Extensions
pg_visibility

pg_visibility

pg_visibility : examine the visibility map (VM) and page-level visibility info

Overview

ID Extension Package Version Category License Language
6960
pg_visibility
pg_visibility
 1.2
STAT
PostgreSQL
C
Attribute Has Binary Has Library Need Load Has DDL Relocatable Trusted
--s-d--
No
Yes
No
Yes
no
no
Relationships
See Also
amcheck
pageinspect
pg_freespacemap
pgstattuple
pgfincore
pg_checksums
pg_catcheck
pgcozy

Packages

PG18 PG17 PG16 PG15 PG14
1.2
1.2
1.2
1.2
1.2

This is a built-in contrib extension ship with the PostgreSQL kernel

Install

Create this extension with:

CREATE EXTENSION pg_visibility;

Usage

pg_visibility: examine the visibility map

pg_visibility provides functions to examine and verify the visibility map (VM), which tracks which pages contain only tuples visible to all transactions.

Functions

Single page visibility:

-- VM bits for a specific block
SELECT * FROM pg_visibility_map('my_table', 0);
-- Returns: all_visible, all_frozen

-- VM bits plus the page's PD_ALL_VISIBLE flag
SELECT * FROM pg_visibility('my_table', 0);
-- Returns: all_visible, all_frozen, pd_all_visible

All pages visibility:

-- VM bits for every page
SELECT * FROM pg_visibility_map('my_table');
-- Returns: blkno, all_visible, all_frozen

-- VM bits plus PD_ALL_VISIBLE for every page
SELECT * FROM pg_visibility('my_table');
-- Returns: blkno, all_visible, all_frozen, pd_all_visible

Summary:

SELECT * FROM pg_visibility_map_summary('my_table');
-- Returns: all_visible (count), all_frozen (count)

Corruption Detection 

-- Find tuples on all-frozen pages that aren't actually frozen
SELECT * FROM pg_check_frozen('my_table');

-- Find tuples on all-visible pages that aren't actually all-visible
SELECT * FROM pg_check_visible('my_table');

If either function returns rows, the visibility map is corrupt.

Repair 

-- Truncate the visibility map (forces full VACUUM rebuild)
SELECT pg_truncate_visibility_map('my_table');
-- Then run: VACUUM my_table;

Access

Functions require superuser or pg_stat_scan_tables role. pg_truncate_visibility_map requires superuser.

Last updated on
pg_freespacemappgstattuple