SYSTEM Queries

Managing Distributed Tables

ClickHouse can manage distributed tables. When a user inserts data into these tables, ClickHouse first creates a queue of the data that should be sent to cluster nodes, then asynchronously sends it. You can manage queue processing with the STOP DISTRIBUTED SENDS, FLUSH DISTRIBUTED, and START DISTRIBUTED SENDS queries. You can also synchronously insert distributed data with the insert_distributed_sync setting.

STOP DISTRIBUTED SENDS

Disables background data distribution when inserting data into distributed tables.

SYSTEM STOP DISTRIBUTED SENDS [db.]<distributed_table_name>

FLUSH DISTRIBUTED

Forces ClickHouse to send data to cluster nodes synchronously. If any nodes are unavailable, ClickHouse throws an exception and stops query execution. You can retry the query until it succeeds, which will happen when all nodes are back online.

SYSTEM FLUSH DISTRIBUTED [db.]<distributed_table_name>

START DISTRIBUTED SENDS

Enables background data distribution when inserting data into distributed tables.

SYSTEM START DISTRIBUTED SENDS [db.]<distributed_table_name>