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Description

Error 55P03, 'lock not available', indicates that your PostgreSQL session or transaction failed to acquire a necessary lock on a database object. This typically occurs when another concurrent transaction already holds a conflicting lock, preventing your operation from proceeding immediately.

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Error Message

lock not available

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Known Causes

3 known causes

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Conflicting Concurrent Transactions

Another active database session or transaction is currently holding a conflicting lock on the requested resource, preventing your operation from acquiring it.

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Long-Running Transactions

A transaction that began earlier may still be active and holding a necessary lock, blocking subsequent requests for the same database object.

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Inappropriate Isolation Level

Using stricter transaction isolation levels (e.g., SERIALIZABLE) can increase the likelihood of lock contention and this error during concurrent operations.

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Solutions

3 solutions available

1. Identify and Terminate Blocking Processes medium

Find the sessions holding the lock and terminate them if necessary.

1

Connect to your PostgreSQL database using psql or your preferred client.

psql -U your_user -d your_database -h your_host

2

Query the `pg_locks` and `pg_stat_activity` system views to identify the session holding the lock and the session waiting for it.

SELECT 
    blocked_locks.pid AS blocked_pid,
    blocked_activity.usename AS blocked_user,
    blocked_activity.query AS blocked_query,
    blocking_locks.pid AS blocking_pid,
    blocking_activity.usename AS blocking_user,
    blocking_activity.query AS blocking_query,
    blocking_locks.granted AS granted
FROM pg_locks blocked_locks
JOIN pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid
JOIN pg_locks blocking_locks ON blocking_locks.locktype = blocked_locks.locktype AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
JOIN pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
WHERE blocking_locks.pid != blocked_locks.pid AND NOT blocked_locks.granted;

3

If the blocking session is not performing critical work or is stuck, you can terminate it using `pg_terminate_backend()`. Replace `blocking_pid` with the actual PID identified in the previous step.

SELECT pg_terminate_backend(blocking_pid);

4

Re-run your original query or operation. It should now acquire the lock.

Your original SQL query or operation.

2. Review and Optimize Application Logic for Locking advanced

Examine application code to ensure efficient and timely lock release.

1

Analyze your application's transaction logic. Look for long-running transactions that might be holding locks unnecessarily.

N/A

2

Ensure that locks are acquired only when necessary and released as soon as possible. Avoid holding locks across multiple, unrelated operations.

N/A

3

Consider using advisory locks (`pg_advisory_lock`, `pg_advisory_unlock`) for application-level locking if database object locks are causing contention. These provide more granular control.

SELECT pg_advisory_lock(12345); -- Acquire lock
-- Perform operations
SELECT pg_advisory_unlock(12345); -- Release lock

4

Implement retry mechanisms with backoff in your application for operations that encounter lock contention. This allows the operation to automatically retry after a short delay.

N/A

3. Adjust Lock Timeout Settings easy

Configure PostgreSQL's lock timeout to prevent indefinite waiting.

1

Connect to your PostgreSQL database.

psql -U your_user -d your_database -h your_host

2

Set the `lock_timeout` parameter. This will cause any query that waits for a lock longer than the specified time to return an error (including 55P03). You can set it globally or per session.

SET lock_timeout TO '5s'; -- Sets timeout to 5 seconds for the current session
-- Or globally in postgresql.conf and reload configuration:

3

To set it globally, edit `postgresql.conf` (location varies by OS and installation). Add or modify the following line:

lock_timeout = '5s' # milliseconds, seconds, or intervals

4

After modifying `postgresql.conf`, reload the PostgreSQL configuration for the changes to take effect.

pg_ctl reload -D /path/to/your/data/directory

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Related Errors

5 related errors

PostgreSQL Error 55P03: Lock Not Available