Unexpected Poor Execution Plan When Non-Popular Value Missing from Histogram
Last updated on NOVEMBER 04, 2016
Applies to:Oracle Database - Enterprise Edition - Version 18.104.22.168 to 22.214.171.124 [Release 11.2]
Information in this document applies to any platform.
A poor plan is chosen for predicates on certain columns.
For example, the majority of the time, the CBO chooses an INDEX UNIQUE SCAN on a primary key index, but for certain column values it will choose a less efficient INDEX RANGE SCAN on another index which contains the same leading columns contained within the primary key index.
SQLT report shows in Observation Section:
10053 trace will show:
Note: Buckets (Number of histograms) is less than NDV(Number of Distinct Values) for Frequency Histogram
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