v7-0001-Add-contrib-pg_surgery-to-perform-surgery-on-a-damag.patch

From 4615bd2356a8102fed3f71efeb7181f8857f04e6 Mon Sep 17 00:00:00 2001
From: ashu <ashutosh.sharma@enterprisedb.com>
Date: Fri, 21 Aug 2020 18:13:35 +0530
Subject: [PATCH] Add contrib/pg_surgery to perform surgery on a damaged heap
 table.

This contrib module basically adds a couple of functions named
heap_force_kill and heap_force_freeze that can be used in the scripts
to perform surgery on the damaged heap tables.

Ashutosh Sharma.
---
 contrib/Makefile                           |   1 +
 contrib/pg_surgery/Makefile                |  23 ++
 contrib/pg_surgery/expected/pg_surgery.out | 161 +++++++++++
 contrib/pg_surgery/heap_surgery.c          | 418 +++++++++++++++++++++++++++++
 contrib/pg_surgery/pg_surgery--1.0.sql     |  18 ++
 contrib/pg_surgery/pg_surgery.control      |   5 +
 contrib/pg_surgery/sql/pg_surgery.sql      |  89 ++++++
 doc/src/sgml/contrib.sgml                  |   1 +
 doc/src/sgml/filelist.sgml                 |   1 +
 doc/src/sgml/pgsurgery.sgml                | 136 ++++++++++
 10 files changed, 853 insertions(+)
 create mode 100644 contrib/pg_surgery/Makefile
 create mode 100644 contrib/pg_surgery/expected/pg_surgery.out
 create mode 100644 contrib/pg_surgery/heap_surgery.c
 create mode 100644 contrib/pg_surgery/pg_surgery--1.0.sql
 create mode 100644 contrib/pg_surgery/pg_surgery.control
 create mode 100644 contrib/pg_surgery/sql/pg_surgery.sql
 create mode 100644 doc/src/sgml/pgsurgery.sgml

diff --git a/contrib/Makefile b/contrib/Makefile
index 1846d41..c8d2a16 100644
--- a/contrib/Makefile
+++ b/contrib/Makefile
@@ -34,6 +34,7 @@ SUBDIRS = \
 		pg_prewarm	\
 		pg_standby	\
 		pg_stat_statements \
+		pg_surgery	\
 		pg_trgm		\
 		pgcrypto	\
 		pgrowlocks	\
diff --git a/contrib/pg_surgery/Makefile b/contrib/pg_surgery/Makefile
new file mode 100644
index 0000000..ecf2e20
--- /dev/null
+++ b/contrib/pg_surgery/Makefile
@@ -0,0 +1,23 @@
+# contrib/pg_surgery/Makefile
+
+MODULE_big = pg_surgery
+OBJS = \
+	$(WIN32RES) \
+	heap_surgery.o
+
+EXTENSION = pg_surgery
+DATA = pg_surgery--1.0.sql
+PGFILEDESC = "pg_surgery - perform surgery on a damaged relation"
+
+REGRESS = pg_surgery
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/pg_surgery
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/contrib/pg_surgery/expected/pg_surgery.out b/contrib/pg_surgery/expected/pg_surgery.out
new file mode 100644
index 0000000..9858de2
--- /dev/null
+++ b/contrib/pg_surgery/expected/pg_surgery.out
@@ -0,0 +1,161 @@
+create extension pg_surgery;
+--
+-- check that using heap_force_kill and heap_force_freeze functions with the
+-- supported relations passes.
+--
+-- normal heap table.
+begin;
+create table htab(a int);
+insert into htab values (100), (200), (300), (400), (500);
+select * from htab where xmin = 2;
+ a 
+---
+(0 rows)
+
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 4)']::tid[]);
+ heap_force_freeze 
+-------------------
+ 
+(1 row)
+
+select ctid, xmax from htab where xmin = 2;
+ ctid  | xmax 
+-------+------
+ (0,4) |    0
+(1 row)
+
+select heap_force_kill('htab'::regclass, ARRAY['(0, 4)']::tid[]);
+ heap_force_kill 
+-----------------
+ 
+(1 row)
+
+select * from htab where ctid = '(0, 4)';
+ a 
+---
+(0 rows)
+
+rollback;
+-- materialized view.
