OGR JOIN performance problem on Linux

[Frank Warmerdam]

Dirk Jesko wrote:
> Hello,
>
> I have two machines running Apache 2 with MapServer 4.2.* (all necessary
> libraries are the current stable versions). One map server is running on
> Windows XP the other on Linux. Both systems contain the same data and
> mapfiles (besides the paths of course). One of the layers is an OGR
> connection to two shape files which are joined. One file contains
> approx. 200 rows with information the other approx. 30000 points with
> references to the information. The points are displayed. Both shapes
> have indexes associated (created separately on the according machine).
> While the join-query is very fast on Windows (it takes only a few
> seconds to display all points if the index is present), it takes ages on
> Linux (it makes no difference whether there is an index or not).
> Sometimes the web server even returns an error since the query takes to
> long. My guess would be that map server (resp. OGR) does not use the
> index on Linux.
>
> I would like to know whether someone observed a similar behavior and
> whether there is a possibility to speed up the query on Linux.

Dirk,

There is no *fundamental* reason the index shouldn't work as well on linux
as on windows.  Did you create the index on linux?  When you index a shapefile
a .idm file should be created with information on what indexes are in effect
and a .ind file with the actual indexes.  The .idm file is just XML.  Take a
look at it and verify that the information seems sensible ... particularly that
there is nothing funny about the filename used for the MIIDFilename.  You might
want to try making it an absolute path to the file.

The development and performance testing was done on Linux.

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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