The observer process failed while executing a replication hook, triggering error 3100.
MySQL Error 3100 ER_RUN_HOOK_ERROR appears when the observer thread crashes while running a replication hook. Disable or replace the faulty hook plugin, confirm user privileges, then restart replication to clear the error.
ER_RUN_HOOK_ERROR
MySQL raises error 3100 when the observer thread encounters an unexpected problem while executing a replication hook. Hooks are user defined callbacks that extend replication, so any crash inside them halts the observer and surfaces this runtime error.
The error appears in versions 5.7.6 and later, and it stops the affected channel until the hook issue is resolved. Fixing it quickly keeps replicas in sync and avoids data drift.
Most cases involve bugs or unhandled exceptions in a hook plugin. Missing privileges, wrong parameter types, and version mismatches between master and replica can also crash the observer.
Replication lag amplifies the issue. If the hook reads rows that no longer exist or expects a different schema, the observer fails and MySQL logs ER_RUN_HOOK_ERROR.
First, disable the offending hook so replication can resume. Then audit the hook code, privileges, and parameters. Recompile or upgrade the plugin to match the server version, grant needed privileges, and retest in staging before re-enabling.
If hooks are optional, drop them entirely and restart the replica. Continuous monitoring in Galaxy highlights failing hooks instantly, letting engineers roll back before production lag builds.
Developer pushes a new hook without testing - roll back to the previous binary and restart both observer and IO threads.
Privilege error inside hook - grant the REPLICATION SLAVE or SELECT rights required by the callback, then START SLAVE.
Schema drift between primary and replica - apply the same DDL on replica or adjust hook logic to handle NULLs and defaults safely.
Validate hook code in a staging replica with identical data. Use versioned builds and automated CI checks to compile hooks against the target MySQL release.
Enable detailed error logging and set performance_schema consumers for replication hooks. Galaxy’s query history and commenting keep hook SQL visible, so teams catch breaking changes early.
Error 1594 Relay log read failure - often follows hook crashes that corrupt relay logs; run RESET SLAVE to recover.
Error 1872 Plugin failed to initialize - indicates the hook library could not load, typically due to path or permission issues.
Compiled against a different MySQL version, the binary crashes on function calls.
The hook tries to read or write tables without the proper grants, triggering an exception.
A delayed replica processes outdated rows, causing hook logic to access missing data.
The hook receives unexpected NULL or datatype values and fails to handle them.
Primary and replica run different schemas so column offsets differ during hook execution.
Occurs when the relay log becomes corrupted or unreadable, often after a hook crash.
Raised when MySQL cannot load a hook or plugin library due to path or permission issues.
Appears during replication if DDL statements conflict with existing objects on the replica.
No. Replication stops processing events until the hook issue is fixed, risking data inconsistency.
Dropping a hook stops future callbacks but leaves existing data unchanged, so historical rows remain intact.
A restart clears the in-memory error state, but the faulty hook will trigger the error again unless corrected.
Galaxy surfaces replication errors in real time, lets teams review hook queries collaboratively, and stores version history for safe rollbacks.
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