+begin;
+create materialized view mvw as select a from generate_series(1, 3) a;
+select * from mvw where xmin = 2;
+ a 
+---
+(0 rows)
+
+select heap_force_freeze('mvw'::regclass, ARRAY['(0, 3)']::tid[]);
+ heap_force_freeze 
+-------------------
+ 
+(1 row)
+
+select * from mvw where xmin = 2;
+ a 
+---
+ 3
+(1 row)
+
+select heap_force_kill('mvw'::regclass, ARRAY['(0, 3)']::tid[]);
+ heap_force_kill 
+-----------------
+ 
+(1 row)
+
+select * from mvw where ctid = '(0, 3)';
+ a 
+---
+(0 rows)
+
+rollback;
+--
+-- check that using heap_force_kill and heap_force_freeze functions with the
+-- unsupported relations fails.
+--
+-- partitioned tables (the parent table) doesn't contain any tuple.
+create table ptab (a int) partition by list (a);
+select heap_force_kill('ptab'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  only the relation using heap_tableam_handler is supported
+select heap_force_freeze('ptab'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  only the relation using heap_tableam_handler is supported
+create index ptab_idx on ptab (a);
+-- indexes are not supported, should fail.
+select heap_force_kill('ptab_idx'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  only the relation using heap_tableam_handler is supported
+select heap_force_freeze('ptab_idx'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  only the relation using heap_tableam_handler is supported
+create view vw as select 1;
+-- views are not supported as well. so, all these should fail.
+select heap_force_kill('vw'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  only the relation using heap_tableam_handler is supported
+select heap_force_freeze('vw'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  only the relation using heap_tableam_handler is supported
+create sequence seq;
+-- sequences are not supported as well. so, all these functions should fail.
+select heap_force_kill('seq'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  "seq" is not a table, materialized view, or TOAST table
+select heap_force_freeze('seq'::regclass, ARRAY['(0, 1)']::tid[]);
+ERROR:  "seq" is not a table, materialized view, or TOAST table
+--
+-- Some negative test-cases with invalid inputs.
+--
+begin;
+create table htab(a int);
+-- invalid block number, should be skipped.
+select heap_force_kill('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+NOTICE:  skipping block 0 for relation "htab" because the block number is out of range
+ heap_force_kill 
+-----------------
+ 
+(1 row)
+
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+NOTICE:  skipping block 0 for relation "htab" because the block number is out of range
+ heap_force_freeze 
+-------------------
+ 
+(1 row)
+
+insert into htab values (10);
+-- invalid offset number, should be skipped.
+select heap_force_kill('htab'::regclass, ARRAY['(0, 2)']::tid[]);
+NOTICE:  skipping tid (0, 2) for relation "htab" because the item number is out of range for this block
+ heap_force_kill 
+-----------------
+ 
+(1 row)
+
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 2)']::tid[]);
+NOTICE:  skipping tid (0, 2) for relation "htab" because the item number is out of range for this block
+ heap_force_freeze 
+-------------------
+ 
+(1 row)
+
+-- dead tuple, should be skipped.
+select heap_force_kill('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+ heap_force_kill 
+-----------------
+ 
+(1 row)
+
+select heap_force_kill('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+NOTICE:  skipping tid (0, 1) for relation "htab" because it is marked dead
+ heap_force_kill 
+-----------------
+ 
+(1 row)
+
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+NOTICE:  skipping tid (0, 1) for relation "htab" because it is marked dead
+ heap_force_freeze 
+-------------------
+ 
+(1 row)
+
+rollback;
+-- cleanup.
+drop table ptab;
+drop view vw;
+drop sequence seq;
+drop extension pg_surgery;
diff --git a/contrib/pg_surgery/heap_surgery.c b/contrib/pg_surgery/heap_surgery.c
new file mode 100644
index 0000000..5228990
--- /dev/null
+++ b/contrib/pg_surgery/heap_surgery.c
@@ -0,0 +1,418 @@
+/*-------------------------------------------------------------------------
+ *
+ * heap_surgery.c
+ *	  Functions to perform surgery on the damaged heap table.
