<p>Feature not supported while replication runs in multi-threaded slave mode.</p>
<p>MySQL Error 1753 ER_MTS_FEATURE_IS_NOT_SUPPORTED arises when you execute a statement that the replica cannot handle in multi-threaded slave (MTS) mode. Disable the conflicting feature or switch the replica to single-threaded mode to resolve the issue.</p>
%s is not supported in multi-threaded slave mode. %s
MySQL raises error 1753 with the message "%s is not supported in multi-threaded slave mode" when a feature incompatible with multi-threaded replication is executed on a replica running in MTS mode.
The server halts the SQL thread to protect data consistency because the requested operation cannot be parallelized safely.
The error appears during replication on the replica side, not on the primary, and only when slave_parallel_workers is greater than zero, indicating multi-threaded execution.
Typical triggers include online DDL, temporary tables, or unsafe system variables that require single-thread guarantees.
Leaving the replica stopped breaks high availability and backup pipelines. Lag grows, compromising data freshness for analytics and failover readiness.
Prompt resolution restores replication flow and ensures your read replicas and disaster-recovery nodes remain current.
Certain ALTER TABLE operations cannot be parallelized and immediately trigger the error.
Statements that create or manipulate nontransactional temporary tables are blocked in MTS mode.
Functions like UUID() inside transactional updates can be unsafe for parallel replication.
Settings such as binlog_format=MIXED combined with statement-based logging confuse the applier threads.
Occurs when the replica cannot read the relay log, often due to disk issues.
Signals a write error on the relay log file system.
Happens when a write is attempted on a read-only replica.
Yes. Set slave_parallel_workers to 0 in my.cnf and restart MySQL. Replication will always run single-threaded.
All versions supporting MTS, including 5.6, 5.7, 8.0, can raise error 1753 when an unsafe feature is used.
No. It only stops the SQL thread on the replica. The primary continues to operate normally.
Galaxy's AI copilot flags unsafe DDL and provides replication-safe alternatives before you run queries, reducing the chance of replication stops.
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