How Do I Quickly Restore ClickHouse When Concurrent Requests Are Stacked for a Long Time?
Symptom
When there are too many concurrent ClickHouse requests, new requests cannot be handled, affecting service availability. The error information is as follows:
DB::Exception: Too many simultaneous queries. Maximum: 100
Procedure
- Log in to the ClickHouse client node and connect to the server where the error is reported. For details, see ClickHouse Client Practices.
- Run the following command to check the number of concurrent SQL jobs that are being executed:
select count(*) from system.processes;
Verify that the obtained value is greater than or equal to 100.
- Run the following command to stop large query SQL statements that are being executed:
kill query where query_kind='Select' and elapsed > 60;
- Wait for 30 seconds and run the following command to collect statistics on the SQL jobs that are being executed:
select count(*) from system.processes;
Check whether the obtained value is less than 60.
- If the number of concurrent jobs is greater than 60, log in to FusionInsight Manager, choose Cluster > Services > ClickHouse > Instances, select the ClickHouseServer instance that reports the error, and choose More > Restart Instance.
Feedback
Was this page helpful?
Provide feedbackThank you very much for your feedback. We will continue working to improve the documentation.