Error
Error Code:
40000
PostgreSQL Error 40000: Forced Transaction Rollback
Description
The 'transaction rollback' error (40000) indicates that a database transaction has been aborted, and all uncommitted changes made within it have been undone. This typically occurs when the database system encounters a critical condition preventing the transaction from completing successfully, or when an explicit rollback command is issued.
Error Message
transaction rollback
Known Causes
4 known causesDatabase Deadlock
Two or more transactions are waiting for each other to release locks, leading the database to abort one transaction to resolve the contention.
Query Timeout
A specific query or the entire transaction exceeded its configured execution time limit (e.g., `statement_timeout`), causing the database to cancel and roll back the operation.
Client Disconnection
The client application or session initiating the transaction disconnected unexpectedly, prompting the database to automatically roll back any pending changes.
Explicit Rollback Command
The transaction was intentionally aborted by an explicit `ROLLBACK` SQL command issued by the application or a user.
Solutions
3 solutions available1. Identify and Resolve Concurrent Transaction Conflicts advanced
Analyze logs to pinpoint conflicting transactions and adjust application logic or timeouts.
1
Examine PostgreSQL logs for the exact timestamp and context of the `transaction rollback` error. Look for messages indicating lock contention or deadlocks. The `log_statement` parameter in `postgresql.conf` can be set to 'all' or 'ddl' temporarily to capture more information, but be mindful of performance impact.
2
Use `pg_locks` and `pg_stat_activity` views to identify the transactions involved in the conflict. Pay attention to `wait_event_type` and `wait_event` columns in `pg_stat_activity`.
SELECT pid, datname, usename, query, wait_event_type, wait_event FROM pg_stat_activity WHERE state = 'active' AND wait_event IS NOT NULL;3
If a deadlock is detected, PostgreSQL automatically rolls back one of the transactions. Understand the application logic that leads to these deadlocks. This might involve reordering operations, using advisory locks, or implementing retry mechanisms in your application.
4
Consider adjusting `statement_timeout` and `lock_timeout` parameters in `postgresql.conf` or per-session to prevent long-running transactions from holding locks indefinitely, which can contribute to deadlocks.
ALTER SYSTEM SET statement_timeout = '5s';
ALTER SYSTEM SET lock_timeout = '2s';
SELECT pg_reload_conf();2. Address Constraint Violations medium
Ensure data integrity by fixing invalid data that violates unique, foreign key, or check constraints.
1
When a `transaction rollback` occurs due to a constraint violation (e.g., `unique_violation`, `foreign_key_violation`, `check_violation`), the error message will typically indicate the specific constraint that was violated. Review your application's data insertion or update logic.
2
Identify the data that is causing the constraint violation. You might need to query the table involved to find the offending rows. For example, if a unique constraint on `email` is violated, search for duplicate email addresses.
SELECT email, COUNT(*) FROM users GROUP BY email HAVING COUNT(*) > 1;3
Correct the invalid data. This might involve updating existing records, deleting duplicate or invalid entries, or adjusting the data being inserted/updated by your application. If it's a foreign key violation, ensure the referenced record exists.
4
If the constraint is too restrictive for your application's needs, consider altering the constraint or disabling it temporarily (with caution) while you address the data or application logic. However, this should be a last resort.
ALTER TABLE your_table DISABLE TRIGGER ALL;
-- Perform data cleanup
ALTER TABLE your_table ENABLE TRIGGER ALL;3. Manage Resource Exhaustion medium
Increase available resources like memory or disk space, or optimize queries to reduce resource consumption.
1
Monitor PostgreSQL server resources such as CPU, memory, and disk I/O. High resource utilization can lead to transactions being forcibly rolled back to maintain system stability.
2
Check PostgreSQL's `pg_settings` for parameters like `shared_buffers`, `work_mem`, and `maintenance_work_mem`. If these are too low for your workload, consider increasing them. Be careful not to over-allocate, as this can lead to swapping.
SHOW shared_buffers;
SHOW work_mem;
ALTER SYSTEM SET shared_buffers = '256MB';
ALTER SYSTEM SET work_mem = '16MB';
SELECT pg_reload_conf();3
Ensure there is sufficient free disk space on the server where PostgreSQL data files are stored. Running out of disk space will cause write operations to fail, leading to rollbacks.
df -h4
Optimize slow or resource-intensive queries. Use `EXPLAIN ANALYZE` to identify queries that are consuming excessive resources and refactor them, add appropriate indexes, or rewrite them to be more efficient.
EXPLAIN ANALYZE SELECT * FROM large_table WHERE some_column = 'value';