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

Last updated on AUGUST 26, 2021

Applies to:

Oracle Database - Enterprise Edition - Version 12.1.0.2 and later
Oracle Database Cloud Schema Service - Version N/A and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A 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

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In this Document
Symptoms
Changes
Cause
Solution
References


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