Data node management

When a distributed hypertable is created, it will use all the available data nodes by default. It is possible, however, to use only a subset of data nodes with a particular distributed hypertable. This is useful to, e.g., tie a distributed hypertable to data nodes that have a specific performance profile.

To view the data nodes used by a distributed hypertable, use the following query:

SELECT hypertable_name, data_nodes
FROM timescaledb_information.hypertables
WHERE hypertable_name = 'conditions';

 hypertable_name |              data_nodes
-----------------+---------------------------------------
 conditions      | {data_node_1,data_node_2,data_node_3}

If you add additional data nodes to a database, they are not automatically associated with existing distributed hypertables. Instead, you need to explicitly attach a data node using attach_data_node:

SELECT add_data_node('node3', host => 'dn3.example.com');
SELECT attach_data_node('node3', hypertable => 'conditions');

When you attach a data node, the partitioning configuration of the distributed hypertable is also updated to account for the additional data node (the number of space partitions are automatically increased to match), unless the function parameter repartition is set to FALSE. The updated partitioning configuration ensures that the data node is able to take on newly created chunks.

In a similar way, if you want to remove a data node from a distributed hypertable, you can use detach_data_node.

SELECT detach_data_node('node1', hypertable => 'conditions');

Note that you cannot detach a data node that still holds data for the hypertable. To be able to detach a data node, ensure that either (1) all its data is deleted first, or (2) the data is replicated on other data nodes (see the next section on native replication).

Moving data between nodes

When you attach a new data node to a distributed hypertable, you might prefer to move data to the new node to free up storage on the existing nodes and make queries use the added capacity. Data can be moved between nodes at the chunk level:

CALL timescaledb_experimental.move_chunk('_timescaledb_internal._dist_hyper_1_1_chunk', 'data_node_3', 'data_node_2');

warning

The ability to move chunks between data nodes is an experimental feature that is under active development. We recommend that you do not use this feature in a production environment.

The move operation involves several transactions and therefore cannot be rolled back automatically. If a move operation fails, the failure is logged with an operation ID that later can be used to cleanup any state left on the involved nodes.

CALL timescaledb_experimental.cleanup_copy_chunk_operation('ts_copy_1_31');

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