[teiid-issues] [JBoss JIRA] (TEIID-2253) Multi-source issues

[Steven Hawkins (JIRA)]

     [ https://issues.jboss.org/browse/TEIID-2253?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steven Hawkins resolved TEIID-2253.
-----------------------------------

    Fix Version/s: 8.3
       Resolution: Done


Marking the parent issue as resolved, as we will not look to address TEIID-2251 anytime soon.  Thus TEIID-2251 will serve as a KI and discussion focus.

The changes greatly rationalized the multi-source feature.  It is now also a primary concern of the engine and thus optimization aware rather than being a simplistic override.  

If the org.teiid.implicitMultiSourceJoin is set to false, then feature forces the user to specify explicit join criteria, which ensures the results will be as expected.  

The old logic (and the current logic with implicit joins) suffers from not properly partitioning results if a join between to multi-source tables from the same model is not pushed down - which can happen for a variety of reasons (for example unsupported join criteria).

The possibly breaking changes here are:
1. The multi-source column is now a pseudo column and is not selectable in wildcards.  This seems to be an oversight of the old feature since we lacked the differentiation between a pseudo column and something that was non-selectable (which would have prevented it's use at all in projection).
2. Multi-source inserts cannot be broadcast to all sources, rather they must target a single source.  This is consistent with the partitioned view logic and logically follows since multi-source is functioning on a sharding not replication premise.
                
> Multi-source issues
> -------------------
>
>                 Key: TEIID-2253
>                 URL: https://issues.jboss.org/browse/TEIID-2253
>             Project: Teiid
>          Issue Type: Enhancement
>          Components: Query Engine
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>             Fix For: 8.3
>
>
> The design of the multi-source feature has several issues that need addressed.

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