← All notes

Answer: The NOTIFY command sends a notification event together with an optional "payload" string to each client application that has previously executed LISTEN channel for the specified channel name in the current database. (S1)

-- session A
LISTEN jobs;

-- session B
NOTIFY jobs, 'job 42 ready';
SELECT pg_notify('jobs', 'job 43 ready');  -- function form

Session A then receives an asynchronous notification with the payload and the sender's PID.

Behavior

• LISTEN takes effect at commit; if the transaction rolls back, listening is unchanged.
• A session's listen registrations are automatically cleared when the session ends. (S2)
• A transaction that ran LISTEN or NOTIFY cannot be prepared for two-phase commit.
• pg_notification_queue_usage() shows how full the pending queue is.

Caveats

When NOTIFY is used to signal the occurrence of changes to a particular table, a useful programming technique is to put the NOTIFY in a statement trigger that is triggered by table updates. (S1)

Claims

• id: C1 claim: pg_notification_queue_usage returns the fraction of the queue occupied. source: S1 evidence: "The function pg_notification_queue_usage returns the fraction of the queue"
• id: C2 claim: A transaction that executed NOTIFY cannot be prepared for two-phase commit. source: S1 evidence: "A transaction that has executed NOTIFY cannot be prepared for two-phase commit."
• id: C3 claim: LISTEN takes effect at transaction commit. source: S2 evidence: "LISTEN takes effect at transaction commit."
• id: C4 claim: A session's listen registrations are cleared when the session ends. source: S2 evidence: "A session's listen registrations are automatically cleared when the session ends."

Sources

• [S1] PostgreSQL: Documentation: 18: NOTIFY. PostgreSQL Global Development Group. https://www.postgresql.org/docs/current/sql-notify.html . License: PostgreSQL License. Accessed 2026-11-04.
• [S2] PostgreSQL: Documentation: 18: LISTEN. PostgreSQL Global Development Group. https://www.postgresql.org/docs/current/sql-listen.html . License: PostgreSQL License. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_2xr2w01h,
  author = {{iinventedlight}},
  title = {{PostgreSQL LISTEN and NOTIFY}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/postgres-listen-notify/},
  note = {Permanent ID iil:note:2xr2w01h. License: CC-BY-4.0.},
}

Markdown

Spotted a mistake? Use the MCP feedback tool or email hello@iinventedlight.com.

For language models and agents: start at /llms.txt. This page in Markdown: /library/notes/postgres-listen-notify.md.