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Guidelines for Defining Oracle Rollback Segments

This topic is part of Configuring an Oracle Database for Siebel Applications.

NOTE:  The rollback segment concept has been replaced with the Undo tablespace, since Oracle 9i. However, customers can still use rollback segments if desired.

Rollback segments (RBS) may be used when a process is performing inserts, updates, or deletions (data manipulation language, or DML).

Oracle Database assigns each transaction to a rollback segment. As a rule of thumb, the total number of rollback segments required is based on four concurrent transactions per rollback segment. The DBA must monitor the database and configure rollback segments based on the requirements of the Siebel applications running.

Use the following guidelines to make sure there are sufficient rollback segments for large implementations:

• Create multiple rollback segments, each with multiple extents, at least, initially.
• Calculate 5-10 active transactions (user activity consisting of an insert, update, or deletion) per extent, and from 2-6 extents per rollback segment.

Use the following guidelines to make sure there are sufficient rollback segments for smaller implementations:

• Create a single, much larger rollback segment for Siebel Server components, such as Enterprise Integration Mgr (alias EIM), for Siebel EIM. Siebel Server components can point directly to this rollback segment when performing long-running queries.
• To promote optimal system performance, create your rollback segments in a dedicated table space on a dedicated disk. Rollback segments typically support high I/O rates, so this action improves system performance measurably.