Limitations of the Oracle Cost Based Optimizer
(Doc ID 212809.1)
Last updated on MARCH 15, 2021
Applies to:Oracle Database - Personal Edition - Version 184.108.40.206 and later
Oracle Database - Enterprise Edition - Version 220.127.116.11 and later
Oracle Database - Standard Edition - Version 18.104.22.168 and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.
This Document outlines some of the limitations that may be encountered when using the Cost Based Optimizer.
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:
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