atoti.Hierarchy.virtual

property Hierarchy.virtual: bool | None

Whether the hierarchy is virtual or not.

A virtual hierarchy does not store in memory the list of its members. Hierarchies with large cardinality are good candidates for being virtual.

By default, a given hierarchy is automatically set as virtual if and only if it comes from an ExternalTable and one of the following conditions is met:

• The hierarchy has a cardinality of 10000 or more;

• The activeviam.experimental.forceVirtualHierarchies property is set to true.

Note

As its name suggests, activeviam.experimental.forceVirtualHierarchies is an experimental/temporary property which may change in future bugfix releases.

Example

>>> from atoti_directquery_clickhouse import ConnectionConfig, TableConfig
>>> connection_config = ConnectionConfig(
...     url=f"clickhouse:http://localhost:{clickhouse_server_port}/{schema_name}",
... )
>>> table_config = TableConfig(keys={"id"})

• Without activeviam.experimental.forceVirtualHierarchies:

  >>> session = tt.Session.start()
  >>> external_database = session.connect_to_external_database(
  ...     connection_config
  ... )
  >>> sales_table = session.add_external_table(
  ...     external_database.tables["sales"], config=table_config
  ... )
  >>> cube = session.create_cube(sales_table)
  >>> cube.hierarchies["product"].virtual
  False
  

• With activeviam.experimental.forceVirtualHierarchies:

  >>> session_config = tt.SessionConfig(
  ...     java_options=["-Dactiveviam.experimental.forceVirtualHierarchies=true"]
  ... )
  >>> session = tt.Session.start(session_config)
  >>> external_database = session.connect_to_external_database(
  ...     connection_config
  ... )
  >>> sales_table = session.add_external_table(
  ...     external_database.tables["sales"], config=table_config
  ... )
  >>> cube = session.create_cube(sales_table)
  >>> cube.hierarchies["product"].virtual
  True