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hologres_table_group

  • In Hologres, data is stored in shards on pangu

  • Table groups are logical storage units used to manage shards

  • Each table group contains a fixed number of shards

  • When a table is created:

NOTE

A table group is a unique concept in Hologres and differs from PostgreSQL's tablespace (which identifies storage locations)

Layout of table groups

Key Relationships​

Table Groups and Schemas​

Tables in different schemas can belong to the same table group, sharing the same underlying shards

Table Groups and Databases​

  • A database contains one or more table groups
  • By default, Hologres creates one table group per database, but you can add more or modify the default

Table Groups and Shards​

  • Shards are not shared between table groups
  • Each shard has a unique ID within an instance

Shard Count​

  • The number of shards in a table group is fixed at creation and cannot be changed later
  • To change the shard count, you must create a new table group

Tables and Shards​

  • Data in a table is distributed to shards based on the distribution key
  • Without a distribution key, data is randomly allocated

Table Groups and Tables​

  • Multiple tables can belong to the same table group, but a table cannot belong to multiple table groups.
  • Tables cannot be moved to another table group unless re-created or moved using a specific function.

References