Functions and algorithms¶

New to the extension? Read Getting started and Concepts first. This page is the exhaustive reference.

Quick reference¶

Level	Generic API (optional)	Default 32-bit API
Page	—	`pg_page_checksum(regclass, integer)`
Cell	`pg_cell_checksum(regclass, tid, integer, text)`	`pg_cell_checksum(regclass, tid, integer)`
Tuple physical	`pg_tuple_physical_checksum(regclass, tid, boolean, text)`	`pg_tuple_physical_checksum(regclass, tid, boolean)`
Tuple logical	`pg_tuple_logical_checksum(regclass, tid, text)`	`pg_tuple_logical_checksum(regclass, tid)`
Table physical	`pg_table_physical_checksum(regclass, boolean, text)`	`pg_table_physical_checksum(regclass, boolean)`
Table logical	`pg_table_logical_checksum(regclass, text)`	`pg_table_logical_checksum(regclass)`
Index physical	`pg_index_physical_checksum(regclass, text)`	`pg_index_physical_checksum(regclass)`
Index logical	`pg_index_logical_checksum(regclass, text)`	`pg_index_logical_checksum(regclass)`
Database physical	`pg_database_physical_checksum(boolean, boolean, text)`	`pg_database_physical_checksum(boolean, boolean)`
Database logical	`pg_database_logical_checksum(boolean, boolean, text)`	`pg_database_logical_checksum(boolean, boolean)`
Data/text	`pg_data_checksum(bytea, bigint, text)` / `pg_text_checksum(text, bigint, text)`	`pg_data_checksum(bytea, integer)` / `pg_text_checksum(text, integer)`

The generic API returns bytea and accepts fnv32 or fnv64. The default 32-bit API returns integer/bigint and is the simplest choice for most users.

Privileges, NULL handling and object-level behavior are the same for the two forms. For per-function details, read the corresponding 32-bit function above; only the return type and algorithm argument differ.

Default 32-bit API and page checksums¶

The functions in this section return integer or bigint and use FNV-1a 32-bit. This is the simplest API and the default for most users. pg_page_checksum is the page API: PostgreSQL page checksums are always 32-bit.

Page Level Functions (Physical Only)¶

pg_page_checksum(regclass, integer) -> integer

Computes PostgreSQL's built-in page checksum for physical page corruption detection. The block number is validated: an out-of-range block (including -1, which would otherwise be interpreted as P_NEW) raises an error instead of reading or extending the relation. The page is copied before the checksum is computed, so the shared buffer is never modified.

-- Get checksum for page 5 of a table
SELECT pg_page_checksum('my_table'::regclass, 5);

Cell Level Functions (Logical Only)¶

pg_cell_checksum(regclass, tid, integer) -> integer

Computes logical checksum of a cell value. NULL values return CHECKSUM_NULL (-1). Requires SELECT on the relation; an out-of-range TID or attribute number returns NULL. Relations protected by row-level security are rejected.

-- Get checksum for cell (column) 3 of a specific tuple
SELECT pg_cell_checksum('employees'::regclass, '(5,2)'::tid, 3);

Note: Cell checksums are computed for individual values within specific rows, not for entire columns. To compute checksums for all values in a column, you would need to aggregate individual checksums.

Tuple Level Functions¶

pg_tuple_physical_checksum(regclass, tid, boolean) -> integer

Computes physical tuple checksum based on physical location (block, offset). Requires SELECT on the relation. An invalid TID returns NULL; a corrupted line pointer or tuple header raises a clean DATA_CORRUPTED error.

-- Physical checksum without header
SELECT pg_tuple_physical_checksum('orders'::regclass, ctid, false) 
FROM orders WHERE order_id = 123;

-- Physical checksum with header (includes MVCC info)
SELECT pg_tuple_physical_checksum('orders'::regclass, ctid, true) 
FROM orders WHERE order_id = 123;

pg_tuple_logical_checksum(regclass, tid) -> integer

Computes a canonical logical checksum of one row. All non-dropped columns are hashed; relation OIDs, heap TIDs and the tuple header are excluded. No primary key is required. Requires SELECT; relations protected by row-level security are rejected.

-- Logical checksum of one row
SELECT pg_tuple_logical_checksum('customers'::regclass, ctid)
FROM customers WHERE customer_id = 456;

Table Level Functions¶

pg_table_physical_checksum(regclass, boolean) -> bigint

Aggregates physical tuple checksums for entire table (order-independent). Requires SELECT on the table. The function accepts ordinary tables, materialized views, partitioned tables and (for physical checksums) TOAST relations. A TOAST relation is checksummed as raw pages, because its tuples are not heap tuples. A corrupted page produces a clean error rather than crashing the backend.

