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Parallel Update On Table Does Not Work If Statistics Have Been Calculated. (Doc ID 752816.1)

Last updated on FEBRUARY 18, 2019

Applies to:

Oracle Database - Enterprise Edition - Version 10.2.0.2 and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
That behavior affects 10.2.0.x (tested and reproduced from 10.2.0.2 to 10.2.0.4)


Symptoms

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Update doesn't use parallel option even if forced once statistics are collected


We can reproduce with following testcase:

Just setting foreign key deferred instead of immediate doesn't reproduce the behavior

Changes

So, summarizing. We have:
* A table with a deferrable constraint
-> If constraint is IMMEDIATE
** When updating constraint column, we expect no PDML as it happens
** When updating non-constraint column, we expect PDML to be used as it does before collecting stats.
** After collecting stats on this table, PDML is not being used despite we enforce with ALTER SESSION FORCE PARALLEL DML and hint.

-> If constraint is DEFERRABLE
** When updating constraint column, we expect no PDML as it happens
** When updating non-constraint column, we expect PDML to be used as it does before collecting stats.
** After collecting stats on this table, we expect PDML to be used as it does before collecting stats.

Cause

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In this Document
Symptoms
Changes
Cause
Solution
References

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