Spotlight on Oracle 11.0 - Getting Started Guide

Global Trend Changes For Bottlenecks And Database Resources

Within Predictive Diagnostics, the procedure used to mark trend changes is covered in the topic Identify And Mark Trend Changes . There are two types of trend changes:

• Trend changes within SQL Performance apply only to the specified chart for the selected SQL statement.
• Trend changes within Impending Bottlenecks and Performance Modeling apply globally to ALL time-based charts for timed statistics and database resources.

The reason for this is the different scope for the different types of statistics.

• Predictions on the execution of SQL statements are specific to the SQL statements themselves. If one SQL statement will perform poorly on the Oracle database as data volumes and SQL execution rates increase, the same does not necessarily apply to other SQL statements. Equally, a SQL statement whose performance scales adequately with respect to one cost metric (CPU time, for example) may not scale adequately with respect to another (Disk Reads, for example).
• In contrast, a bottleneck or resource ceiling is likely to be a feature of the system itself and NOT depend specifically on the transactions in progress or the timed statistics used to analyze the system.