9.1.3 Set Membership in Storage Indexes

In Oracle Exadata System Software release 12.2.1.1.0, when data has been stored using the in-memory format columnar cache, Oracle Exadata Database Machine stores these columns compressed using dictionary encoding. For columns with fewer than 200 distinct values, the storage index creates a very compact in-memory representation of the dictionary and uses this compact representation to filter disk reads based on equality predicates. This feature is called set membership. A more limited filtering ability extends up to 400 distinct values.

For example, suppose a region of disk holds a list of customers in the United States and Canada. When you run a query looking for customers in Mexico, Oracle Exadata Storage Server can use the new set membership capability to improve the performance of the query by filtering out disk regions that do not contain customers from Mexico. In Oracle Exadata System Software releases earlier than 12.2.1.1.0, which do not have the set membership capability, a regular storage index would be unable to filter those disk regions.

Minimum requirements:

• Oracle Database 12c release 1 (12.1.0.2), minimum software version required is 12.1.0.2.161018DBBP or

• Oracle Database 12c release 2 (12.2.0.1)

• Patch for bug 24521608