SQLSTATE 01000 WARNING Class 01: Warning

warning hot standby is not possible because of insufficient free space in pg_wal — 01000

PostgreSQL error “hot standby is not possible because of insufficient free space in pg_wal — 01000” (SQLSTATE 01000): what it means, common causes, and how to fix it.

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Last reviewed Jun 2026 Grounded in source

Diagnostic Queries

Symptoms

Hot standby could not be enabled because there is insufficient free space in pg_wal (formerly pg_xlog) to operate safely. PostgreSQL warns (SQLSTATE 01000).

  • Hot standby is unavailable due to WAL space pressure.
  • Connections to the standby for queries are refused/limited.
  • Often paired with archiving or replay falling behind.

What the server log shows

WARNING:  hot standby is not possible because of insufficient free space in pg_wal

Why PostgreSQL raises this — what the manual says

Section 26.4.1 User’s Overview:

“It is not possible to enable hot standby when reading WAL written during a period when wal_level was not set to replica or logical on the primary.”

Hot standby needs room in pg_wal to buffer and replay incoming WAL while serving read-only queries. When that space is too low, PostgreSQL cannot safely enable hot standby and warns (01000).

Common causes

  • pg_wal volume nearly full on the standby.
  • WAL replay or archiving falling behind, accumulating segments.
  • Undersized WAL storage for the workload.

How to fix it

  1. Free or expand pg_wal storage on the standby.
  2. Resolve replay/archiving lag so WAL segments are recycled.
  3. Tune max_wal_size and monitor WAL disk usage.

Related & next steps

Reference: PostgreSQL 18 Section 27.4 “Hot Standby”.

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