Move data for data tiering

PostgreSQL uses tablespaces to determine the physical location of your data. In most cases, you want to use faster storage to store data that is accessed frequently, and slower storage for data that is accessed less often.

In TimescaleDB, you can move chunks between different tablespaces using the move_chunk API call.

note

You must be logged in as a super user, such as the postgres user, to use the move_chunk() API call.

Move data

To set up data tiering, you first need to create the new tablespace and set the storage mount point. You can then use the move_chunk API call to move individual chunks from the default tablespace to the new tablespace. The move_chunk command also allows you to move indexes belonging to those chunks to an approprate tablespace.

Additionally, move_chunk allows you reorder the chunk during the migration. This can be used to make your queries faster, and works in a similar way to the reorder_chunk command.

Moving data

  1. Create a new tablespace. In this example, the tablespace is called history, it is owned by the postgres super user, and the mount point is /mnt/history:
    CREATE TABLESPACE history
    OWNER postgres
    LOCATION '/mnt/history';
  2. List chunks that you want to move. In this example, chunks that contain data that is older than two days:
    SELECT show_chunks('conditions', older_than => INTERVAL '2 days');
  3. Move a chunk and its index to the new tablespace. You can also reorder the data in this step. In this example, the chunk called _timescaledb_internal._hyper_1_4_chunk is moved to the history tablespace, and is reordered based on its time index:
    SELECT move_chunk(
      chunk => '_timescaledb_internal._hyper_1_4_chunk',
      destination_tablespace => 'history',
      index_destination_tablespace => 'history',
      reorder_index => '_timescaledb_internal._hyper_1_4_chunk_netdata_time_idx',
      verbose => TRUE
    );
  4. You can verify that the chunk now resides in the correct tablespace by querying pg_tables to list all of the chunks on the tablespace:
    SELECT tablename from pg_tables
      WHERE tablespace = 'history' and tablename like '_hyper_%_%_chunk';
    You can also verify that the index is in the correct location:
    SELECT indexname FROM pg_indexes WHERE tablespace = 'history';

Move data in bulk

To move several chunks at once, select the chunks you want to move by using FROM show_chunks(...). For example, to move chunks containing data between 1 and 3 weeks old, in a hypertable named example:

SELECT move_chunk(
  chunk => i, 
  destination_tablespace => '<TABLESPACE>') 
FROM show_chunks('example', now() - INTERVAL '1 week', now() - INTERVAL '3 weeks') i;

Examples

After moving a chunk to a slower tablespace, you can move it back to the default, faster tablespace:

SELECT move_chunk(
  chunk => '_timescaledb_internal._hyper_1_4_chunk',
  destination_tablespace => 'pg_default',
  index_destination_tablespace => 'pg_default',
  reorder_index => '_timescaledb_internal._hyper_1_4_chunk_netdata_time_idx'
);

You can move a data chunk to the slower tablespace, but keep the chunk's indexes on the default, faster tablespace:

SELECT move_chunk(
  chunk => '_timescaledb_internal._hyper_1_4_chunk',
  destination_tablespace => 'history',
  index_destination_tablespace => 'pg_default',
  reorder_index => '_timescaledb_internal._hyper_1_4_chunk_netdata_time_idx'
);

You can also keep the data in pg_default but move the index to history. Alternatively, you can set up a third tablespace called history_indexes, and move the data to history and the indexes to history_indexes.

In TimescaleDB 2.0 and later, you can use move_chunk with the job scheduler framework. For more information, see the user-defined actions section.

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