[teiid-issues] [JBoss JIRA] (TEIID-1792) Inefficient plan using cartesian join

[Steven Hawkins (Resolved) (JIRA)]

     [ https://issues.jboss.org/browse/TEIID-1792?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steven Hawkins resolved TEIID-1792.
-----------------------------------

         Assignee: Steven Hawkins
    Fix Version/s: 7.6
                   7.4
       Resolution: Done


The root problem was that cardinality was missing on one of the join tables.  The unknown value prevented planning from determining the appropriate plan.

A change was made to join region scoring to ensure that in this case we do not issue cross joins of unknown size.

In general though it is not good to plan a query with a mixture of known and unknown cardinalities.
                
> Inefficient plan using cartesian join
> -------------------------------------
>
>                 Key: TEIID-1792
>                 URL: https://issues.jboss.org/browse/TEIID-1792
>             Project: Teiid
>          Issue Type: Bug
>          Components: Query Engine
>    Affects Versions: 7.4.1
>            Reporter: Debbie Steigner
>            Assignee: Steven Hawkins
>            Priority: Critical
>             Fix For: 7.6, 7.4
>
>
> We're trying to write a federated query, and we can't get Teiid to create an optimal plan. It is using a cartesian join, which causes Teiid to take a few hours and run out of memory, when we should be fetching a relatively small number of rows. We have tried using the new MAKEIND hint in 5.2, but Teiid seems to ignore it in this case. 
> See the SOA jura for more information.

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