amcheck

functions for verifying relation integrity

https://www.postgresql.org/docs/current/amcheck.html

Overview

Package	Version	Category	License	Language
`amcheck`	`1.4`	ADMIN	PostgreSQL	C

ID	Extension	Bin	Lib	Load	Create	Trust	Reloc	Schema
5980	`amcheck`	No	Yes	No	Yes	No	No	-

Related	`pg_checksums` `pg_catcheck` `pg_orphaned` `pg_pathcheck` `pg_isok` `pg_surgery` `pageinspect` `adminpack` `pg_repack`

Version

PG18	PG17	PG16	PG15	PG14
1.4	1.4	1.4	1.4	1.4

Install

Note: This is a built-in contrib extension of PostgreSQL

CREATE EXTENSION amcheck;

Usage

amcheck: functions for verifying relation integrity

The amcheck extension provides functions to verify the logical consistency of B-tree indexes, GIN indexes, and heap (table) data, detecting corruption without modifying data.

B-Tree Index Verification

-- Lightweight check (AccessShareLock, safe for production)
SELECT bt_index_check('my_index');

-- With heap-all-indexed verification
SELECT bt_index_check('my_index', heapallindexed => true);

-- Thorough check including parent/child invariants (ShareLock, blocks writes)
SELECT bt_index_parent_check('my_index');

-- Most thorough: rootdescend re-finds each tuple from root
SELECT bt_index_parent_check('my_index',
    heapallindexed => true,
    rootdescend => true,
    checkunique => true);

Check All Catalog Indexes

SELECT bt_index_check(c.oid), c.relname, c.relpages
FROM pg_index i
JOIN pg_opclass op ON i.indclass[0] = op.oid
JOIN pg_am am ON op.opcmethod = am.oid
JOIN pg_class c ON i.indexrelid = c.oid
JOIN pg_namespace n ON c.relnamespace = n.oid
WHERE am.amname = 'btree' AND n.nspname = 'pg_catalog'
  AND c.relpersistence != 't' AND c.relkind = 'i'
  AND i.indisready AND i.indisvalid
ORDER BY c.relpages DESC LIMIT 10;

GIN Index Verification

SELECT gin_index_check('my_gin_index');

Heap (Table) Verification

-- Basic heap check
SELECT * FROM verify_heapam('my_table');

-- With TOAST verification (slower)
SELECT * FROM verify_heapam('my_table', check_toast => true);

-- Check specific block range
SELECT * FROM verify_heapam('my_table', startblock => 0, endblock => 1000);

-- Stop at first corrupted block
SELECT * FROM verify_heapam('my_table', on_error_stop => true);

Returns rows for each detected problem:

Column	Type	Description
`blkno`	bigint	Block number with corruption
`offnum`	integer	Offset of corrupt tuple
`attnum`	integer	Attribute number (if column-specific)
`msg`	text	Description of the problem

Function Summary

Function	Lock	Use Case
`bt_index_check(index, heapallindexed, checkunique)`	AccessShareLock	Routine production checks
`bt_index_parent_check(index, heapallindexed, rootdescend, checkunique)`	ShareLock	Comprehensive verification
`gin_index_check(index)`	AccessShareLock	GIN index verification
`verify_heapam(relation, on_error_stop, check_toast, skip, startblock, endblock)`	AccessShareLock	Table/heap corruption detection

All amcheck errors are true positives. Use REINDEX or point-in-time recovery for repair after diagnosing with pageinspect.