MySQL raises ER_NO_SUCH_THREAD when a session references or tries to kill a connection ID that no longer exists on the server.
MySQL Error 1094 ER_NO_SUCH_THREAD means the thread ID you referenced is gone, usually because the connection already closed. Run SHOW PROCESSLIST to get a fresh ID, then rerun your KILL or diagnostic command with the correct value to resolve the problem.
Unknown thread id: %lu
Error 1094 appears with the message “Unknown thread id: N” when MySQL cannot find the thread you specified in a KILL, SHOW PROFILE, or PERFORMANCE_SCHEMA query.
The server removed the thread because the client disconnected or the query finished. Any later attempt to address that thread fails with ER_NO_SUCH_THREAD, blocking monitoring or termination tasks until you use a valid ID.
Referencing an outdated thread ID is the primary trigger.
After a connection ends, its ID becomes invalid immediately, even if another session soon reuses the same numeric value.
Race conditions in scripts that fetch the process list and then issue KILL can surface the problem. In busy servers, a thread may disappear between the two commands.
First confirm the target thread still exists. Run SHOW PROCESSLIST or query PERFORMANCE_SCHEMA to obtain a current list of connection IDs.
Use the freshest ID in your subsequent command.
If you automate thread management, wrap KILL calls in error handling that retries after refreshing the process list. This pattern eliminates hard failures during transient disconnects.
When debugging a runaway query, DBAs often copy an ID from an old log. Always cross-check the ID before issuing KILL to avoid Error 1094.
Monitoring tools that cache thread IDs across polling cycles can raise false alarms.
Configure them to pull the ID and act within the same transaction to keep data current.
Automate thread actions in single scripts that retrieve and kill in one step. Add IF(@@error) handling so your workflow continues even if a thread vanishes.
Galaxy’s live query lists and AI snippets surface only active connection IDs, preventing stale references and making KILL commands safer.
Error 1095 (ER_KILL_DENIED) occurs when you try to kill a privileged thread.
Check privileges and use SUPER or SYSTEM_USER role.
Error 2013 (Lost connection to MySQL server) differs because it indicates the client, not the thread, dropped unexpectedly. Reconnect before retrying commands.
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Admins copy a thread ID from a slow query log, but by the time they run KILL, the query has finished and the ID is invalid.
A script calls SHOW PROCESSLIST, waits a few seconds, then sends KILL.
The delay lets the thread end naturally, producing ER_NO_SUCH_THREAD.
Developers sometimes confuse CONNECTION_ID() (their own session) with the target ID and attempt to kill a nonexistent thread number.
High-throughput pools open and close sessions rapidly, causing IDs to disappear between monitoring cycles.
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The thread likely finished between your SHOW PROCESSLIST and KILL commands. MySQL released the ID, so it no longer exists.
Not simultaneously. MySQL reuses numbers over time, but a given ID belongs to only one live thread at a time.
No. The error is informational. It indicates your command had no effect because the target thread was gone.
Galaxy’s real-time process list and AI suggestions always surface live IDs, reducing the chance you issue KILL against a stale thread.
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