About tablespaces

Tablespaces are used to determine the physical location of the tables and indexes in your database. 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.

Hypertables consist of a number of chunks, and each chunk can be located in a specific tablespace. This allows you to grow your hypertables across many disks. When you create a new chunk, a tablespace is automatically selected to store the chunk's data.

You can attach and detach tablespaces on a hypertable. When a disk runs out of space, you can detach the full tablespace from the hypertable, and than attach a tablespace associated with a new disk. To see the tablespaces for you hypertable, use the show_tablespaces command.

How hypertable chunks are assigned tablespaces

A hypertable can be partitioned in multiple dimensions, but only one of the dimensions is used to determine the tablespace assigned to a particular hypertable chunk. If a hypertable has one or more hash-partitioned, or space, dimensions, it uses the first hash-partitioned dimension. Otherwise, it uses the first time dimension.

This strategy ensures that hash-partitioned hypertables have chunks co-located according to hash partition, as long as the list of tablespaces attached to the hypertable remains the same. Modulo calculation is used to pick a tablespace, so there can be more partitions than tablespaces. For example, if there are two tablespaces, partition number three uses the first tablespace.

Hypertables that are only time-partitioned add new partitions continuously, and therefore have chunks assigned to tablespaces in a way similar to round-robin.

note

It is possible to attach more tablespaces than there are partitions for the hypertable. In this case, some tablespaces remain unused until others are detached or additional partitions are added. This is especially true for hash-partitioned tables.

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