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https://issues.apache.org/jira/browse/HAWQ-492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15182071#comment-15182071
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Michael Andre Pearce (IG) commented on HAWQ-492:
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So i think for query predicate filtering i can see how we can do this.
e.g. where someone does SELECT * FROM table WHERE field < A
What want to try do is reduce having to return the full row if someone did:
SELECT fieldA fieldB FROM table.
as in we only return fieldA and fieldB and we only get this from the source
system, not forced to have to return all the fields from the source system.
Can you help point us at a document or sample that does this? If its supported.
> PXF Query Push-Down Feature enhancement to enable further push down to
> Datasource
> ---------------------------------------------------------------------------------
>
> Key: HAWQ-492
> URL: https://issues.apache.org/jira/browse/HAWQ-492
> Project: Apache HAWQ
> Issue Type: Improvement
> Components: PXF
> Reporter: Michael Andre Pearce (IG)
> Assignee: Lei Chang
>
> PXF currently supports push down of filters to the PXF plugin. So that PXF
> itself only needs to return the fields and rows that match the filters.
> Unfortunately it seems (and it could be simply miss-understanding) is done in
> a way where by the PXF plugin must retrieve the complete row/entry from the
> source then the filters are applied. With Query Filter Push-Down feature.
> With a JDBC PXF (https://github.com/kojec/pxf-field/tree/master/jdbc-pxf-ext)
> this seems to be the case where by the SELECT * FROM table is done.
> It would be much more efficient if the filter and fields are push down in a
> way so that the plugin can if in its use case can actually delegate that
> further down into datasource it is using, and retrieving and applying the
> filters needed to reduce the data it needs to be pulled back.
> As such the PXF accessor would be able to construct SELECT fieldA fieldB FROM
> table WHERE fieldA > 6
> It maybe that this is indeed possible, but looking at
> https://github.com/kojec/pxf-field/tree/master/jdbc-pxf-ext and the API's and
> documents currently available we cannot see a way to improve this jdbc pxf
> plugin to achieve this.
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