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ON CLUSTER is not valid for KILL MUTATION, and will result in an exception. Correcting the docs for this syntax
142 lines
4.4 KiB
Markdown
142 lines
4.4 KiB
Markdown
---
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slug: /en/sql-reference/statements/kill
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sidebar_position: 46
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sidebar_label: KILL
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title: "KILL Statements"
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---
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There are two kinds of kill statements: to kill a query and to kill a mutation
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## KILL QUERY
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``` sql
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KILL QUERY [ON CLUSTER cluster]
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WHERE <where expression to SELECT FROM system.processes query>
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[SYNC|ASYNC|TEST]
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[FORMAT format]
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```
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Attempts to forcibly terminate the currently running queries.
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The queries to terminate are selected from the system.processes table using the criteria defined in the `WHERE` clause of the `KILL` query.
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Examples:
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First, you'll need to get the list of incomplete queries. This SQL query provides them according to those running the longest:
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List from a single ClickHouse node:
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``` sql
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SELECT
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initial_query_id,
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query_id,
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formatReadableTimeDelta(elapsed) AS time_delta,
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query,
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*
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FROM system.processes
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WHERE query ILIKE 'SELECT%'
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ORDER BY time_delta DESC;
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```
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List from a ClickHouse cluster:
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``` sql
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SELECT
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initial_query_id,
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query_id,
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formatReadableTimeDelta(elapsed) AS time_delta,
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query,
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*
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FROM clusterAllReplicas(default, system.processes)
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WHERE query ILIKE 'SELECT%'
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ORDER BY time_delta DESC;
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```
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Kill the query:
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``` sql
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-- Forcibly terminates all queries with the specified query_id:
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KILL QUERY WHERE query_id='2-857d-4a57-9ee0-327da5d60a90'
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-- Synchronously terminates all queries run by 'username':
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KILL QUERY WHERE user='username' SYNC
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```
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:::tip
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If you are killing a query in ClickHouse Cloud or in a self-managed cluster, then be sure to use the ```ON CLUSTER [cluster-name]``` option, in order to ensure the query is killed on all replicas
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:::
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Read-only users can only stop their own queries.
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By default, the asynchronous version of queries is used (`ASYNC`), which does not wait for confirmation that queries have stopped.
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The synchronous version (`SYNC`) waits for all queries to stop and displays information about each process as it stops.
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The response contains the `kill_status` column, which can take the following values:
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1. `finished` – The query was terminated successfully.
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2. `waiting` – Waiting for the query to end after sending it a signal to terminate.
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3. The other values explain why the query can’t be stopped.
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A test query (`TEST`) only checks the user’s rights and displays a list of queries to stop.
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## KILL MUTATION
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The presence of long-running or incomplete mutations often indicates that a ClickHouse service is running poorly. The asynchronous nature of mutations can cause them to consume all available resources on a system. You may need to either:
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- Pause all new mutations, `INSERT`s , and `SELECT`s and allow the queue of mutations to complete.
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- Or manually kill some of these mutations by sending a `KILL` command.
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``` sql
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KILL MUTATION
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WHERE <where expression to SELECT FROM system.mutations query>
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[TEST]
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[FORMAT format]
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```
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Tries to cancel and remove [mutations](../../sql-reference/statements/alter/index.md#alter-mutations) that are currently executing. Mutations to cancel are selected from the [`system.mutations`](../../operations/system-tables/mutations.md#system_tables-mutations) table using the filter specified by the `WHERE` clause of the `KILL` query.
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A test query (`TEST`) only checks the user’s rights and displays a list of mutations to stop.
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Examples:
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Get a `count()` of the number of incomplete mutations:
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Count of mutations from a single ClickHouse node:
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``` sql
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SELECT count(*)
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FROM system.mutations
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WHERE is_done = 0;
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```
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Count of mutations from a ClickHouse cluster of replicas:
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``` sql
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SELECT count(*)
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FROM clusterAllReplicas('default', system.mutations)
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WHERE is_done = 0;
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```
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Query the list of incomplete mutations:
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List of mutations from a single ClickHouse node:
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``` sql
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SELECT mutation_id, *
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FROM system.mutations
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WHERE is_done = 0;
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```
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List of mutations from a ClickHouse cluster:
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``` sql
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SELECT mutation_id, *
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FROM clusterAllReplicas('default', system.mutations)
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WHERE is_done = 0;
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```
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Kill the mutations as needed:
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``` sql
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-- Cancel and remove all mutations of the single table:
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KILL MUTATION WHERE database = 'default' AND table = 'table'
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-- Cancel the specific mutation:
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KILL MUTATION WHERE database = 'default' AND table = 'table' AND mutation_id = 'mutation_3.txt'
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```
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The query is useful when a mutation is stuck and cannot finish (e.g. if some function in the mutation query throws an exception when applied to the data contained in the table).
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Changes already made by the mutation are not rolled back.
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