Suboptimal Plan For Skewed Data In Partitioned Table
(Doc ID 2181526.1)
Last updated on SEPTEMBER 16, 2016
Applies to:Oracle Database - Enterprise Edition - Version 220.127.116.11 and later
Information in this document applies to any platform.
When the number of partitions in a table is 2*DoP or larger, then a PX PARTITION operation is selected instead of PX BLOCK operation. The PX PARTITION operation does not handle skewness well in the data. The extreme case is where a single partition contains all the data in which case the execution essentially runs serially with a single process reading all the data and the other slaves being idle.
Gathering statistics does not make any difference.
The following testcase demonstrates the issue:
To view full details, sign in with your My Oracle Support account.
Don't have a My Oracle Support account? Click to get started!
In this Document
|This document is being delivered to you via Oracle Support's Rapid Visibility (RaV) process and therefore has not been subject to an independent technical review.|