[teiid-issues] [JBoss JIRA] (TEIID-2245) Limit pushdown of nulls first/last

Fri Oct 5 09:36:03 EDT 2012

     [ https://issues.jboss.org/browse/TEIID-2245?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steven Hawkins resolved TEIID-2245.
-----------------------------------

         Assignee: Steven Hawkins  (was: Johnathon Lee)
    Fix Version/s: 8.2
                       (was: 7.4.5)
       Resolution: Done

Changed the default logic to not pushdown the default null order by default.  Rather there is a system property org.teiid.pushdownDefaultNullOrder that can be set to preserve the old behavior.

Also walked back the logic in ruleimplementjoinstrategy there is no issue with standard joins wrt consistent null ordering (that is even if we expect low and one or both sides is sorted high, then the results will still be correct).  The only times there would be an issue is if nulls were sorted inconsistently e.g. (a, null, a) - which no source should do or with except/intersect processing since nulls have equality there.  However we don't push down except/intersect sorts yet so we'll address that later.

To port this issue back, the affect of the patches can be further limited by just inlining the properties logic (rather than backporting the options logic) and by possibly leaving the nullorder manipulation in place in the ruleimplementjoinstrategy logic rather than moving it to rulecollapsesource.

> Limit pushdown of nulls first/last
> ----------------------------------
>
>                 Key: TEIID-2245
>                 URL: https://issues.jboss.org/browse/TEIID-2245
>             Project: Teiid
>          Issue Type: Enhancement
>          Components: Query Engine
>    Affects Versions: 7.4.4
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>            Priority: Critical
>             Fix For: 8.2
>
>
> By default Teiid will attempt to virtualize the default null order of nulls low.  This can have a negative impact on performance and is not needed in many situations.

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