+ *
+ * Copyright (c) 2020, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  contrib/pg_surgery/heap_surgery.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/heapam.h"
+#include "access/visibilitymap.h"
+#include "catalog/pg_am_d.h"
+#include "catalog/pg_proc_d.h"
+#include "miscadmin.h"
+#include "storage/bufmgr.h"
+#include "utils/acl.h"
+#include "utils/rel.h"
+
+PG_MODULE_MAGIC;
+
+/* Options to forcefully change the state of a heap tuple. */
+typedef enum HeapTupleForceOption
+{
+	HEAP_FORCE_KILL,
+	HEAP_FORCE_FREEZE
+} HeapTupleForceOption;
+
+PG_FUNCTION_INFO_V1(heap_force_kill);
+PG_FUNCTION_INFO_V1(heap_force_freeze);
+
+static int32 tidcmp(const void *a, const void *b);
+static Datum heap_force_common(FunctionCallInfo fcinfo,
+							   HeapTupleForceOption heap_force_opt);
+static void sanity_check_tid_array(ArrayType *ta, int *ntids);
+static void sanity_check_relation(Relation rel);
+static BlockNumber tids_same_page_fetch_offnums(ItemPointer tids, int ntids,
+												OffsetNumber *next_start_ptr,
+												OffsetNumber *offnos);
+
+/*-------------------------------------------------------------------------
+ * heap_force_kill()
+ *
+ * Force kill the tuple(s) pointed to by the item pointer(s) stored in the
+ * given tid array.
+ *
+ * Usage: SELECT heap_force_kill(regclass, tid[]);
+ *-------------------------------------------------------------------------
+ */
+Datum
+heap_force_kill(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_DATUM(heap_force_common(fcinfo, HEAP_FORCE_KILL));
+}
+
+/*-------------------------------------------------------------------------
+ * heap_force_freeze()
+ *
+ * Force freeze the tuple(s) pointed to by the item pointer(s) stored in the
+ * given tid array.
+ *
+ * Usage: SELECT heap_force_freeze(regclass, tid[]);
+ *-------------------------------------------------------------------------
+ */
+Datum
+heap_force_freeze(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_DATUM(heap_force_common(fcinfo, HEAP_FORCE_FREEZE));
+}
+
+/*-------------------------------------------------------------------------
+ * heap_force_common()
+ *
+ * Common code for heap_force_kill and heap_force_freeze
+ *-------------------------------------------------------------------------
+ */
+static Datum
+heap_force_common(FunctionCallInfo fcinfo, HeapTupleForceOption heap_force_opt)
+{
+	Oid				relid = PG_GETARG_OID(0);
+	ArrayType	   *ta = PG_GETARG_ARRAYTYPE_P_COPY(1);
+	ItemPointer		tids;
+	int				ntids,
+					nblocks;
+	Relation		rel;
+	OffsetNumber   *offnos;
+	OffsetNumber	noffs,
+					curr_start_ptr,
+					next_start_ptr;
+
+	if (RecoveryInProgress())
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("recovery is in progress"),
+				 errhint("heap surgery functions cannot be executed during recovery.")));
+
+	/* Basic sanity checking. */
+	sanity_check_tid_array(ta, &ntids);
+
+	rel = relation_open(relid, RowExclusiveLock);
+
+	sanity_check_relation(rel);
+
+	tids = ((ItemPointer) ARR_DATA_PTR(ta));
+
+	/*
+	 * If there is more than one tid in the array, sort it so that we can
+	 * easily fetch all the tids belonging to one particular page from the
+	 * array.
+	 */
+	if (ntids > 1)
+		qsort((void*) tids, ntids, sizeof(ItemPointerData), tidcmp);
+
+	offnos = (OffsetNumber *) palloc(ntids * sizeof(OffsetNumber));
+	noffs = curr_start_ptr = next_start_ptr = 0;
+	nblocks = RelationGetNumberOfBlocks(rel);
+
+	do
+	{
+		Buffer			buf;
+		Buffer			vmbuf = InvalidBuffer;
+		Page			page;
+		BlockNumber		blkno;
+		OffsetNumber	maxoffset;
+		int				i;
+		bool			did_modify_page = false;
+		bool			did_modify_vm = false;
+
+		/*
+		 * Get the offset numbers from the tids belonging to one particular page
+		 * and process them one by one.