For an ordinary table, the physical checksum covers the main heap only: a TOAST value is represented by its pointer in the main tuple, so corruption inside the TOAST data is not detected by this function. Use pg_table_logical_checksum (which detoasts values) or a database physical checksum with include_toast = true to cover TOAST content.

-- Table physical checksum
SELECT pg_table_physical_checksum('inventory'::regclass, false);

-- With tuple headers included
SELECT pg_table_physical_checksum('inventory'::regclass, true);

pg_table_logical_checksum(regclass) -> bigint

Aggregates canonical logical row checksums for an entire table. It does not require a primary key, and relation OIDs are not included. Duplicate rows are preserved by a sum-plus-count aggregate, so two identical rows contribute twice. Requires SELECT on the table; returns NULL for a TOAST relation (toast content is covered when the parent table detoasts its values).

-- Logical checksum (no primary key required)
SELECT pg_table_logical_checksum('products'::regclass);

Partitioned tables: pg_table_physical_checksum and pg_table_logical_checksum accept partitioned tables. Since a partitioned table has no storage of its own, the extension recurses into every leaf partition. Logical checksums accumulate all leaf rows into the same accumulator, so the result does not depend on the partitioning layout. Nested (multi-level) partitioning is supported as well.

-- Checksum a partitioned table (recurses into all partitions)
SELECT pg_table_physical_checksum('sales'::regclass, false);
SELECT pg_table_logical_checksum('sales'::regclass);

Index Level Functions¶

pg_index_physical_checksum(regclass) -> integer

Computes physical checksum of index structure. Supports B-tree, Hash, GiST, GIN, SP-GiST, BRIN. Requires SELECT on the underlying table. Returns NULL for an unsupported access method. A partitioned index aggregates the physical checksums of its leaf indexes.

-- Physical checksum of a B-tree index
SELECT pg_index_physical_checksum('idx_product_name'::regclass);

pg_index_logical_checksum(regclass) -> integer

Computes the logical content of an index from the visible table rows and the index definition. Plain columns, expressions, partial-index predicates and INCLUDE columns are evaluated for each row; no heap TIDs, relation OIDs or dead entries are included. It works for every index access method (B-tree, Hash, GiST, GIN, SP-GiST, BRIN and custom AMs), and for partitioned indexes.

-- Logical content of any index
SELECT pg_index_logical_checksum('idx_product_name'::regclass);

Logical vs physical index checksums. The logical checksum describes what the index should contain from the table data; it does not inspect physical index pages. A missing or corrupt index entry is therefore detected by pg_index_physical_checksum, not by the logical value.

Database Level Functions (Superuser Only)¶

pg_database_physical_checksum(boolean, boolean) -> bigint

Aggregates physical relation checksums for entire database. Superuser-only; the check is enforced in C (the SQL functions are security invoker, so superuser() sees the calling session user).

-- Database physical checksum (excluding system tables)
SELECT pg_database_physical_checksum(false, false);

-- Include system catalogs and TOAST tables
SELECT pg_database_physical_checksum(true, true);

TOAST: include_toast is independent of include_system. With include_toast = true, TOAST relations are hashed as raw pages. With include_toast = false (the default), changes inside toasted values are not covered by the physical database checksum; table-level physical checksums store only the toast pointer in the main tuple.

Note about shared system tables: The database checksum only includes relations from the current database. Cluster-wide shared catalogs (e.g., pg_authid, pg_database) are excluded even when include_system is true.

Skipped relations: if a relation cannot be processed (dropped concurrently, corrupt, unsupported, ...), the scan rolls back an internal subtransaction, emits a warning and continues. A summary warning is emitted at the end. Cancellation and statement_timeout are propagated, so a canceled scan never returns a partial result as if it were complete.

PostgreSQL 12-16 and parallel database scans: those releases prohibit internal subtransactions while in parallel mode. A parallel database scan therefore cannot isolate relation errors: if a relation fails, the scan is aborted. Run with pg_integrity_checksums.workers = 0 (the default) to get the skip-with-warning behavior on PostgreSQL 12-16. Serial scans and parallel scans on PostgreSQL 17+ isolate errors as described above.

pg_database_logical_checksum(include_system boolean, include_indexes boolean) -> bigint

Aggregates canonical logical checksums for the database. Tables without a primary key are included. TOAST relations are skipped: their content is covered when the parent table detoasts the values. include_indexes (default true) controls whether logical index checksums are included; because they are derived from table data, they do not change when dead index entries are vacuumed.

Superuser-only (enforced in C).

-- Database logical checksum, including indexes
SELECT pg_database_logical_checksum(false, true);

-- Tables only
SELECT pg_database_logical_checksum(false, false);

Utility Functions¶

pg_data_checksum(bytea, integer) -> integer

Generic checksum for arbitrary binary data using FNV-1a.

