Altinity Expert Clickhouse Mutations

Mutation Tracking and Analysis

Track and diagnose ALTER UPDATE, ALTER DELETE, and other mutation operations.

Diagnostics

Run all queries from checks.sql in this skill's directory and analyze the results.

Problem Investigation

Why Is Mutation Stuck?

Check for competing operations using these ad-hoc queries:

-- Active merges on same table
select
    database,
    table,
    is_mutation,
    elapsed,
    progress,
    num_parts
from system.merges
where database = '{database}' and table = '{table}'

-- Replication queue for same table
select
    type,
    create_time,
    is_currently_executing,
    num_tries,
    last_exception
from system.replication_queue
where database = '{database}' and table = '{table}'
order by create_time
limit 20

-- Part mutations status
select
    name,
    active,
    mutation_version,
    modification_time
from system.parts
where database = '{database}' and table = '{table}'
order by mutation_version desc
limit 30

Canceling Mutations

To kill a stuck mutation:

-- Find mutation_id first
select mutation_id, command from system.mutations
where database = '{database}' and table = '{table}' and not is_done;

-- Then kill it
-- KILL MUTATION WHERE database = '{database}' AND table = '{table}' AND mutation_id = '{mutation_id}';

Warning: Killed mutations leave table in partially-mutated state.

Best Practices

Mutation Anti-Patterns

Monitoring Mutations

Set alerts for:

• Mutations pending > 10
• Mutation age > 1 hour
• latest_fail_reason not empty

Cross-Module Triggers

Settings Reference