+		 */
+		blkno = tids_same_page_fetch_offnums(tids, ntids, &next_start_ptr,
+											 offnos);
+
+		/* Calculate the number of offsets stored in offnos array. */
+		noffs = next_start_ptr - curr_start_ptr;
+
+		/*
+		 * Update the current start pointer so that next time when
+		 * tids_same_page_fetch_offnums() is called, we can calculate the number
+		 * of offsets present in the offnos array.
+		 */
+		curr_start_ptr = next_start_ptr;
+
+		/* Check whether the block number is valid. */
+		if (blkno >= nblocks)
+		{
+			ereport(NOTICE,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("skipping block %u for relation \"%s\" because the block number is out of range",
+							blkno, RelationGetRelationName(rel))));
+			continue;
+		}
+
+		CHECK_FOR_INTERRUPTS();
+
+		buf = ReadBuffer(rel, blkno);
+		LockBufferForCleanup(buf);
+
+		page = BufferGetPage(buf);
+
+		maxoffset = PageGetMaxOffsetNumber(page);
+
+		/*
+		 * Before entering the critical section, pin the visibility map page if
+		 * it appears to be necessary.
+		 */
+		if (heap_force_opt == HEAP_FORCE_KILL && PageIsAllVisible(page))
+			visibilitymap_pin(rel, blkno, &vmbuf);
+
+		/* No ereport(ERROR) from here until all the changes are logged. */
+		START_CRIT_SECTION();
+
+		for (i = 0; i < noffs; i++)
+		{
+			OffsetNumber	offno;
+			ItemId			itemid;
+
+			if (offnos[i] == 0 || offnos[i] > maxoffset)
+			{
+				ereport(NOTICE,
+						 errmsg("skipping tid (%u, %u) for relation \"%s\" because the item number is out of range for this block",
+								blkno, offnos[i], RelationGetRelationName(rel)));
+				continue;
+			}
+
+			itemid = PageGetItemId(page, offnos[i]);
+
+			/* Follow any redirections until we find something useful. */
+			while (ItemIdIsRedirected(itemid))
+			{
+				offno = ItemIdGetRedirect(itemid);
+				itemid = PageGetItemId(page, offno);
+				CHECK_FOR_INTERRUPTS();
+			}
+
+			/* Nothing to do if the itemid is unused or already dead. */
+			if (!ItemIdIsUsed(itemid) || ItemIdIsDead(itemid))
+			{
+				if (!ItemIdIsUsed(itemid))
+					ereport(NOTICE,
+							(errmsg("skipping tid (%u, %u) for relation \"%s\" because it is marked unused",
+									blkno, offnos[i], RelationGetRelationName(rel))));
+				else
+					ereport(NOTICE,
+							(errmsg("skipping tid (%u, %u) for relation \"%s\" because it is marked dead",
+									blkno, offnos[i], RelationGetRelationName(rel))));
+				continue;
+			}
+
+			Assert(ItemIdIsNormal(itemid));
+
+			did_modify_page = true;
+
+			if (heap_force_opt == HEAP_FORCE_KILL)
+			{
+
+				ItemIdSetDead(itemid);
+
+				/*
+				 * If the page is marked all-visible, we must clear
+				 * PD_ALL_VISIBLE flag on the page header and an all-visible bit
+				 * on the visibility map corresponding to the page.
+				 */
+				if (PageIsAllVisible(page))
+				{
+					PageClearAllVisible(page);
+					visibilitymap_clear(rel, blkno, vmbuf,
+										VISIBILITYMAP_ALL_VISIBLE);
+					did_modify_vm = true;
+				}
+			}
+			else
+			{
+				HeapTupleHeader	htup;
+				ItemPointerData	ctid;
+
+				Assert(heap_force_opt == HEAP_FORCE_FREEZE);
+
+				ItemPointerSet(&ctid, blkno, offnos[i]);
+
+				htup = (HeapTupleHeader) PageGetItem(page, itemid);
+
+				/*
+				 * Make sure that this tuple holds the correct item pointer
+				 * value.
