Drop caches

Flush ClickHouse caches to free memory

clickhouse-client -q 'SYSTEM DROP MARK CACHE; SYSTEM DROP UNCOMPRESSED CACHE'
tool
clickhouse17 commands
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clickhouse

More clickhouse commands

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

    Force replica to sync with ZooKeeper state

  • 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

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

    Force-stop a specific query by its query_id

  • 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

all 17 clickhouse commands