MySQL throws ER_SLAVE_MULTIPLE_CHANNELS_HOST_PORT (error 3075) when you try to create or start a replication channel that already exists for the same host and port.
ER_SLAVE_MULTIPLE_CHANNELS_HOST_PORT (MySQL error 3075) appears when a replication channel for the same host and port already exists. Drop or rename the existing channel, or use a unique host:port combination to resolve the conflict.
ER_SLAVE_MULTIPLE_CHANNELS_HOST_PORT
Error 3075 is raised when MySQL detects that a replication channel with the same host and port is already configured. MySQL allows multiple replication channels, but each must point to a unique host:port pair. Attempting to reuse an existing pair triggers this error.
The error was introduced in MySQL 5.7.6 when multi-source replication became stable. It prevents ambiguous replication states that could corrupt data or cause lag.
The most frequent cause is attempting to create a new channel with the same MASTER_HOST and MASTER_PORT values as an existing channel using CHANGE MASTER TO or START SLAVE commands.
It also appears when restoring configuration files or automating failover scripts that accidentally duplicate channel definitions.
First, list existing channels to confirm the duplicate.
SHOW SLAVE STATUS FOR CHANNEL '';
Then either drop or rename the conflicting channel, or pick a different port.
STOP SLAVE FOR CHANNEL 'sales_replica';
RESET SLAVE FOR CHANNEL 'sales_replica' ALL;
Alternatively, create the new channel with a unique name and host:port.
CHANGE MASTER TO MASTER_HOST='10.0.0.5', MASTER_PORT=3307 FOR CHANNEL 'analytics_replica';
Automated failover tools - Ensure scripts include RESET SLAVE before redeploying a channel.
Server restore - After cloning a replica, run RESET SLAVE ALL to clear old channel metadata.
Adopt a naming convention for channels that matches the host:port, e.g., host3306_main. This prevents accidental reuse.
Monitor replication metadata tables (performance_schema.replication_connection_configuration) and alert on duplicates.
ER_CANT_START_SLAVE (error 1201) occurs when the replica cannot connect to the master - check credentials.
ER_MASTER_INFO (error 1200) signals issues reading the master.info file - fix file permissions.
Running CHANGE MASTER TO twice with the same host and port without resetting the old channel.
Restoring a replica image that already contains channel metadata matching the target host.
Failover scripts recreate channels but omit RESET SLAVE, leaving duplicates.
Occurs when referencing a non-existent channel; ensure the channel is created first.
Raised when a replication command omits FOR CHANNEL and multiple channels exist.
Triggers when the replica cannot connect; usually a credentials or network issue.
Multi-source replication lets one replica pull data from several masters, useful for sharding and consolidation.
Yes, the port differentiates the connection, so using a different port avoids the error.
RESET SLAVE ALL removes relay logs and metadata. Ensure you have backups or use STOP SLAVE first.
Galaxy highlights duplicate CHANGE MASTER commands in the editor and offers AI suggestions to rename or drop channels, preventing error 3075 before execution.