack_partitioned(RepackCommand cmd, Oid relid,
-								 bool rel_is_index, MemoryContext permcxt)
+get_tables_to_repack_partitioned(RepackStmt *stmt, Relation rel,
+								 MemoryContext permcxt)
 {
+	Oid			relid;
+	bool		rel_is_index;
 	List	   *inhoids;
 	List	   *rtcs = NIL;
 
+	Assert(rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
+	Assert(CheckRelationLockedByMe(rel, AccessExclusiveLock, false));
+
+	/*
+	 * We find the list of tables by looking for inheritors.  If USING INDEX
+	 * was given, look for inheritors of that index, whose name we resolve now.
+	 *
+	 * Otherwise we look for inheritors of the table itself.
+	 */
+	if (stmt->usingindex)
+	{
+		/*
+		 * If no index name was specified when repacking a partitioned
+		 * table, punt for now.  Maybe we can improve this later.
+		 */
+		if (!stmt->indexname)
+		{
+			if (stmt->command == REPACK_COMMAND_CLUSTER)
+				ereport(ERROR,
+						errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						errmsg("there is no previously clustered index for table \"%s\"",
+							   RelationGetRelationName(rel)));
+			else
+				ereport(ERROR,
+						errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						/*- translator: first %s is name of a SQL command, eg. REPACK */
+						errmsg("cannot execute %s on partitioned table \"%s\" USING INDEX with no index name",
+							   RepackCommandAsString(stmt->command),
+							   RelationGetRelationName(rel)));
+		}
+
+		relid = determine_clustered_index(rel, stmt->usingindex,
+										  stmt->indexname);
+		if (!OidIsValid(relid))
+			elog(ERROR, "unable to determine index to cluster on");
+		check_index_is_clusterable(rel, relid, AccessExclusiveLock);
+
+		rel_is_index = true;
+	}
+	else
+	{
+		relid = RelationGetRelid(rel);
+		rel_is_index = false;
+	}
+
 	/*
 	 * Do not lock the children until they're processed.  Note that we do hold
 	 * a lock on the parent partitioned table.
@@ -2286,7 +2283,9 @@ get_tables_to_repack_partitioned(RepackCommand cmd, Oid relid,
 			if (get_rel_relkind(child_oid) != RELKIND_INDEX)
 				continue;
 
-			table_oid = IndexGetRelation(child_oid, false);
+			table_oid = IndexGetRelation(child_oid, true);
+			if (!OidIsValid(table_oid))
+				continue;
 			index_oid = child_oid;
 		}
 		else
@@ -2304,7 +2303,8 @@ get_tables_to_repack_partitioned(RepackCommand cmd, Oid relid,
 		 * leaf partition despite having them on the partitioned table.  Skip
 		 * if so.
 		 */
-		if (!repack_is_permitted_for_relation(cmd, table_oid, GetUserId()))
+		if (!repack_is_permitted_for_relation(stmt->command, table_oid,
+											  GetUserId()))
 			continue;
 
 		/* Use a permanent memory context for the result list */
@@ -2316,6 +2316,9 @@ get_tables_to_repack_partitioned(RepackCommand cmd, Oid relid,
 		MemoryContextSwitchTo(oldcxt);
 	}
 
+	/* close parent relation, releasing lock on it */
+	table_close(rel, AccessExclusiveLock);
+
 	return rtcs;
 }
 
-- 
2.47.3


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