[teiid-issues] [JBoss JIRA] (TEIID-2390) Improve xml/json production

[Steven Hawkins (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-2390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12783406#comment-12783406 ] 

Steven Hawkins commented on TEIID-2390:
---------------------------------------

It's fairly easy to convert the json handling for jsonobject/jsonarray so that their nested evaluations are done in the scope of the parent - but jsonarray_agg and jscon scalar subqueries would still be separate evaluations.  The same approach to xml is basically untenable as there are too many nesting combinations.  

With subqueries there is also the issue that evaluation will block and the whole intermediate result will be invalid and rebuilt with the next processing run.  Generally speaking all intermediate filestores should have better cleanup (when not used due to an exception or even when used, but never returned from the evaluator).

Will keep investigating.
                
> Improve xml/json production
> ---------------------------
>
>                 Key: TEIID-2390
>                 URL: https://issues.jboss.org/browse/TEIID-2390
>             Project: Teiid
>          Issue Type: Enhancement
>          Components: Query Engine
>            Reporter: Steven Hawkins
>            Assignee: Steven Hawkins
>             Fix For: 8.4.1
>
>
> The current xml/json logic can produce a lot of intermediate results that are recopied and can result in a slower performance for larger documents.  
> The logic could allow for nested evaluations to delay creating their full string forms or simply allow the return values to remain appendable rather than requiring full copies.

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