+				 */
+				if (!ItemPointerEquals(&ctid, &htup->t_ctid))
+					ItemPointerSet(&htup->t_ctid, blkno, offnos[i]);
+
+				HeapTupleHeaderSetXmin(htup, FrozenTransactionId);
+				HeapTupleHeaderSetXmax(htup, InvalidTransactionId);
+
+				/* We might have MOVED_OFF/MOVED_IN tuples in the database */
+				if (htup->t_infomask & HEAP_MOVED)
+				{
+					if (htup->t_infomask & HEAP_MOVED_OFF)
+						HeapTupleHeaderSetXvac(htup, InvalidTransactionId);
+					else
+						HeapTupleHeaderSetXvac(htup, FrozenTransactionId);
+				}
+
+				/*
+				 * Clear all the visibility-related bits of this tuple and mark
+				 * it as frozen. Also, get rid of HOT_UPDATED and KEYS_UPDATES
+				 * bits.
+				 */
+				htup->t_infomask &= ~HEAP_XACT_MASK;
+				htup->t_infomask |= (HEAP_XMIN_FROZEN | HEAP_XMAX_INVALID);
+				htup->t_infomask2 &= ~HEAP_HOT_UPDATED;
+				htup->t_infomask2 &= ~HEAP_KEYS_UPDATED;
+			}
+		}
+
+		/*
+		 * If the page was modified, only then, we mark the buffer dirty or do
+		 * the WAL logging.
+		 */
+		if (did_modify_page)
+		{
+			/* Mark buffer dirty before we write WAL. */
+			MarkBufferDirty(buf);
+
+			/* XLOG stuff */
+			if (RelationNeedsWAL(rel))
+				log_newpage_buffer(buf, true);
+		}
+
+		/* WAL log the VM page if it was modified. */
+		if (did_modify_vm && RelationNeedsWAL(rel))
+			log_newpage_buffer(vmbuf, false);
+
+		END_CRIT_SECTION();
+
+		UnlockReleaseBuffer(buf);
+
+		if (vmbuf != InvalidBuffer)
+			ReleaseBuffer(vmbuf);
+	} while (next_start_ptr != ntids);
+
+	relation_close(rel, RowExclusiveLock);
+
+	pfree(ta);
+	pfree(offnos);
+
+	PG_RETURN_VOID();
+}
+
+/*-------------------------------------------------------------------------
+ * tidcmp()
+ *
+ * Compare two item pointers, return -1, 0, or +1.
+ *
+ * See ItemPointerCompare for details.
+ * ------------------------------------------------------------------------
+ */
+static int32
+tidcmp(const void *a, const void *b)
+{
+	ItemPointer iptr1 = ((const ItemPointer) a);
+	ItemPointer iptr2 = ((const ItemPointer) b);
+
+	return ItemPointerCompare(iptr1, iptr2);
+}
+
+/*-------------------------------------------------------------------------
+ * sanity_check_tid_array()
+ *
+ * Perform sanity check on the given tid array.
+ * ------------------------------------------------------------------------
+ */
+static void
+sanity_check_tid_array(ArrayType *ta, int *ntids)
+{
+	if (ARR_HASNULL(ta) && array_contains_nulls(ta))
+		ereport(ERROR,
+				(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+				 errmsg("array must not contain nulls")));
+
+	*ntids = ArrayGetNItems(ARR_NDIM(ta), ARR_DIMS(ta));
+
+	if (*ntids == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("empty tid array")));
+}
+
+/*-------------------------------------------------------------------------
+ * sanity_check_relation()
+ *
+ * Perform sanity check on the given relation.
