Apply patches from lightweight updates

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ALTER TABLE [db.]table [ON CLUSTER cluster] APPLY PATCHES [IN PARTITION partition_id]

The command manually triggers the physical materialization of patch parts created by lightweight UPDATE statements. It forcefully applies pending patches to the data parts by rewriting only the affected columns.

:::note

• It only works for tables in the MergeTree family (including replicated tables).
• This is a mutation operation and executes asynchronously in the background. :::

When to use APPLY PATCHES {#when-to-use}

:::tip Generally, you should not need to use APPLY PATCHES :::

Patch parts are normally applied automatically during merges when the apply_patches_on_merge setting is enabled (default). However, you may want to manually trigger patch application in these scenarios:

• To reduce the overhead of applying patches during SELECT queries
• To consolidate multiple patch parts before they accumulate
• To prepare data for backup or export with patches already materialized
• When apply_patches_on_merge is disabled and you want to control when patches are applied

Examples {#examples}

Apply all pending patches for a table:

ALTER TABLE my_table APPLY PATCHES;

Apply patches only for a specific partition:

ALTER TABLE my_table APPLY PATCHES IN PARTITION '2024-01';

Combine with other operations:

ALTER TABLE my_table APPLY PATCHES, UPDATE column = value WHERE condition;

Monitoring patch application {#monitor}

You can monitor the progress of patch application using the system.mutations table:

SELECT * FROM system.mutations
WHERE table = 'my_table' AND command LIKE '%APPLY PATCHES%';

See also {#see-also}

• Lightweight UPDATE - Create patch parts with lightweight updates
• apply_patches_on_merge setting - Control automatic patch application during merges