Error 3030 indicates that a multithreaded replica worker thread stopped after a previous error, leaving its last transaction uncommitted to preserve commit order.
ER_SLAVE_WORKER_STOPPED_PREVIOUS_THD_ERROR occurs when a MySQL replica worker thread halts after an earlier failure, leaving one transaction uncommitted. Fix by identifying the failing worker, resolving its error, then restarting all stopped workers with START REPLICA APPLY_THREAD to restore replication.
ER_SLAVE_WORKER_STOPPED_PREVIOUS_THD_ERROR
Error 3030 appears on a MySQL replica that uses multithreaded replication with slave-preserve-commit-order enabled. A worker thread terminated after hitting a problem, so MySQL paused that thread before it could commit its last transaction. The SQL thread continues processing other workers, but commit order can no longer be preserved until the broken worker is fixed.
The error is printed in the replica error log and in SHOW REPLICA STATUS. It blocks further commits for that worker, increasing replication lag and risking data inconsistency. Prompt resolution keeps replicas current and avoids failover surprises.
The error is triggered when a worker thread exits abnormally during transaction execution. MySQL protects commit order by rolling back the transaction and halting the worker. Other workers may still apply events, but the sequence guarantee is lost until the stopped thread is restarted.
Primary causes include SQL exceptions in applied events, disk space exhaustion, duplicate key conflicts, unsupported DDL on the replica, or a crash of the worker process due to bugs or OOM events.
First, identify the failing worker and its last error. Query performance_schema.replication_applier_status_by_worker or inspect the replica error log for the thread ID and message.
Next, correct the root problem - for example, add missing indexes, clean disk space, or fix conflicting data. Afterward, restart the stopped worker and verify that replication catches up.
If the worker stopped due to a duplicate key error, the conflicting row likely already exists on the replica. Delete or update the row to match the source, then restart the worker.
If the worker failed on a DDL statement, ensure the replica schema matches the source. Apply the missing ALTER statement manually, restart the thread, and monitor.
Maintain identical schemas across source and replica using automated migrations. Validate replication on staging before promoting changes.
Enable monitoring for replica error logs and replication lag. Set alarm thresholds so you can react before commit order is violated.
Error 3020 (ER_SLAVE_THREAD_TIMEOUT) indicates a worker timed out waiting for locks. Tune lock waits and restart the worker.
Error 1594 (ER_SLAVE_SQL_THREAD_BROKEN) stops the entire SQL thread. Investigate the error log and restart replication once fixed.
An UPDATE or INSERT applied by the worker violates constraints, causing a duplicate key or foreign key failure that stops the thread.
Insufficient storage prevents the worker from writing relay logs or tmp files, forcing it to abort.
Differing table definitions make incoming DDL or DML invalid on the replica, terminating the worker.
Out-of-memory killer or segfault ends the worker process, triggering error 3030.
The main SQL thread stopped due to an unrecoverable error. Similar troubleshooting steps apply, but you must restart the SQL thread instead of an individual worker.
A worker exceeded the slave_pending_jobs_size limit or waited too long on a lock. Adjust timeout or resolve locking issue and restart.
Replication is temporarily silenced because too many errors occurred. Clear errors, then issue SET GLOBAL sql_slave_skip_counter = N followed by START REPLICA.
No. Other workers may apply events, but commit order is violated and data divergence is possible. Always resolve and restart the stopped worker.
A full restart initializes threads, but the underlying transaction error persists. Fix the data issue before restarting to avoid repeated failures.
Galaxy highlights replication errors in query results and lets teams share the exact diagnostic SQL quickly, reducing mean time to repair.
Error 3030 was introduced in 5.7.5 but exists in later 8.x versions when multithreaded replicas use preserve commit order.
.avif)
.avif){kind=logo}
