MySQL throws error 3080 when a replica tries to create or start a replication channel beyond the server's maximum channel limit.
ER_SLAVE_MAX_CHANNELS_EXCEEDED appears when MySQL has already reached its channel limit, blocking new replication channels. Drop or reuse an existing channel, or restart with a higher limit (5.7 only) to resolve the error.
ER_SLAVE_MAX_CHANNELS_EXCEEDED
MySQL raises the error ER_SLAVE_MAX_CHANNELS_EXCEEDED: Maximum number of replication channels allowed exceeded when you attempt to create or start a replica channel after the configured limit is hit.
The limit depends on slave_parallel_workers in MySQL 5.7 or the fixed ceiling of 512 in MySQL 8. When the server cannot register another channel, statements such as CHANGE REPLICATION SOURCE TO or START REPLICA CHANNEL fail with SQL state HY000 and error code 3080.
Resolving the issue is critical because the extra channel will not start, halting data flow to downstream replicas, read pools, or disaster recovery sites.
The server counts every named replication channel, including those in STOPPED or ERROR state. Test scripts, sharding frameworks, or CI pipelines that create channels dynamically can exhaust the limit quickly.
A channel left behind after a failed deployment also occupies a slot, so the limit is reached even though the channel is unused.
The fastest remedy is to stop and drop channels that are no longer required. If you still need more channels and run MySQL 5.7, restart mysqld with a higher slave_parallel_workers value, but never above 512.
Multi source replication, per tenant sharding, and automated database tests frequently trigger the error. Cleaning up after each run or reusing a generic channel solves most cases.
Monitor the current channel count, reuse existing channels when possible, and include RESET REPLICA ALL FOR CHANNEL steps in tear-down scripts.
ER_SLAVE_CHANNEL_DOES_NOT_EXIST is raised when a referenced channel is missing, and ER_SLAVE_MULTIPLE_CHANNELS_HOSTPORT occurs when duplicate source host and port combinations are configured. Both issues are fixed by proper channel management.
CI pipelines that create temporary channels without dropping them steadily consume the global limit.
Allocating one channel per tenant or shard can exceed 512 as the business grows.
Scripts that generate a fresh UUID based channel name on every run leak channels until the limit is reached.
Raised when a statement references a channel that is not present in mysql.slave_master_info.
Occurs when two channels point to the same source host and port combination.
Triggered when the channel name exceeds 64 characters or contains invalid symbols.
MySQL 5.7 and 8 allow up to 512 channels per replica.
No. The limit is fixed. Only a restart with a different slave_parallel_workers value can raise it in 5.7.
Yes. After RESET REPLICA ALL FOR CHANNEL the slot is released and a new channel can be created.
Galaxy keeps replication scripts version controlled and visible, reducing orphan channels and alerting teams when counts approach the limit.
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