+ * ------------------------------------------------------------------------
+ */
+static void
+sanity_check_relation(Relation rel)
+{
+	if (rel->rd_amhandler != HEAP_TABLE_AM_HANDLER_OID)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("only the relation using heap_tableam_handler is supported")));
+
+	if (rel->rd_rel->relkind != RELKIND_RELATION &&
+		rel->rd_rel->relkind != RELKIND_MATVIEW &&
+		rel->rd_rel->relkind != RELKIND_TOASTVALUE)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("\"%s\" is not a table, materialized view, or TOAST table",
+						RelationGetRelationName(rel))));
+
+	/* Must be owner of the table or superuser. */
+	if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
+		aclcheck_error(ACLCHECK_NOT_OWNER,
+					   get_relkind_objtype(rel->rd_rel->relkind),
+					   RelationGetRelationName(rel));
+}
+
+/*-------------------------------------------------------------------------
+ * tids_same_page_fetch_offnums()
+ *
+ * Find out all the tids residing in the same page as tids[next_start_ptr] and
+ * fetch the offset number stored in each of them into a caller-allocated offset
+ * number array.
+ * ------------------------------------------------------------------------
+ */
+static BlockNumber
+tids_same_page_fetch_offnums(ItemPointer tids, int ntids,
+							 OffsetNumber *next_start_ptr, OffsetNumber *offnos)
+{
+	int				i;
+	BlockNumber		prev_blkno,
+					blkno;
+	OffsetNumber	offno;
+
+	prev_blkno = blkno = InvalidBlockNumber;
+
+	for (i = *next_start_ptr; i < ntids; i++)
+	{
+		ItemPointerData tid = tids[i];
+
+		blkno = ItemPointerGetBlockNumberNoCheck(&tid);
+		offno = ItemPointerGetOffsetNumberNoCheck(&tid);
+
+		if (i == *next_start_ptr || (prev_blkno == blkno))
+			offnos[i - *next_start_ptr] = offno;
+		else
+			break;
+
+		prev_blkno = blkno;
+	}
+
+	*next_start_ptr = i;
+	return prev_blkno;
+}
\ No newline at end of file
diff --git a/contrib/pg_surgery/pg_surgery--1.0.sql b/contrib/pg_surgery/pg_surgery--1.0.sql
new file mode 100644
index 0000000..2ae7f22
--- /dev/null
+++ b/contrib/pg_surgery/pg_surgery--1.0.sql
@@ -0,0 +1,18 @@
+/* contrib/pg_surgery/pg_surgery--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION pg_surgery" to load this file. \quit
+
+CREATE FUNCTION heap_force_kill(reloid regclass, tids tid[])
+RETURNS VOID
+AS 'MODULE_PATHNAME', 'heap_force_kill'
+LANGUAGE C STRICT;
+
+REVOKE EXECUTE ON FUNCTION heap_force_kill(regclass, tid[]) FROM PUBLIC;
+
+CREATE FUNCTION heap_force_freeze(reloid regclass, tids tid[])
+RETURNS VOID
+AS 'MODULE_PATHNAME', 'heap_force_freeze'
+LANGUAGE C STRICT;
+
+REVOKE EXECUTE ON FUNCTION heap_force_freeze(regclass, tid[]) FROM PUBLIC;
\ No newline at end of file
diff --git a/contrib/pg_surgery/pg_surgery.control b/contrib/pg_surgery/pg_surgery.control
new file mode 100644
index 0000000..2bcdad1
--- /dev/null
+++ b/contrib/pg_surgery/pg_surgery.control
@@ -0,0 +1,5 @@
+# pg_surgery extension
+comment = 'extension to perform surgery on a damaged relation'
+default_version = '1.0'
+module_pathname = '$libdir/pg_surgery'
+relocatable = true
diff --git a/contrib/pg_surgery/sql/pg_surgery.sql b/contrib/pg_surgery/sql/pg_surgery.sql
new file mode 100644
index 0000000..4aef380
--- /dev/null
+++ b/contrib/pg_surgery/sql/pg_surgery.sql
@@ -0,0 +1,89 @@
+create extension pg_surgery;
+
+--
+-- check that using heap_force_kill and heap_force_freeze functions with the
+-- supported relations passes.
+--
+
+-- normal heap table.
+begin;
+create table htab(a int);
+insert into htab values (100), (200), (300), (400), (500);
+
+select * from htab where xmin = 2;
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 4)']::tid[]);
+select ctid, xmax from htab where xmin = 2;
+
+select heap_force_kill('htab'::regclass, ARRAY['(0, 4)']::tid[]);
+select * from htab where ctid = '(0, 4)';
+rollback;
+
+-- materialized view.
