Fix concurrent indexing operations with temporary tables

Attempting to use CREATE INDEX, DROP INDEX or REINDEX with CONCURRENTLY
on a temporary relation with ON COMMIT actions triggered unexpected
errors because those operations use multiple transactions internally to
complete their work.  Here is for example one confusing error when using
ON COMMIT DELETE ROWS:
ERROR:  index "foo" already contains data

Issues related to temporary relations and concurrent indexing are fixed
in this commit by enforcing the non-concurrent path to be taken for
temporary relations even if using CONCURRENTLY, transparently to the
user.  Using a non-concurrent path does not matter in practice as locks
cannot be taken on a temporary relation by a session different than the
one owning the relation, and the non-concurrent operation is more
effective.

The problem exists with REINDEX since v12 with the introduction of
CONCURRENTLY, and with CREATE/DROP INDEX since CONCURRENTLY exists for
those commands.  In all supported versions, this caused only confusing
error messages to be generated.  Note that with REINDEX, it was also
possible to issue a REINDEX CONCURRENTLY for a temporary relation owned
by a different session, leading to a server crash.

The idea to enforce transparently the non-concurrent code path for
temporary relations comes originally from Andres Freund.

Reported-by: Manuel Rigger
Author: Michael Paquier, Heikki Linnakangas
Reviewed-by: Andres Freund, Álvaro Herrera, Heikki Linnakangas
Discussion: https://postgr.es/m/CA+u7OA6gP7YAeCguyseusYcc=uR8+ypjCcgDDCTzjQ+k6S9ksQ@mail.gmail.com
Backpatch-through: 9.4

5 files changed, 102 insertions, 8 deletions

diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index bc20d7c750b..bb7d9813273 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1494,6 +1494,15 @@ index_drop(Oid indexId, bool concurrent)
 	LOCKMODE	lockmode;
 
 	/*
+	 * A temporary relation uses a non-concurrent DROP.  Other backends can't
+	 * access a temporary relation, so there's no harm in grabbing a stronger
+	 * lock (see comments in RemoveRelations), and a non-concurrent DROP is
+	 * more efficient.
+	 */
+	Assert(get_rel_persistence(indexId) != RELPERSISTENCE_TEMP ||
+		   !concurrent);
+
+	/*
 	 * To drop an index safely, we must grab exclusive lock on its parent
 	 * table.  Exclusive lock on the index alone is insufficient because
 	 * another backend might be about to execute a query on the parent table.
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 1faaaf625d9..568a32bb4ec 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -335,6 +335,7 @@ DefineIndex(Oid relationId,
 			bool skip_build,
 			bool quiet)
 {
+	bool		concurrent;
 	char	   *indexRelationName;
 	char	   *accessMethodName;
 	Oid		   *typeObjectId;
@@ -372,6 +373,18 @@ DefineIndex(Oid relationId,
 	int			i;
 
 	/*
+	 * Force non-concurrent build on temporary relations, even if CONCURRENTLY
+	 * was requested.  Other backends can't access a temporary relation, so
+	 * there's no harm in grabbing a stronger lock, and a non-concurrent DROP
+	 * is more efficient.  Do this before any use of the concurrent option is
+	 * done.
+	 */
+	if (stmt->concurrent && get_rel_persistence(relationId) != RELPERSISTENCE_TEMP)
+		concurrent = true;
+	else
+		concurrent = false;
+
+	/*
 	 * count key attributes in index
 	 */
 	numberOfKeyAttributes = list_length(stmt->indexParams);
@@ -413,7 +426,7 @@ DefineIndex(Oid relationId,
 	 * parallel workers under the control of certain particular ambuild
 	 * functions will need to be updated, too.
 	 */
-	lockmode = stmt->concurrent ? ShareUpdateExclusiveLock : ShareLock;
+	lockmode = concurrent ? ShareUpdateExclusiveLock : ShareLock;
 	rel = heap_open(relationId, lockmode);
 
