10.7.3 Storage Index

Storage indexes are a very powerful capability provided in Oracle Exadata System Software that help avoid I/O operations. Oracle Exadata System Software creates and maintains a storage index in Exadata memory. The storage index keeps track of minimum and maximum values of columns per storage region for tables stored on that cell. This functionality is done transparently, and does not require any administration by the user.

When a query specifies a WHERE clause, Oracle Exadata System Software examines the storage index to determine if rows with the specified column value does not exist in a region of disk in the cell by comparing the column value to the minimum and maximum values maintained in the storage index. If the column value is outside the minimum and maximum range, then scan I/O in that region for that query is avoided. Many SQL operations run dramatically faster because large numbers of I/O operations are automatically replaced by a few in-memory lookups. To minimize operational overhead, storage indexes are created and maintained transparently and automatically by Oracle Exadata System Software.

Storage indexes provide benefits for encrypted tablespaces. However, storage indexes do not maintain minimum and maximum values for encrypted columns.