SELECT pg_data_checksum(E'\x01020304'::bytea, 0);

pg_text_checksum(text, integer) -> integer

Wrapper for text data checksum.

SELECT pg_text_checksum('sample text', 0);

Generic API (optional 32/64-bit)¶

The default numeric functions above keep their FNV-1a 32-bit return type. The generic overloads take an extra text algorithm argument and return a raw bytea digest:

pg_data_checksum(bytea, bigint, text)
pg_text_checksum(text, bigint, text)
pg_cell_checksum(regclass, tid, integer, text)
pg_tuple_physical_checksum(regclass, tid, boolean, text)
pg_tuple_logical_checksum(regclass, tid, text)
pg_table_physical_checksum(regclass, boolean, text)
pg_table_logical_checksum(regclass, text)
pg_index_physical_checksum(regclass, text)
pg_index_logical_checksum(regclass, text)
pg_database_physical_checksum(boolean, boolean, text)
pg_database_logical_checksum(boolean, boolean, text)

Supported algorithms:

fnv32 — 4-byte big-endian digest;
fnv64 — 8-byte big-endian digest.

Table and database physical checksums always return 8 bytes because relation identity is part of the value. Convert a digest to a signed SQL bigint with:

pg_checksum_bigint(bytea) -> bigint
pg_checksum_bigint(bytea, boolean) -> bigint

The second argument selects unsigned interpretation for 4-byte fnv32 digests. The one-argument form sign-extends 4-byte values, matching the integer functions. Use the unsigned form when comparing with default table logical checksums, which return a positive 32-bit value in a bigint.

SELECT encode(pg_table_logical_checksum('orders'::regclass, 'fnv64'), 'hex');
SELECT pg_checksum_bigint(pg_table_logical_checksum('orders'::regclass, 'fnv64'));

pg_page_checksum intentionally has no generic overload: page checksums are PostgreSQL's built-in 32-bit page checksum.

Algorithm Details¶

FNV-1a 32-bit and 64-bit¶

Default logical, cell, tuple, table, index and utility functions use the FNV-1a (Fowler-Noll-Vo) 32-bit hash. Generic overloads add the 64-bit variant. PostgreSQL's pg_page_checksum is computed with PostgreSQL's own page-checksum routine, which is based on a modified FNV-1a variant; it is not the same function as the logical checksum and is always 32-bit.

Algorithm:

hash = basis
for each byte in data:
    hash = hash ^ byte;
    hash = hash * prime;

Constants:

FNV_BASIS_32 = 2166136261U
FNV_PRIME_32 = 16777619U
FNV_BASIS_64 = 14695981039346656037
FNV_PRIME_64 = 1099511628211
CHECKSUM_NULL = 0xFFFFFFFF (signed -1, 32-bit path)

The 64-bit path uses UINT64_MAX as its NULL sentinel and a 64-bit final mix. All canonical value handling (types, arrays, ranges, numerics, endianness) is shared between the 32-bit and 64-bit paths.

Order-Independent Aggregation¶

Physical and index aggregates use XOR, which is commutative and associative and therefore independent of scan order and partition boundaries.

Logical table, index and database aggregates use a sum plus count instead. Addition is still order-independent, but the count preserves duplicate rows, which a pure XOR would cancel. Parallel workers combine their partial sums and counts before the final mix, so serial and parallel results are identical for both 32-bit and 64-bit algorithms.

Type-Specific Handling¶

Logical values use a canonical type-aware encoding:

Scalar types use their binary send function (network byte order), or the output function when no send function exists.
Enums are hashed by label, not by type OID.
numeric is normalized with numeric_normalize(), so 1.0 and 1.00 compare equal.
Arrays, composites, domains and ranges are traversed recursively, so embedded type OIDs are not part of the hash.
Fixed-width integers in array shape, composite counts and multirange counts are encoded in little-endian byte order, independent of the server's native endianness.
Floating point canonicalizes NaN and negative zero.

Performance Characteristics¶

Computational Complexity¶

Function	Complexity	Notes
`pg_cell_checksum`	O(1)	Single cell, minimal overhead
`pg_tuple_*_checksum`	O(tuple size)	Requires buffer lock
`pg_table_*_checksum`	O(rows × columns)	Order-independent aggregation
`pg_index_physical_checksum`	O(index size)	Bulk read strategy
`pg_index_logical_checksum`	O(table rows)	Scans heap rows, not index pages
`pg_database_*_checksum`	O(total DB size)	Periodic interrupt checks

Table, index, and database scans can be parallelized with pg_integrity_checksums.workers; the scan work is divided among the workers with linear speedup up to the point where the scan becomes I/O-bound.