+begin;
+create materialized view mvw as select a from generate_series(1, 3) a;
+
+select * from mvw where xmin = 2;
+select heap_force_freeze('mvw'::regclass, ARRAY['(0, 3)']::tid[]);
+select * from mvw where xmin = 2;
+
+select heap_force_kill('mvw'::regclass, ARRAY['(0, 3)']::tid[]);
+select * from mvw where ctid = '(0, 3)';
+rollback;
+
+--
+-- check that using heap_force_kill and heap_force_freeze functions with the
+-- unsupported relations fails.
+--
+
+-- partitioned tables (the parent table) doesn't contain any tuple.
+create table ptab (a int) partition by list (a);
+
+select heap_force_kill('ptab'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_freeze('ptab'::regclass, ARRAY['(0, 1)']::tid[]);
+
+create index ptab_idx on ptab (a);
+
+-- indexes are not supported, should fail.
+select heap_force_kill('ptab_idx'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_freeze('ptab_idx'::regclass, ARRAY['(0, 1)']::tid[]);
+
+create view vw as select 1;
+
+-- views are not supported as well. so, all these should fail.
+select heap_force_kill('vw'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_freeze('vw'::regclass, ARRAY['(0, 1)']::tid[]);
+
+create sequence seq;
+
+-- sequences are not supported as well. so, all these functions should fail.
+select heap_force_kill('seq'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_freeze('seq'::regclass, ARRAY['(0, 1)']::tid[]);
+
+--
+-- Some negative test-cases with invalid inputs.
+--
+begin;
+create table htab(a int);
+
+-- invalid block number, should be skipped.
+select heap_force_kill('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+
+insert into htab values (10);
+
+-- invalid offset number, should be skipped.
+select heap_force_kill('htab'::regclass, ARRAY['(0, 2)']::tid[]);
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 2)']::tid[]);
+
+-- dead tuple, should be skipped.
+select heap_force_kill('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_kill('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+select heap_force_freeze('htab'::regclass, ARRAY['(0, 1)']::tid[]);
+
+rollback;
+
+-- cleanup.
+drop table ptab;
+drop view vw;
+drop sequence seq;
+drop extension pg_surgery;
diff --git a/doc/src/sgml/contrib.sgml b/doc/src/sgml/contrib.sgml
index 261a559..c82dde2 100644
--- a/doc/src/sgml/contrib.sgml
+++ b/doc/src/sgml/contrib.sgml
@@ -125,6 +125,7 @@ CREATE EXTENSION <replaceable>module_name</replaceable>;
  &pgrowlocks;
  &pgstatstatements;
  &pgstattuple;
+ &pgsurgery;
  &pgtrgm;
  &pgvisibility;
  &postgres-fdw;
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index 64b5da0..828396d 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -139,6 +139,7 @@
 <!ENTITY pgstandby       SYSTEM "pgstandby.sgml">
 <!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">
 <!ENTITY pgstattuple     SYSTEM "pgstattuple.sgml">
+<!ENTITY pgsurgery       SYSTEM "pgsurgery.sgml">
 <!ENTITY pgtrgm          SYSTEM "pgtrgm.sgml">
 <!ENTITY pgvisibility    SYSTEM "pgvisibility.sgml">
 <!ENTITY postgres-fdw    SYSTEM "postgres-fdw.sgml">
diff --git a/doc/src/sgml/pgsurgery.sgml b/doc/src/sgml/pgsurgery.sgml
new file mode 100644
index 0000000..8120c1b
--- /dev/null
+++ b/doc/src/sgml/pgsurgery.sgml
@@ -0,0 +1,136 @@
+<!-- doc/src/sgml/pgsurgery.sgml -->
+
+<sect1 id="pgsurgery" xreflabel="pg_surgery">
+ <title>pg_surgery</title>
+
+ <indexterm zone="pgsurgery">
+  <primary>pg_surgery</primary>
+ </indexterm>
+
+ <para>
+  The <filename>pg_surgery</filename> module provides various functions to
+  perform surgery on a damaged relation. It is intended to be used only with a
+  damaged relation and must be operated only on damaged tuples of such
+  relations.
