Hello,
As we are currently experiencing a FSM corruption issue [1], we need to
rebuild FSM when we detect it.
I noticed we have something to truncate a visibility map, but nothing for the
freespace map, so I propose the attached (liberally copied from the VM
counterpart) to allow to truncate a FSM without incurring downtime, as
currently our only options are to either VACUUM FULL the table or stop the
cluster and remove the FSM manually.
Does that seem correct ?
[1] https://www.postgresql.org/message-id/flat/
1925490.taCxCBeP46%40aivenlaptop#7ace95c95cab17b6d92607e5362984ac
--
Ronan Dunklau
>From b3e28e4542311094ee7177b39cc9cdf3672d1b55 Mon Sep 17 00:00:00 2001
From: Ronan Dunklau <ronan.dunk...@aiven.io>
Date: Fri, 1 Mar 2024 08:57:49 +0100
Subject: [PATCH] Provide a pg_truncate_freespacemap function.
Similar to the pg_truncate_visibilitymap function, this one allows to
avoid downtime to fix an FSM in the case a corruption event happens
---
contrib/pg_freespacemap/Makefile | 5 +-
.../pg_freespacemap--1.2--1.3.sql | 13 +++++
contrib/pg_freespacemap/pg_freespacemap.c | 58 +++++++++++++++++++
.../pg_freespacemap/pg_freespacemap.control | 2 +-
4 files changed, 75 insertions(+), 3 deletions(-)
create mode 100644 contrib/pg_freespacemap/pg_freespacemap--1.2--1.3.sql
diff --git a/contrib/pg_freespacemap/Makefile b/contrib/pg_freespacemap/Makefile
index b48e4b255bc..0f4b52f5812 100644
--- a/contrib/pg_freespacemap/Makefile
+++ b/contrib/pg_freespacemap/Makefile
@@ -6,8 +6,9 @@ OBJS = \
pg_freespacemap.o
EXTENSION = pg_freespacemap
-DATA = pg_freespacemap--1.1.sql pg_freespacemap--1.1--1.2.sql \
- pg_freespacemap--1.0--1.1.sql
+DATA = pg_freespacemap--1.1.sql pg_freespacemap--1.2--1.3.sql \
+ pg_freespacemap--1.1--1.2.sql \
+ pg_freespacemap--1.0--1.1.sql
PGFILEDESC = "pg_freespacemap - monitoring of free space map"
REGRESS_OPTS = --temp-config $(top_srcdir)/contrib/pg_freespacemap/pg_freespacemap.conf
diff --git a/contrib/pg_freespacemap/pg_freespacemap--1.2--1.3.sql b/contrib/pg_freespacemap/pg_freespacemap--1.2--1.3.sql
new file mode 100644
index 00000000000..1f25877a175
--- /dev/null
+++ b/contrib/pg_freespacemap/pg_freespacemap--1.2--1.3.sql
@@ -0,0 +1,13 @@
+/* contrib/pg_freespacemap/pg_freespacemap--1.2--1.3.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION pg_freespacemap UPDATE TO '1.3'" to load this file. \quit
+
+CREATE FUNCTION pg_truncate_freespace_map(regclass)
+RETURNS void
+AS 'MODULE_PATHNAME', 'pg_truncate_freespace_map'
+LANGUAGE C STRICT
+PARALLEL UNSAFE;
+
+
+
diff --git a/contrib/pg_freespacemap/pg_freespacemap.c b/contrib/pg_freespacemap/pg_freespacemap.c
index b82cab2d97e..17f6a631ad8 100644
--- a/contrib/pg_freespacemap/pg_freespacemap.c
+++ b/contrib/pg_freespacemap/pg_freespacemap.c
@@ -9,8 +9,12 @@
#include "postgres.h"
#include "access/relation.h"
+#include "access/xloginsert.h"
+#include "catalog/storage_xlog.h"
#include "funcapi.h"
#include "storage/freespace.h"
+#include "storage/smgr.h"
+#include "utils/rel.h"
PG_MODULE_MAGIC;
@@ -20,6 +24,9 @@ PG_MODULE_MAGIC;
*/
PG_FUNCTION_INFO_V1(pg_freespace);
+/* Truncate the free space map, in case of corruption */
+PG_FUNCTION_INFO_V1(pg_truncate_freespace_map);
+
Datum
pg_freespace(PG_FUNCTION_ARGS)
{
@@ -40,3 +47,54 @@ pg_freespace(PG_FUNCTION_ARGS)
relation_close(rel, AccessShareLock);
PG_RETURN_INT16(freespace);
}
+
+
+Datum
+pg_truncate_freespace_map(PG_FUNCTION_ARGS)
+{
+ Oid relid = PG_GETARG_OID(0);
+ Relation rel;
+ ForkNumber fork;
+ BlockNumber block;
+
+ rel = relation_open(relid, AccessExclusiveLock);
+
+ /* Only some relkinds have a freespacemap */
+ if (!RELKIND_HAS_TABLE_AM(rel->rd_rel->relkind))
+ ereport(ERROR,
+ (errcode(ERRCODE_WRONG_OBJECT_TYPE),
+ errmsg("relation \"%s\" is of wrong relation kind",
+ RelationGetRelationName(rel)),
+ errdetail_relkind_not_supported(rel->rd_rel->relkind)));
+
+
+ /* Forcibly reset cached file size */
+ RelationGetSmgr(rel)->smgr_cached_nblocks[FSM_FORKNUM] = InvalidBlockNumber;
+
+ /* Just pretend we're going to wipeout the whole rel */
+ block = FreeSpaceMapPrepareTruncateRel(rel, 0);
+
+ if (BlockNumberIsValid(block))
+ {
+ fork = FSM_FORKNUM;
+ smgrtruncate(RelationGetSmgr(rel), &fork, 1, &block);
+ }
+
+ if (RelationNeedsWAL(rel))
+ {
+ xl_smgr_truncate xlrec;
+
+ xlrec.blkno = 0;
+ xlrec.rlocator = rel->rd_locator;
+ xlrec.flags = SMGR_TRUNCATE_FSM;
+
+ XLogBeginInsert();
+ XLogRegisterData((char *) &xlrec, sizeof(xlrec));
+
+ XLogInsert(RM_SMGR_ID, XLOG_SMGR_TRUNCATE | XLR_SPECIAL_REL_UPDATE);
+ }
+
+ relation_close(rel, AccessExclusiveLock);
+
+ PG_RETURN_VOID();
+}
diff --git a/contrib/pg_freespacemap/pg_freespacemap.control b/contrib/pg_freespacemap/pg_freespacemap.control
index ac8fc5050a9..1992320691b 100644
--- a/contrib/pg_freespacemap/pg_freespacemap.control
+++ b/contrib/pg_freespacemap/pg_freespacemap.control
@@ -1,5 +1,5 @@
# pg_freespacemap extension
comment = 'examine the free space map (FSM)'
-default_version = '1.2'
+default_version = '1.3'
module_pathname = '$libdir/pg_freespacemap'
relocatable = true
--
2.43.2
