My Oracle Support Banner

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 12.1.0.2 and later
Information in this document applies to any platform.

Symptoms

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:

 

Cause

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
Symptoms
Cause
Solution
References


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.
My Oracle Support provides customers with access to over a million knowledge articles and a vibrant support community of peers and Oracle experts.