Incident brief
Active SQL transaction
VACUUM (and a few other commands) refuse to run while a transaction block is still open. PostgreSQL rejected the command instead of running it partway.
In 10 seconds
- What
- Active SQL transaction
- What triggers it
- BEGIN a transaction.
- The fix
- Run VACUUM on its own, outside any BEGIN/COMMIT block (plain autocommit mode).
- Proof
- Reproduced on PostgreSQL 16.14 → Running VACUUM inside an open transaction was rejected with SQLSTATE 25001. The session was unaffected afterward.
The fix
What to do right now
The immediate, application-level response to this error.
- Run VACUUM on its own, outside any BEGIN/COMMIT block (plain autocommit mode).
- The same restriction applies to other commands too, such as CREATE DATABASE — see the premium test.
- Wrapping VACUUM in a PL/pgSQL DO block does not get around the restriction — see the counterexample.
VACUUM;Diagnose
See it live on the server
Run these against the affected instance to confirm the diagnosis before you act.
Standard triage — not specific to this error
These are canonical PostgreSQL system-catalog queries, shown as SQL to run. No sample output is attached because this is general triage, not a captured lab transcript.This SQLSTATE does not have an error-specific live snapshot yet. These are the canonical system-catalog queries you run against the affected server to see the problem in real time — standard triage, not a reproduced transcript.
What is running right now
Active backends, how long each has been running, and what it is waiting on.
SELECT pid,
state,
wait_event_type,
wait_event,
now() - query_start AS running_for,
left(query, 80) AS query
FROM pg_stat_activity
WHERE state <> 'idle'
AND pid <> pg_backend_pid()
ORDER BY running_for DESC NULLS LAST;Who is blocking whom
Turn raw blocking PIDs into the actual queries on both sides of the wait.
SELECT blocked.pid AS blocked_pid,
blocked.query AS blocked_query,
blocking.pid AS blocking_pid,
blocking.query AS blocking_query
FROM pg_stat_activity AS blocked
JOIN LATERAL unnest(pg_blocking_pids(blocked.pid)) AS b(pid) ON true
JOIN pg_stat_activity AS blocking ON blocking.pid = b.pid
WHERE cardinality(pg_blocking_pids(blocked.pid)) > 0;Locks that are still waiting
Every lock a backend has requested but not yet been granted.
SELECT l.pid,
l.locktype,
l.mode,
l.granted,
COALESCE(c.relname, l.transactionid::text) AS object
FROM pg_locks l
LEFT JOIN pg_class c ON c.oid = l.relation
WHERE NOT l.granted
ORDER BY l.pid;Why it happens
What PostgreSQL is telling you
The mechanism behind the error, grounded in the official manual — not paraphrased.
PostgreSQL 16 Documentation — VACUUM
VACUUM cannot be executed inside a transaction block.Read the full section on postgresql.org →
The blocked VACUUM
Per the manual, VACUUM cannot be executed inside a transaction block — it needs to run and finish on its own, outside any surrounding BEGIN/COMMIT.Confirming the session still works
The blocked VACUUM didn't affect the session — the next statement ran normally.Reproduce & verify
A real, single-session PostgreSQL reproduction
A literal transcript of SQL run against a live PostgreSQL instance in an isolated lab — the commands below are exactly what was executed.
- 1BEGIN a transaction.
- 2Run VACUUM inside it.
- 3SQLSTATE 25001 is reported; the transaction is aborted.
One client: open a transaction, then run VACUUM inside it.
-- No table needed: the restriction applies at the transaction-block level, not to a specific table.
SELECT 'no schema required' AS setup_note;BEGIN;
VACUUM;
ROLLBACK;SELECT 1 AS session_still_alive;What PostgreSQL actually returned
setup_note
--------------------
no schema required
(1 row)BEGIN
ERROR: VACUUM cannot run inside a transaction block
ROLLBACK session_still_alive
----------------------
1
(1 row)The manual's transaction-block restriction isn't unique to VACUUM. This was tested directly: CREATE DATABASE, a completely different command, run inside the same kind of open transaction.
Run CREATE DATABASE inside an open transaction, to see whether it shares VACUUM's rejection.
Without this
Above: VACUUM inside a transaction block is rejected with SQLSTATE 25001.
With this, tested
Below: CREATE DATABASE inside the same kind of open transaction is rejected with the very same SQLSTATE.
What Pro unlocks here
- The exact prevention SQL — copy-paste ready
- Raw psql output captured from the Docker lab
- A senior-DBA action list to take it further
- Live monitoring queries to catch it in production
- The deeper audit: fix-that-fails counterexample, GUC before/after, server-log evidence
Related & next steps
Follow the thread
Everything this error touches — jump straight to the sibling error, term, runbook, or parameter.
Verification
- Last verified
- 2026-07-16 (Docker lab, PostgreSQL 16.14)
- Reviewed by
- Verified against PostgreSQL 16.14 in an isolated lab environment
- Audit status
- reviewed