+ </para>
+
+ <para>
+  By default, only the superusers have <literal>EXECUTE</literal> privilege on
+  the functions provided by this module. Once the extension has been installed,
+  users may issue <command>GRANT</command> commands to change the privileges on
+  the functions to allow others to execute them.
+ </para>
+
+ <note>
+ <para>
+  After a surgery is performed on a damaged relation using this module, we must
+  run VACUUM with DISABLE_PAGE_SKIPPING option on that relation to bring it back
+  into a sane state (see examples in the next section).
+ </para>
+ </note>
+
+ <note>
+ <para>
+  While performing surgery on a damaged relation, we must not be doing anything
+  else on that relation in parallel. This is to ensure that when we are
+  operating on a damaged tuple there is no other transaction trying to modify
+  that tuple.
+ </para>
+ </note>
+
+ <sect2>
+  <title>Functions</title>
+
+  <variablelist>
+   <varlistentry>
+    <term>
+     <function>heap_force_kill(regclass, tid[]) returns void</function>
+    </term>
+
+    <listitem>
+     <para>
+      <function>heap_force_kill</function> marks a <quote>used</quote> line
+      pointer as <quote>dead</quote> without examining the tuple. It is used to
+      force-kill a corrupted tuple in the table that may or may not be
+      accessible. It takes the relation oid and an array of item pointers as an
+      input arguments. Here is an example demonstrating when and how this
+      function is used:
+<programlisting>
+test=&gt; select * from t1 where ctid = '(0, 1)';
+ERROR:  could not access status of transaction 4007513275
+DETAIL:  Could not open file "pg_xact/0EED": No such file or directory.
+
+test=# select heap_force_kill('t1'::regclass, ARRAY['(0, 1)']::tid[]);
+-[ RECORD 1 ]---+-
+heap_force_kill |
+
+test=# vacuum (disable_page_skipping) t1;
+VACUUM 
+
+test=# select * from t1 where ctid = '(0, 1)';
+(0 rows)
+</programlisting>
+    </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term>
+     <function>heap_force_freeze(regclass, tid[]) returns void</function>
+    </term>
+
+    <listitem>
+     <para>
+      <function>heap_force_freeze</function> marks a live tuple (whose xmin is
+      corrupted) as frozen by setting its xmin to FrozenTransactionId and xmax
+      to InvalidTransactionId. It clears all the visibility related bits in the
+      infomask of the tuple and sets the infomask to HEAP_XMIN_FROZEN and
+      HEAP_XMAX_INVALID. It is used to force-freeze a tuple in the table for
+      which VACUUM fails with "found xmin ... from before relfrozenxid ..."
+      error. Similar to <function>heap_force_kill</function> function, this also
+      takes the relation oid and an array of item pointers as an input arguments.
+      Here is an example demonstrating when and how this function is used:
+<programlisting>
+test=&gt; vacuum t1;
+ERROR:  found xmin 507 from before relfrozenxid 515
+CONTEXT:  while scanning block 0 of relation "public.t1"
+
+test=# select ctid from t1 where xmin = 507;
+ ctid  
+-------
+ (0,3)
+(1 row)
+
+test=# select heap_force_freeze('t1'::regclass, ARRAY['(0, 3)']::tid[]);
+-[ RECORD 1 ]-----+-
+heap_force_freeze | 
+
+test=# vacuum (disable_page_skipping) t1;
+VACUUM
+</programlisting>
+    </para>
+
+    <note>
+    <para>
+     This function should only be operated on a tuple for which VACUUM fails
+     with "found xmin ... from before relfrozenxid ..." error. The user must
+     verify that only the xmin and ctid fields of the tuple are corrupted, if
+     any other fields of a tuple are corrupted, they must avoid running this
+     function on such tuples.
+    </para>
+    </note>
+   </listitem>
+  </varlistentry>
+
+  </variablelist>
+ </sect2>
+
+ <sect2>
+  <title>Authors</title>
+
+  <para>
+   Ashutosh Sharma <email>ashu.coek88@gmail.com</email>
+  </para>
+ </sect2>
+
+</sect1>
-- 
1.8.3.1