Check replication status

Show replication lag on delayed replicas

clickhouse-client -q 'SELECT database, table, is_leader, queue_size, absolute_delay FROM system.replicas WHERE absolute_delay > 0'
tool
clickhouse17 commands
tags
clickhousemonitoring

More clickhouse commands

  • 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

  • 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

  • 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

all 17 clickhouse commands