Remote connection refused

Check: listen_host config; firewall. Fix: Both closed by default — open deliberately with authenticated users.

Memory limit exceeded on query

Check: max_memory_usage setting. Fix: Raise per-user limit in users.d or add RAM; ClickHouse is honest about memory.

Check: Storage type. Fix: Use gp3/io2 with adequate IOPS; ClickHouse is IO-hungry on cold reads.

Troubleshoot ClickHouse (Hardened) — DC Associates Group Docs

Symptom	Check	Fix
Remote connection refused	listen_host config; firewall	Both closed by default — open deliberately with authenticated users.
Memory limit exceeded on query	max_memory_usage setting	Raise per-user limit in users.d or add RAM; ClickHouse is honest about memory.
Slow cold queries	Storage type	Use gp3/io2 with adequate IOPS; ClickHouse is IO-hungry on cold reads.

Logs & useful commands

/var/log/clickhouse-server/; `journalctl -u clickhouse-server -f`
Health: clickhouse-client -q 'SELECT 1'
First boot state: Service enabled at build; ready in seconds.

Still stuck? Email support@dcassociatesgroup.com with the product name, cloud + region, instance size, and the output of the health command — first response within 1 business day, most tickets same-day.