[teiid-issues] [JBoss JIRA] Commented: (TEIID-1474) Add query hint to limit parallel execution of union members

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-1474?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583064#comment-12583064 ] 

Steven Hawkins commented on TEIID-1474:
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To round out the proposal:

Would the hint also affect joins to force serial execution?

Can the hint appear anywhere above the union (through 1 or more view layers), or would it have to be located on the union query? 

What heuristics would we apply to determine the firing order of branches?



> Add query hint to limit parallel execution of union members
> -----------------------------------------------------------
>
>                 Key: TEIID-1474
>                 URL: https://issues.jboss.org/browse/TEIID-1474
>             Project: Teiid
>          Issue Type: Feature Request
>            Reporter: Howard Abrams
>            Assignee: Steven Hawkins
>
> We would like a new query hint to limit the number of parallel executions of union members. This is useful in two situations:
> 1. When the queries are expensive, but the overall union contains a limit that is most likely to be fulfilled by the first member of the union
> 2. When the queries are backed by a common resource which may be overloaded by multiple queries
> The addition of a hint would make this manageable by the client; perhaps something like "/*+ parallel=2*/"? 

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