lightweight_* session settings

ClickHouse session settings in the lightweight_* generated group.

These settings are available in system.settings and are autogenerated from source.

lightweight_delete_mode

A mode of internal update query that is executed as a part of lightweight delete.

Possible values:

• alter_update - run ALTER UPDATE query that creates a heavyweight mutation.
• lightweight_update - run lightweight update if possible, run ALTER UPDATE otherwise.
• lightweight_update_force - run lightweight update if possible, throw otherwise.

For DELETE FROM ... ON CLUSTER, each executing host derives the mode from its own settings, so hosts whose profiles set different defaults can run the delete in different modes. A replicated shard executes on one replica, so there it is that replica’s settings that decide. Setting it in the session of the initiating query overrides this, because the distributed DDL entry carries session changes at distributed_ddl_entry_format_version 2 and above, which the default satisfies. A host that constrains the setting clamps the value back.

lightweight_deletes_sync

The same as mutations_sync, but controls only execution of lightweight deletes.

Possible values:

Value	Description
0	Mutations execute asynchronously.
1	The query waits for the lightweight deletes to complete on the current server.
2	The query waits for the lightweight deletes to complete on all replicas (if they exist).
3	The query waits only for the active replicas. Inactive replicas apply the lightweight deletes when they become active.

See Also

• Synchronicity of ALTER Queries
• Mutations

Cloud default value: 1.