MySQL raises ER_SLAVE_CHANNEL_MUST_STOP when a replication modification is attempted on a channel that still has running threads.
ER_SLAVE_CHANNEL_MUST_STOP (MySQL error 3081) appears when you run replication commands while a channel is active. Stop the channel with STOP SLAVE FOR CHANNEL 'name', apply your change, then START SLAVE to clear the error.
ER_SLAVE_CHANNEL_MUST_STOP
MySQL raises ER_SLAVE_CHANNEL_MUST_STOP (error 3081, SQLSTATE HY000) when you attempt to run a replication statement on a channel that still has active I/O or SQL threads. The server blocks the action to keep replication data consistent.
The error appears during operations like CHANGE MASTER TO, RESET SLAVE, or STOP GROUP_REPLICATION if you neglect to pause the channel. Since MySQL 5.7.6, multiple channels are supported, so the message contains the channel name.
The error triggers whenever you change source details, skip transactions, or clone data while replication threads are running. It can surface in classic asynchronous replication, semi-synchronous setups, and Group Replication channels.
Automation tools that perform maintenance without a pre-stop step will also surface the error, often halting CI pipelines until corrected.
Proceeding without stopping the channel risks metadata corruption, GTID inconsistency, or replication lag. Clearing the error quickly maintains replica integrity and avoids extended downtime.
Active I/O or SQL threads prevent configuration changes, leading to the error. Forgetting to stop a secondary channel during migrations is a frequent cause.
Scripts that run CHANGE MASTER TO or RESET SLAVE directly, without issuing STOP SLAVE FOR CHANNEL, also trigger the message.
First, confirm thread status with SHOW SLAVE STATUS FOR CHANNEL. Next, stop the channel using STOP SLAVE FOR CHANNEL 'name'. Perform the desired operation, then restart the channel with START SLAVE.
If you have multiple channels, repeat the procedure for each affected channel to avoid partial updates.
During host migration, administrators often forget to stop the replica before pointing to a new source. The fix is to pause the channel, change the master, and restart.
In CI pipelines, adding a STOP SLAVE FOR CHANNEL step before configuration commands eliminates build failures.
Create a replication maintenance checklist that always includes STOP SLAVE FOR CHANNEL before any metadata change and START SLAVE after.
Use monitoring tools or Galaxy's AI copilot to flag scripts that bypass the stop-step, reducing human error in busy environments.
ER_SLAVE_MUST_STOP (1199) affects the default channel and is fixed the same way: stop the replica first. ER_SQL_THREAD_MUST_STOP (1768) requires pausing the SQL thread before GTID_SKIP operations.
The I/O or SQL thread is still running on the specified channel, blocking any configuration changes.
Deployment or backup scripts issue CHANGE MASTER TO or RESET SLAVE without first executing STOP SLAVE FOR CHANNEL.
Administrators stop the default channel but forget to stop a secondary channel introduced for parallel replication or migration.
Error 1199 appears when you try to reset the default replica without stopping it first.
Error 1768 is raised when you attempt a GTID_SKIP command while the SQL thread is active.
Error 1677 shows up if table definitions differ between source and replica when replication resumes.
Yes. MySQL requires the channel to be inactive to guarantee a consistent change of replication metadata.
The error text includes the channel name. Use SHOW SLAVE STATUS FOR CHANNEL 'name' to inspect it.
Writes on the primary continue. Only the replica falls behind while stopped. Restart replication to catch up.
Galaxy's AI copilot warns when your script issues replication commands without a preceding STOP SLAVE, reducing human error.
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