The applier module of MySQL Group Replication could not start, so START GROUP_REPLICATION fails with error 3094.
ER_GROUP_REPLICATION_APPLIER_INIT_ERROR occurs when MySQL cannot initialize the Group Replication applier thread. Check replication filters, privileges, and plugin settings, then restart group replication to resolve the issue.
ER_GROUP_REPLICATION_APPLIER_INIT_ERROR
MySQL throws error 3094 with SQLSTATE HY000 when the Group Replication applier thread cannot start. The server aborts the START GROUP_REPLICATION command to protect data consistency.
Because the applier thread replays remote transactions on the local instance, its failure leaves the node unable to synchronize, so the cluster will not include this member.
Misconfigured replication filters, missing privileges, or plugin version mismatches can block the applier from initializing.
Disk-full situations, read-only mode, or crashed relay logs may also stop the applier thread before it begins.
Review the MySQL error log first; it lists the exact sub-error that prevented initialization. Correct the specific issue, then restart Group Replication.
Typical fixes include granting missing permissions, clearing relay logs, or aligning group_replication_filters across all members.
If a node was cloned, its server_uuid may collide. Regenerate a unique UUID, restart the server, and re-join the group.
When GTID purged entries differ, set GTID_PURGED on the joining server to match the primary, then start replication again.
Keep all nodes on the same major and minor MySQL version to avoid plugin incompatibility problems.
Automate validation of group_replication_* parameters during deployment using tools like Galaxy so configuration drifts are caught early.
ER_GROUP_REPLICATION_COMMUNICATION_ERROR (3092) signals network layer issues, while ER_GROUP_REPLICATION_SQL_THREAD_ERROR (3093) points to SQL thread failures. Their troubleshooting steps overlap with applier errors.
Differing group_replication_recovery_channel or replication_do_db settings block the applier.
The replication user lacks APPLY_REPLICATION_APPLIER or related grants.
Joining node runs a different group_replication plugin build than primary nodes.
Relay log files or GTID execution tables are inconsistent or unreadable.
Log write failures arise when the filesystem hosting relay logs is full.
Indicates network or plugin communication failure between group members.
Signals the SQL thread failed to apply transactions after initialization.
Occurs when an already running applier thread stops unexpectedly.
No. The local instance stays online in standalone mode, but it is removed from the replication group.
Forcing join is unsafe. Resolve the root cause, then issue START GROUP_REPLICATION again.
Galaxy surfaces configuration drift via AI-assisted linting, alerting you when replication parameters differ across servers.
Upgrade only after confirming plugin compatibility across all nodes and scheduling downtime.
.avif)
.avif){kind=logo}
