pg_wal_lsn_diff() — PostgreSQL system administration function

pg_wal_lsn_diff(): difference in bytes, given two wal locations. PostgreSQL system administration functions — signature, volatility, version applicability and an illustrative example.

The Sev-1 Admin
The Sev-1 Admin  ·  2 min read

Summary

pg_wal_lsn_diff is a PostgreSQL built-in function in the System Administration Functions group. PostgreSQL’s system catalog (pg_proc) describes it as: “difference in bytes, given two wal locations”.

Signature

pg_wal_lsn_diff(pg_lsn, pg_lsn) → numeric

Argument and return types are taken from the pg_proc catalog; internal type names are shown using their readable SQL spellings (for example int4 is shown as integer). (Derived from the catalog — see the linked reference for the canonical documentation.)

Classification

  • Category: System Administration Functions
  • Kind: Function
  • Volatility: IMMUTABLE — Marked IMMUTABLE — it always returns the same result for the same arguments and can be used in indexes and other contexts that require immutability.
  • Returns: numeric

Example

Illustrative form (replace placeholder values with your own data):

SELECT pg_wal_lsn_diff(NULL::pg_lsn, NULL::pg_lsn);

The example above is illustrative and is meant to show calling syntax only; consult the linked PostgreSQL documentation for exact semantics, edge cases and accepted argument combinations.

Version applicability

pg_wal_lsn_diff is present across the surveyed releases (PostgreSQL 15, 16, 17, 18, 19). On older major versions, behaviour may differ in detail — always check the documentation for the version you run.

Related & references

Reference: PostgreSQL documentation — System Administration Functions.