altinity/altinity-expert-clickhouse-overview

Predefined SQL

Run reporting SQL queries from these files in this skill's directory:

• checks.sql
• metrics.sql
• ddl_queue.sql

Inline SQL below (version/enablement sensitive):

Detached Parts

version-dependent: ClickHouse 23.8 does not have modification_time

SELECT
  hostName() AS host,
  database,
  table,
  reason,
  count() AS detached_parts,
  formatReadableSize(sum(bytes_on_disk)) AS bytes,
  min(modification_time) AS first_detach,
  max(modification_time) AS last_detach
FROM system.detached_parts
GROUP BY host, database, table, reason
ORDER BY detached_parts DESC
LIMIT 100

Text Log

(may be disabled)

select event_date, level, thread_name, any(logger_name) as logger_name,
       message_format_string, count(*) as count
from   system.text_log
where  event_date > now() - interval 24 hour
  and level <= 'Warning'
group by all
order by level, thread_name, message_format_string

Check Pools

WITH
    ['MergesAndMutations', 'Fetches', 'Move', 'Common', 'Schedule', 'BufferFlushSchedule', 'MessageBrokerSchedule', 'DistributedSchedule'] AS pool_tokens,
    ['pool', 'fetches_pool', 'move_pool', 'common_pool', 'schedule_pool', 'buffer_flush_schedule_pool', 'message_broker_schedule_pool', 'distributed_schedule_pool'] AS setting_tokens
SELECT
    extract(m.metric, '^Background(.*)Task') AS pool_name,
    m.active_tasks,
    pool_size,
    round(100.0 * m.active_tasks / pool_size, 1) AS utilization_pct,
    multiIf(utilization_pct > 99, 'Major', utilization_pct > 90, 'Moderate', 'OK') AS severity
FROM
(
    SELECT
        metric,
        value AS active_tasks,
        transform(extract(metric, '^Background(.*)PoolTask'), pool_tokens, setting_tokens, '') AS pool_key,
        concat('background_', lower(pool_key), '_size') AS setting_name
    FROM system.metrics
    WHERE metric LIKE 'Background%PoolTask'
) AS m
LEFT JOIN
(
    SELECT
        name,
        toFloat64OrZero(value) AS pool_size
    FROM system.server_settings
    WHERE name LIKE 'background%pool_size'
) AS s ON s.name = m.setting_name
WHERE pool_size > 0
ORDER BY utilization_pct DESC

On error and for clickhouse version <= 22.8 replace system.server_settings to system.settings

Report

Prepare a summary report based on the findings

Routing Rules (Chain to Other Skills)

Based on findings, load specific modules:

• Replication lag/readonly replicas/Keeper issues → altinity-expert-clickhouse-replication
• High memory usage or OOMs → altinity-expert-clickhouse-memory
• Disk usage > 80% or poor compression → altinity-expert-clickhouse-storage
• Many parts, merge backlog, or TOO_MANY_PARTS → altinity-expert-clickhouse-merges
• Slow SELECTs / heavy reads in query_log → altinity-expert-clickhouse-reporting
• Slow INSERTs / high part creation rate → altinity-expert-clickhouse-ingestion
• Low cache hit ratios / cache pressure → altinity-expert-clickhouse-caches
• Dictionary load failures or high dictionary memory → altinity-expert-clickhouse-dictionaries
• Frequent exceptions or error spikes → include system.errors and system.*_log summaries below
• System log TTL issues or log growth → altinity-expert-clickhouse-logs
• Schema anti‑patterns (partitioning/ORDER BY/MV issues) → altinity-expert-clickhouse-schema
• High load/connection saturation/queue buildup → altinity-expert-clickhouse-metrics
• Suspicious server log entries → altinity-expert-clickhouse-logs