Database New Added 30 August 2026

PostgreSQL: canceling statement due to lock timeout

The statement waited longer than lock_timeout for a lock another transaction held. This is usually a migration queuing behind a long-running query, and the cancellation is protecting you from an unbounded stall.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

-- Who is holding it
SELECT pid, state, wait_event_type, left(query, 80)
FROM pg_stat_activity WHERE state <> 'idle' ORDER BY query_start;

-- Safer migration pattern: fail fast and retry
SET lock_timeout = '3s';
ALTER TABLE orders ADD COLUMN note text;

-- Avoid the lock entirely where possible
CREATE INDEX CONCURRENTLY idx_orders_note ON orders (note);

How to diagnose Database errors

Database errors group into connection exhaustion, lock contention and deadlocks, constraint violations, and resource limits. Connection errors under load are the most misdiagnosed: "too many connections" is almost never fixed by raising max_connections, because each connection costs memory. It is fixed by putting a pooler in front and finding the code path that leaks connections.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Look at what the server currently sees: SELECT * FROM pg_stat_activity in PostgreSQL, SHOW FULL PROCESSLIST in MySQL. Sessions sitting in idle in transaction are the usual culprit behind connection exhaustion.
For deadlocks, read the deadlock report the database logs. It names both transactions and the exact lock order. The fix is nearly always to make all code paths acquire locks in the same order.
Check whether the error is from the database or from a pooler. PgBouncer, ProxySQL and RDS Proxy return their own errors that look database-native but need pooler-side fixes.
Run EXPLAIN (ANALYZE, BUFFERS) on slow queries. Lock-wait timeouts are often just very slow queries holding locks longer than they should.
Verify you are connected to the writer, not a read replica. READONLY and "cannot execute in a read-only transaction" errors mean traffic is reaching the wrong endpoint.

Tools worth reaching for

pg_stat_activity
SHOW ENGINE INNODB STATUS
EXPLAIN ANALYZE
slow query log
pgbadger

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

postgresql.org

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