<p>Error 1608 appears when START SLAVE or CHANGE MASTER TO is issued with conflicting or overlapping replication mode options, leaving MySQL unable to determine the correct slave state.</p>
<p>MySQL Error 1608: ER_NEVER_USED arises when replication commands combine incompatible or duplicate slave mode flags, creating an ambiguous configuration. Remove the conflicting clauses (for example, drop MASTER_AUTO_POSITION when also setting MASTER_LOG_FILE) and restart replication to resolve the issue.</p>
Ambiguous slave modes combination. %s
Error 1608 occurs during replication setup when MySQL encounters an ambiguous slave modes combination. The server receives overlapping or mutually exclusive options in START SLAVE, CHANGE MASTER TO, or related replication statements and cannot decide which mode to apply.
This error is flagged with SQLSTATE HY000, indicating a general execution failure. Although named ER_NEVER_USED, it is actively thrown in replication code paths where conflicting flags are detected.
The error typically appears immediately after executing a replication command that mixes new and legacy parameters. Mixing MASTER_AUTO_POSITION with file/position coordinates, or combining multithreaded slave flags with single-threaded options, are frequent triggers.
It may also arise during automated deployment scripts that dynamically assemble replication statements without validating option compatibility.
Replication will not start until the conflict is resolved, leaving replicas stale and increasing recovery point objective. In production, delayed replicas compromise failover strategies and read-scaling workloads.
Quick correction ensures data consistency, high availability, and uninterrupted scaling, especially in environments that rely on Galaxy or other tooling for query offloading.
Using MASTER_AUTO_POSITION = 1 together with MASTER_LOG_FILE or MASTER_LOG_POS confuses MySQL, because auto-position replaces file/position replication.
Specifying SQL_THREAD and IO_THREAD flags alongside UNTIL conditions that apply to both threads can lead to ambiguity.
Combining deprecated START SLAVE clauses such as UNTIL SQL_AFTER_MTS_GAPS with modern MTS-safe options in the same statement triggers the error.
Configuration management tools sometimes concatenate option strings twice, producing duplicate keywords that MySQL interprets as conflicting modes.
Indicates issues starting slave threads; may follow 1608 if ambiguity remains.
Raised when a replica cannot read the master’s binlog, often after an incorrect change master.
Signals communication failure during master connection phase.
Occurs when GTID_PURGED is modified while replication is active, similar configuration context.
No. It only means the server cannot decide which slave mode to use. Correct the conflicting options and replication will start normally.
MySQL will not proceed automatically. You must edit the replication command to remove ambiguity.
The code exists in MySQL 5.6 and later. Newer versions refine detection but the root cause remains conflicting options.
Galaxy stores audited, endorsed replication scripts so teams reuse the same, tested commands, drastically reducing configuration mistakes that trigger Error 1608.
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