logical_decoding_work_mem

For DBAs and operators

One buffer per decoding walsender (or pg_logical_slot_get_changes() call), so it is safe to set well above work_mem: 256 MB–1 GB is common for systems with large batch transactions. Since PostgreSQL 14, a subscription with streaming = on (or parallel, PostgreSQL 16+; the default for new subscriptions is parallel since PostgreSQL 18) receives large in-progress transactions instead of the publisher spilling them.

Observe

SELECT slot_name, spill_txns, spill_count,
       pg_size_pretty(spill_bytes) AS spilled,
       stream_txns, pg_size_pretty(stream_bytes) AS streamed
  FROM pg_stat_replication_slots;

Spilling writes xid-*.spill files in pg_replslot/<slot>/; large values there plus replication lag point at this setting. Many subtransactions (e.g. PL/pgSQL exception blocks in a big batch) make decoding much more memory- and CPU-hungry. The limit counts only change data, not the reorder buffer's overhead, so actual memory can exceed it somewhat.

How to change it

Any user can change it for their session with SET.