clickhouse commands

17 commands, each with a one-line explanation. Click a command to copy it, or its title for details.

Commands 17 shown

  • Connect to clickhouse-client
    clickhouse-client -h clickhouse -u default --password <pass> --database mydb

    Open interactive ClickHouse CLI session

  • Show databases
    clickhouse-client -q 'SHOW DATABASES'

    List all databases in ClickHouse

  • Show tables
    clickhouse-client -q 'SHOW TABLES FROM mydb'

    List all tables in a database

  • Table size
    clickhouse-client -q "SELECT table, formatReadableSize(sum(bytes)) AS size FROM system.parts WHERE active AND database='mydb' GROUP BY table ORDER BY sum(bytes) DESC"

    Show disk usage per table in a database

    monitoring

  • Running queries
    clickhouse-client -q 'SELECT query_id, user, elapsed, query FROM system.processes ORDER BY elapsed DESC'

    List all currently running queries with elapsed time

    monitoring · debug

  • Kill query
    clickhouse-client -q "KILL QUERY WHERE query_id='<id>'"

    Terminate a long-running or stuck query

    debug

  • Drop caches
    clickhouse-client -q 'SYSTEM DROP MARK CACHE; SYSTEM DROP UNCOMPRESSED CACHE'

    Flush ClickHouse caches to free memory

  • Sync replica
    clickhouse-client -q 'SYSTEM SYNC REPLICA mydb.myTable'

    Force replica to sync with ZooKeeper state

    monitoring

  • Connect and run a query
    clickhouse-client --host ch.example.com --user default --password secret -q 'SELECT version()'

    Execute a one-shot query via clickhouse-client

  • Check running queries
    clickhouse-client -q 'SELECT query_id, elapsed, query FROM system.processes ORDER BY elapsed DESC LIMIT 10'

    List longest running queries in the system

    debug · monitoring

  • Kill a running query
    clickhouse-client -q "KILL QUERY WHERE query_id = 'abc-123'"

    Force-stop a specific query by its query_id

    debug

  • Table disk usage
    clickhouse-client -q 'SELECT database, table, formatReadableSize(sum(bytes_on_disk)) AS size FROM system.parts GROUP BY database, table ORDER BY sum(bytes_on_disk) DESC LIMIT 20'

    Top 20 tables by on-disk size

    monitoring

  • Optimize table (force merge)
    clickhouse-client -q 'OPTIMIZE TABLE mydb.mytable FINAL'

    Force merging of all parts (use with caution on large tables)

  • Ingest CSV from file
    clickhouse-client --query 'INSERT INTO mydb.events FORMAT CSVWithNames' < events.csv

    Bulk-load a CSV file into a ClickHouse table

  • Check replication status
    clickhouse-client -q 'SELECT database, table, is_leader, queue_size, absolute_delay FROM system.replicas WHERE absolute_delay > 0'

    Show replication lag on delayed replicas

    monitoring

  • Slowest recent queries
    clickhouse-client -q "SELECT query_duration_ms, formatReadableSize(memory_usage) mem, substring(query,1,80) FROM system.query_log WHERE type=2 AND event_time>now()-3600 ORDER BY query_duration_ms DESC LIMIT 10"

    Top slow finished queries last hour with memory; type=2 = QueryFinish

    performance · troubleshooting · observability

  • Pending mutations
    clickhouse-client -q "SELECT database, table, mutation_id, latest_fail_reason FROM system.mutations WHERE is_done=0"

    Find stuck ALTER/DELETE mutations with failure reason; blocks schema changes

    troubleshooting · debug · monitoring