Understanding Data Storage

Oracle OLAP multidimensional data is stored in analytic workspaces. An analytic workspace can contain a variety of objects, such as dimensions, variables (also called measures), and OLAP DML programs. These objects typically support a particular application or set of data.

Whenever an analytic workspace is created, modified, or accessed, the information is stored in tables in the relational database.

User-Owned Tables

An analytic workspace is stored in a table in the Oracle database as a Binary Large Object (BLOB).

For example, if the SCOTT user creates two analytic workspaces, one named SALESDATA and the other named SALESPRGS, then these tables will be created in the SCOTT schema:

AW$SALESDATA

AW$SALESPRGS

These tables store all of the object definitions and data for these analytic workspaces.

System Tables

The SYS user owns several tables associated with analytic workspaces:

AW$EXPRESS

AW$

PS$

AW$EXPRESS stores the express analytic workspace. This workspace contains objects and programs that support the OLAP DML. The express workspace is used any time that a session is open.

AW$ maintains a record of all analytic workspaces in the database, recording its name, owner, and other information.

PS$ maintains a history of all page spaces. A page is an ordered series of bytes equivalent to a file. Oracle OLAP manages a cache of workspace pages. Pages are read from storage in a table and written into the cache in response to a query. The same page can be accessed by several sessions.

One writer and many readers can use an analytic workspace at one time. The information stored in PS$ enables the Oracle OLAP to discard pages that are no longer in use, and to maintain a consistent view of the data for all users, even when the workspace is being modified during their sessions. When changes to a workspace are saved, unused pages are purged and the corresponding rows are deleted from PS$.