Cluster Configuration FAQ
ClickHouse does not start, some other unexpected behavior happening
Check clickhouse logs, they are your friends:
tail -n 1000 /var/log/clickhouse-server/clickhouse-server.err.log | less tail -n 10000 /var/log/clickhouse-server/clickhouse-server.log | less
How Do I Restrict Memory Usage?
See our knowledge base article and official documentation for more information.
ClickHouse died during big query execution
Misconfigured clickhouse can try to allocate more RAM than is available on the system.
In that case an OS component called oomkiller can kill the clickhouse process.
That event leaves traces inside system logs (can be checked by running dmesg command).
How Do I make huge ‘Group By’ queries use less RAM?
Enable on disk GROUP BY (it is slower, so is disabled by default)
Set max_bytes_before_external_group_by to a value about 70-80% of your max_memory_usage value.
Data returned in chunks by clickhouse-client
I Can’t Connect From Other Hosts. What do I do?