Parallel Queries in 12c Spending Time on Recursive Query With /* DS_SKEW */ (Doc ID 2104350.1)

Last updated on SEPTEMBER 19, 2017

Applies to:

Oracle Database - Enterprise Edition - Version 12.1.0.2 and later
Information in this document applies to any platform.

Symptoms

Some parallel queries seems to be stuck at when degree of parallelism is increased beyond 6 in 12c. Parallel 6 works without any problem, query completes in 2.5 seconds, parallel 8 and query doesn't complete after hours. With higher degree internal dynamic sampling query with /* DS_SKEW */ was taking long time to complete.

The query can be found to be as:

 

Same query was working fine before 12c upgrade.

Changes

 Database upgraded from 10.2.0.5 to 12.10.2

Cause

Sign In with your My Oracle Support account

Don't have a My Oracle Support account? Click to get started

My Oracle Support provides customers with access to over a
Million Knowledge Articles and hundreds of Community platforms