 	relationId = RelationGetRelid(rel);
@@ -457,6 +470,12 @@ DefineIndex(Oid relationId,
 	partitioned = rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE;
 	if (partitioned)
 	{
+		/*
+		 * Note: we check 'stmt->concurrent' rather than 'concurrent', so that
+		 * the error is thrown also for temporary tables.  Seems better to be
+		 * consistent, even though we could do it on temporary table because
+		 * we're not actually doing it concurrently.
+		 */
 		if (stmt->concurrent)
 			ereport(ERROR,
 					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
@@ -645,8 +664,8 @@ DefineIndex(Oid relationId,
 	indexInfo->ii_ExclusionStrats = NULL;
 	indexInfo->ii_Unique = stmt->unique;
 	/* In a concurrent build, mark it not-ready-for-inserts */
-	indexInfo->ii_ReadyForInserts = !stmt->concurrent;
-	indexInfo->ii_Concurrent = stmt->concurrent;
+	indexInfo->ii_ReadyForInserts = !concurrent;
+	indexInfo->ii_Concurrent = concurrent;
 	indexInfo->ii_BrokenHotChain = false;
 	indexInfo->ii_ParallelWorkers = 0;
 	indexInfo->ii_Am = accessMethodId;
@@ -814,7 +833,7 @@ DefineIndex(Oid relationId,
 	 * A valid stmt->oldNode implies that we already have a built form of the
 	 * index.  The caller should also decline any index build.
 	 */
-	Assert(!OidIsValid(stmt->oldNode) || (skip_build && !stmt->concurrent));
+	Assert(!OidIsValid(stmt->oldNode) || (skip_build && !concurrent));
 
 	/*
 	 * Make the catalog entries for the index, including constraints. This
@@ -825,11 +844,11 @@ DefineIndex(Oid relationId,
 	flags = constr_flags = 0;
 	if (stmt->isconstraint)
 		flags |= INDEX_CREATE_ADD_CONSTRAINT;
-	if (skip_build || stmt->concurrent || partitioned)
+	if (skip_build || concurrent || partitioned)
 		flags |= INDEX_CREATE_SKIP_BUILD;
 	if (stmt->if_not_exists)
 		flags |= INDEX_CREATE_IF_NOT_EXISTS;
-	if (stmt->concurrent)
+	if (concurrent)
 		flags |= INDEX_CREATE_CONCURRENT;
 	if (partitioned)
 		flags |= INDEX_CREATE_PARTITIONED;
@@ -1107,7 +1126,7 @@ DefineIndex(Oid relationId,
 		return address;
 	}
 
-	if (!stmt->concurrent)
+	if (!concurrent)
 	{
 		/* Close the heap and we're done, in the non-concurrent case */
 		heap_close(rel, NoLock);
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index a120a18f029..38386fb9cf9 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1106,7 +1106,11 @@ RemoveRelations(DropStmt *drop)
 	/* DROP CONCURRENTLY uses a weaker lock, and has some restrictions */
 	if (drop->concurrent)
 	{
-		flags |= PERFORM_DELETION_CONCURRENTLY;
+		/*
+		 * Note that for temporary relations this lock may get upgraded
+		 * later on, but as no other session can access a temporary
+		 * relation, this is actually fine.
+		 */
 		lockmode = ShareUpdateExclusiveLock;
 		Assert(drop->removeType == OBJECT_INDEX);
 		if (list_length(drop->objects) != 1)
@@ -1197,6 +1201,18 @@ RemoveRelations(DropStmt *drop)
 			continue;
 		}
 
