Is ClickHouse down today?

How to Contact ClickHouse Technical Support?

- Official Website at https://clickhouse.com;

- Community Slack at https://clickhouse.com/slack;

- GitHub Issues at https://github.com/ClickHouse/ClickHouse/issues;

- Documentation at https://clickhouse.com/docs;

- Community Forum at https://github.com/ClickHouse/ClickHouse/discussions;

- Cloud Support at https://clickhouse.cloud/support (for cloud customers).

Latest News and Current Information:

- Official Website - https://clickhouse.com;

- Documentation - https://clickhouse.com/docs;

- GitHub - https://github.com/ClickHouse/ClickHouse;

- Blog - https://clickhouse.com/blog;

- X (Twitter) - https://twitter.com/ClickHouseDB;

- YouTube - https://www.youtube.com/c/ClickHouseDB;

- LinkedIn - https://www.linkedin.com/company/clickhouse;

- Slack Community - https://clickhouse.com/slack;

- Cloud Status - https://status.clickhouse.cloud;

- Release Notes - https://clickhouse.com/docs/en/whats-new/changelog.

ClickHouse Database Outage: OLAP System Service Down

Service disruptions manifest as ClickHouse server not responding, queries timing out, connection refused errors, cluster unreachable, or complete database unavailable.

- Check ClickHouse server status: `systemctl status clickhouse-server`;

- Review server logs: `/​var/​log/​clickhouse-​server/​clickhouse-​server.​log`;

- Verify server process running: `ps aux | grep clickhouse`;

- Check port 8123 (HTTP) or 9000 (native) accessible;

- Restart server: `sudo systemctl restart clickhouse-server`;

- Verify configuration file syntax correct;

- Check disk space available;

- Review resource usage (CPU/RAM);

- Test local connection: `clickhouse-client`;

- Monitor ClickHouse Cloud status if using managed service.

Query Performance Problem: ClickHouse Queries Running Slow

Performance issues include slow SELECT queries, high memory usage, timeouts, INSERT delays, or merge operations blocking.

- Check query execution plan with EXPLAIN;

- Review running queries: `SHOW PROCESSLIST`;

- Kill long-running queries if needed;

- Verify table partitioning configured;

- Check primary key and indexes optimal;

- Review merge tree settings;

- Monitor system.query_log table;

- Optimize table manually if needed;

- Check background merge activity;

- Review max_threads and max_memory settings.

Connection or Authentication Fault: Cannot Connect to ClickHouse

Connection problems include authentication failing, "Connection refused", network unreachable, SSL errors, or user permission denied.

- Verify credentials correct;

- Check user permissions granted;

- Review users.xml configuration;

- Test connection with clickhouse-client;

- Verify firewall allows connections;

- Check listen_host configuration;

- Review network security settings;

- Test with different client/driver;

- Verify SSL certificates if enabled;

- Check access control policies.

Data Insertion Issue: Cannot INSERT Data into ClickHouse

INSERT problems include "Table doesn't exist" errors, data type mismatches, quota exceeded, read-only mode, or replication lag.

- Verify table exists in database;

- Check column data types match;

- Review INSERT query syntax;

- Check user write permissions;

- Verify quota not exceeded;

- Check table not in readonly mode;

- Review replication queue status;

- Verify partition key values valid;

- Check disk space sufficient;

- Review server error logs.

ClickHouse Cluster Problem: Distributed Queries Failing

Cluster issues include replica unavailable, ZooKeeper connection lost, distributed table errors, shard unreachable, or replication broken.

- Check all cluster nodes online;

- Verify ZooKeeper service running;

- Review cluster configuration correct;

- Test connection to each shard;

- Check replica status in system.replicas;

- Verify network between nodes stable;

- Review distributed_ddl_queue table;

- Check replication queue not stuck;

- Verify ZooKeeper quorum healthy;

- Review remote_servers configuration.

Memory or Resource Issue: ClickHouse Out of Memory

Resource problems include OOM errors, server crashes, "Memory limit exceeded", high CPU usage, or swap thrashing.

- Check memory usage: `clickhouse-client -q "SELECT * FROM system.metrics"`;

- Review max_memory_usage settings;

- Kill memory-heavy queries;

- Optimize queries to use less memory;

- Increase server RAM if needed;

- Check background merges resource usage;

- Review max_bytes_before_external_* settings;

- Monitor system.asynchronous_metrics;

- Adjust max_server_memory_usage;

- Check for memory leaks in logs.

Table or Partition Problem: ClickHouse Table Issues

Table management issues include table corruption, partition not dropping, ALTER failing, metadata errors, or detached parts.

- Check table structure: `DESCRIBE table`;

- Verify table engine configuration;

- Review detached parts directory;

- Attempt table repair if needed;

- Check partition expressions valid;

- Review ALTER TABLE operation logs;

- Verify no locks blocking operations;

- Check mutations status;

- Review system.parts table;

- Backup before major changes.

Backup or Restore Fault: ClickHouse Backup Failing

Backup problems include snapshot creation errors, restore failing, data corruption, insufficient space, or clickhouse-backup issues.

- Use clickhouse-backup tool properly;

- Check backup storage sufficient;

- Verify backup configuration correct;

- Test restore on separate instance;

- Review backup logs for errors;

- Check S3/filesystem permissions;

- Verify incremental backup chain;

- Use FREEZE TABLE for snapshots;

- Check backup retention policy;

- Test disaster recovery procedure.

Materialized View Issue: MV Not Updating

Materialized view problems include MV not populating, data lag, refresh errors, target table issues, or query failures.

- Check MV definition correct;

- Verify source table receiving data;

- Review MV target table exists;

- Check for errors in system.query_log;

- Drop and recreate MV if needed;

- Verify POPULATE used if required;

- Check resource limits not blocking;

- Review MV query performance;

- Monitor MV refresh frequency;

- Check dependencies resolved.

ClickHouse Cloud Service Problem: Managed Service Issues

Cloud-specific issues include service unavailable, scaling problems, API errors, billing issues, or connectivity to cloud instance.

- Check ClickHouse Cloud status page;

- Verify cloud credentials valid;

- Review service tier limits;

- Check API quota not exceeded;

- Test connection string correct;

- Verify IP whitelist configured;

- Review cloud console for alerts;

- Check billing account active;

- Monitor auto-scaling behavior;

- Contact cloud support team.

Integration or Driver Fault: Client Libraries Not Working

Integration problems include JDBC/ODBC errors, Python driver issues, API failures, incompatible versions, or connection pooling problems.

- Update driver to latest version;

- Verify driver compatibility with server;

- Check connection parameters correct;

- Review driver documentation;

- Test with official clients first;

- Check SSL/TLS settings match;

- Verify connection pool configuration;

- Review driver error messages;

- Test with simple queries first;

- Check for known driver bugs.

Configuration or Settings Issue: ClickHouse Misconfigured

Configuration problems include invalid settings, server won't start, config merge errors, profile issues, or setting overrides failing.

- Verify XML syntax in config files;

- Check config.xml and users.xml valid;

- Review configuration merge priority;

- Test config with --config-file option;

- Check included config files exist;

- Verify settings not conflicting;

- Review system.settings table;

- Check server startup logs;

- Validate changes before restart;

- Keep backup of working configs.