Manage mutations

Mutations change existing table parts. They run asynchronously and use server resources while they process data.

Before you begin

• Use the analytics database. Create it with the database API if it does not exist.
• Use an events table with enough rows for projection materialization to remain active.

1. Add a projection

A materialized projection creates a mutation for existing parts.

ALTER TABLE events ADD PROJECTION by_tenant (SELECT `__raw_data.tenant`, count() GROUP BY `__raw_data.tenant`)

2. Materialize the projection

Start the projection materialization.

ALTER TABLE events MATERIALIZE PROJECTION by_tenant

3. Inspect mutations

Read the mutation ID and status from system.mutations.

SELECT mutation_id, command, is_done, is_killed FROM system.mutations WHERE database = currentDatabase() AND table = 'events'

4. Cancel active mutations

Cancel unfinished mutations for events. Add the mutation_id condition to target one mutation.

KILL MUTATION WHERE table = 'events'

Check the result

Inspect system.mutations after the request. The row shows whether the mutation is complete or marked as killed.

Next steps

• Mutation concepts
• KILL MUTATION statements