Merge pull request #400 from MasahikoSawada/fix_concurrent_vacuums

Fix possible two vacuums concurrently processing the same relfilenode.

bin/pg_repack.c

@@ -189,6 +189,7 @@ typedef struct repack_table
 	Oid				target_tidx;	/* target: toast index OID */
 	Oid				pkid;			/* target: PK OID */
 	Oid				ckid;			/* target: CK OID */
+	Oid				temp_oid;		/* temp: OID */
 	const char	   *create_pktype;	/* CREATE TYPE pk */
 	const char	   *create_log;		/* CREATE TABLE log */
 	const char	   *create_trigger;	/* CREATE TRIGGER repack_trigger */
@@ -910,6 +911,7 @@ repack_one_database(const char *orderby, char *errbuf, size_t errsize)
 		c++; // Skip schemaname
 		table.pkid = getoid(res, i, c++);
 		table.ckid = getoid(res, i, c++);
+		table.temp_oid = InvalidOid; /* filled after creating the temp table */
 
 		if (table.pkid == 0) {
 			ereport(WARNING,
@@ -1537,6 +1539,14 @@ repack_one_table(repack_table *table, const char *orderby)
 	command(sql.data, 0, NULL);
 	command("COMMIT", 0, NULL);
 
+	/* Get OID of the temp table */
+	printfStringInfo(&sql, "SELECT 'repack.table_%u'::regclass::oid",
+					 table->target_oid);
+	res = execute(sql.data, 0, NULL);
+	table->temp_oid = getoid(res, 0, 0);
+	Assert(OidIsValid(table->temp_oid));
+	CLEARPGRES(res);
+
 	/*
 	 * 3. Create indexes on temp table.
 	 */
@@ -1612,6 +1622,20 @@ repack_one_table(repack_table *table, const char *orderby)
 		goto cleanup;
 	}
 
+	/*
+	 * Acquire AccessExclusiveLock on the temp table to prevent concurrent
+	 * operations during swapping relations.
+	 */
+	printfStringInfo(&sql, "LOCK TABLE repack.table_%u IN ACCESS EXCLUSIVE MODE",
+					 table->target_oid);
+	if (!(lock_exclusive(conn2, utoa(table->temp_oid, buffer),
+						 sql.data, false)))
+	{
+		elog(WARNING, "lock_exclusive() failed in conn2 for table_%u",
+			 table->target_oid);
+		goto cleanup;
+	}
+
 	apply_log(conn2, table, 0);
 	params[0] = utoa(table->target_oid, buffer);
 	pgut_command(conn2, "SELECT repack.repack_swap($1)", 1, params);

lib/repack.c

@@ -901,6 +901,24 @@ repack_swap(PG_FUNCTION_ARGS)
 		CommandCounterIncrement();
 	}
 
+	/*
+	 * Sanity check if both relations are locked in access exclusive mode
+	 * before swapping these files.
+	 */
+#if PG_VERSION_NUM >= 120000
+	{
+		LOCKTAG	tag;
+
+		SET_LOCKTAG_RELATION(tag, MyDatabaseId, oid);
+		if (!LockHeldByMe(&tag, AccessExclusiveLock))
+			elog(ERROR, "must hold access exclusive lock on table \"%s\"", relname);
+
+		SET_LOCKTAG_RELATION(tag, MyDatabaseId, oid2);
+		if (!LockHeldByMe(&tag, AccessExclusiveLock))
+			elog(ERROR, "must hold access exclusive lock on table \"table_%u\"", oid);
+	}
+#endif
+
 	/* swap tables. */
 	swap_heap_or_index_files(oid, oid2);
 	CommandCounterIncrement();