[mapguide-internals] PATCH: GwsQueryEngine chooses incorrect join algorithm for joins involving SDF/SHP sources

[Bruce Dechant]

Jackie,

The patch looks good.
This will be a big improvement when using SDF/SHP for joins - nice work!

Thanks,
Bruce

-----Original Message-----
From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Jackie Ng
Sent: Wednesday, December 14, 2011 9:00 AM
To: mapguide-internals at lists.osgeo.org
Subject: [mapguide-internals] PATCH: GwsQueryEngine chooses incorrect join algorithm for joins involving SDF/SHP sources

Hi All,

I have attached a patch for ticket #1888 (GwsQueryEngine evaluates incorrect join algorithm for joins involving SDF/SHP sources)

http://trac.osgeo.org/mapguide/ticket/1888

Simply put, the reason Feature Joins can perform really terrible for joins involving SDF or SHP files is because sortability is a critical factor in join algorithm selection, and under the existing code the SDF and SHP providers both fail the sortability check, which gives us the worst choices in join algorithms. 

This check is wrong because the two providers can actually output sorted query results via the FdoIExtendedSelect command, but that command only allows sorting on one property.

So the sortability check has been updated in this patch. A side of the join is now considered sortable if:

 1. It supports standard select ordering -OR-  2. It supports the FdoIExtendedSelect command (or
SdfIExtendedSelect/ShpIExtendedSelect) and we're only joining on one property.

The existing code already takes advantage of extended select w/ ordering if available so nothing needs to be done there.

Please review. Thanks

- Jackie

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