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Limitations of the Oracle Cost Based Optimizer (Doc ID 212809.1)

Last updated on FEBRUARY 03, 2019

Applies to:

Oracle Database - Personal Edition - Version 7.1.4.0 and later
Oracle Database - Enterprise Edition - Version 6.0.0.0 and later
Oracle Database - Standard Edition - Version 7.0.16.0 and later
Information in this document applies to any platform.

Purpose

This Document outlines some of the limitations that may be encountered when using the Cost Based Optimizer.

Scope

Cost Based Optimizer Limitations

The Cost Based Optimizer (CBO) uses a complex and comprehensive model to choose the plan with the lowest cost overall. In most cases the model picks the best access methods for accessing the data in the most efficient manner. However, even with computed statistics and column histograms it is possible for the Cost Based Optimizer to choose a sub-optimal plan. There are limitations to the Cost model that can affect queries in some circumstances. Some of these are listed and explained below:

Details

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