Siebel Installation Guide for UNIX: Servers, Mobile Web Clients, Tools > Configuring the RDBMS > Configuring Oracle for Siebel Applications >

Guidelines for Defining Oracle Rollback Segments

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

Oracle assigns each transaction to a rollback segment. As a rule of thumb, the total number of rollback segments required should be based on four concurrent transactions per rollback segment. However, database administrators should monitor their 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.