[teiid-issues] [JBoss JIRA] (TEIID-2381) Expanded source hint support

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-2381?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12765628#comment-12765628 ] 

Steven Hawkins commented on TEIID-2381:
---------------------------------------

>  Can you provide a specific example?

It's easier to illustrate with inline views:

SELECT /\*+ sh ... \*/ col1, col2 FROM (SELECT /\*+ sh ... \*/ col1 FROM t1) as v1, (SELECT /\*+ sh ... \*/ col2 FROM t2) as v2 WHERE col1 = col2

could be pushed as with the views removed as:

SELECT col1, col2 FROM t1, t2 WHERE col1 = col2

Do we accumulate source hints, or does the top level one take precedence?  

Or a scenario like:

SELECT /\*+ sh ... \*/ col1, col2 FROM (SELECT /\*+ sh ... \*/ col1 FROM t1, t2 ...) as v1, (SELECT /\*+ sh ... \*/ col2 FROM t3, t4 ...) as v2 WHERE col1 = col2

with pushdowns that cross the original view layers (t1 joined with t3 and t2 joined with t4).  Similar restructuring can happen with unions.  The main trust here is that the pre-optimization structure unless other hints to preserve views/joins are used does not give an indication of the final structure most of the time.  That is why the source hint was originally limited to simple query propagation and mainly targeted at the top-level query.

                
> Expanded source hint support
> ----------------------------
>
>                 Key: TEIID-2381
>                 URL: https://issues.jboss.org/browse/TEIID-2381
>             Project: Teiid
>          Issue Type: Enhancement
>          Components: Query Engine
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>         Attachments: HintsExecutionFactory.java, RandomExecutionFactory.java, RandomNumberStoredProcedureExecution.java, SysviewHintsExecutionTest.java
>
>
> We currently look at the source hint in only the root user query (not in subqueries nor the with clause) and only consider it in a very narrow set of circumstances when it's used in a view.

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