+		/*
+		 * Decide if concurrent mode needs to be used here or not.  The
+		 * relation persistence cannot be known without its OID.
+		 */
+		if (drop->concurrent &&
+			get_rel_persistence(relOid) != RELPERSISTENCE_TEMP)
+		{
+			Assert(list_length(drop->objects) == 1 &&
+				   drop->removeType == OBJECT_INDEX);
+			flags |= PERFORM_DELETION_CONCURRENTLY;
+		}
+
 		/* OK, we're ready to delete this one */
 		obj.classId = RelationRelationId;
 		obj.objectId = relOid;
diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index e7d7c7aee6d..c3deccca570 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -2571,6 +2571,31 @@ Indexes:
     "concur_index5" btree (f2) WHERE f1 = 'x'::text
     "std_index" btree (f2)
 
+-- Temporary tables with concurrent builds and on-commit actions
+-- CONCURRENTLY used with CREATE INDEX and DROP INDEX is ignored.
+-- PRESERVE ROWS, the default.
+CREATE TEMP TABLE concur_temp (f1 int, f2 text)
+  ON COMMIT PRESERVE ROWS;
+INSERT INTO concur_temp VALUES (1, 'foo'), (2, 'bar');
+CREATE INDEX CONCURRENTLY concur_temp_ind ON concur_temp(f1);
+DROP INDEX CONCURRENTLY concur_temp_ind;
+DROP TABLE concur_temp;
+-- ON COMMIT DROP
+BEGIN;
+CREATE TEMP TABLE concur_temp (f1 int, f2 text)
+  ON COMMIT DROP;
+INSERT INTO concur_temp VALUES (1, 'foo'), (2, 'bar');
+-- Fails when running in a transaction.
+CREATE INDEX CONCURRENTLY concur_temp_ind ON concur_temp(f1);
+ERROR:  CREATE INDEX CONCURRENTLY cannot run inside a transaction block
+COMMIT;
+-- ON COMMIT DELETE ROWS
+CREATE TEMP TABLE concur_temp (f1 int, f2 text)
+  ON COMMIT DELETE ROWS;
+INSERT INTO concur_temp VALUES (1, 'foo'), (2, 'bar');
+CREATE INDEX CONCURRENTLY concur_temp_ind ON concur_temp(f1);
+DROP INDEX CONCURRENTLY concur_temp_ind;
+DROP TABLE concur_temp;
 --
 -- Try some concurrent index drops
 --
diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql
index 283c4e6c18e..668076e2159 100644
--- a/src/test/regress/sql/create_index.sql
+++ b/src/test/regress/sql/create_index.sql
@@ -825,6 +825,31 @@ VACUUM FULL concur_heap;
 REINDEX TABLE concur_heap;
 \d concur_heap
 
+-- Temporary tables with concurrent builds and on-commit actions
+-- CONCURRENTLY used with CREATE INDEX and DROP INDEX is ignored.
+-- PRESERVE ROWS, the default.
+CREATE TEMP TABLE concur_temp (f1 int, f2 text)
+  ON COMMIT PRESERVE ROWS;
+INSERT INTO concur_temp VALUES (1, 'foo'), (2, 'bar');
+CREATE INDEX CONCURRENTLY concur_temp_ind ON concur_temp(f1);
+DROP INDEX CONCURRENTLY concur_temp_ind;
+DROP TABLE concur_temp;
+-- ON COMMIT DROP
+BEGIN;
+CREATE TEMP TABLE concur_temp (f1 int, f2 text)
+  ON COMMIT DROP;
+INSERT INTO concur_temp VALUES (1, 'foo'), (2, 'bar');
+-- Fails when running in a transaction.
+CREATE INDEX CONCURRENTLY concur_temp_ind ON concur_temp(f1);
+COMMIT;
+-- ON COMMIT DELETE ROWS
+CREATE TEMP TABLE concur_temp (f1 int, f2 text)
+  ON COMMIT DELETE ROWS;
+INSERT INTO concur_temp VALUES (1, 'foo'), (2, 'bar');
+CREATE INDEX CONCURRENTLY concur_temp_ind ON concur_temp(f1);
+DROP INDEX CONCURRENTLY concur_temp_ind;
+DROP TABLE concur_temp;
+
 --
 -- Try some concurrent index drops
 --