[gdal-dev] double delay getting feature count

[Chaitanya kumar CH]

Bruce,

You can take a look at the GDAL/OGR's Oracle driver code at
http://trac.osgeo.org/gdal/browser/branches/1.6/gdal/ogr/ogrsf_frmts/oci
Take a look at the implementation of the function at
http://trac.osgeo.org/gdal/browser/branches/1.6/gdal/ogr/ogrsf_frmts/oci/ogrocitablelayer.cpp#L1189

Unless you are using a filter for that layer, it is executing another SQL
command.

On Thu, Oct 15, 2009 at 1:12 AM, Clay, Bruce <bclay at ball.com> wrote:

>  Chaitany:
>
>
>
> Thanks for your reply.
>
>
>
>   I would expect to get one delay due to the connection time but I did not
> expect one for both the GetFeatureCount and the GetNextFeature.  Both of
> those calls are on the same layer variable.  I originally had the
> GetFeatureCount before the ResetReading.  That gave the same delay. As it
> turned out the code show below actually had 3 delays.  One for the
> GetNextFeature outside the loop, one for the GetFeatureCount and another one
> for the first encounter of the GetNextFeature at the bottom of the loop.
> Apparently the GetFeatureCount is leaving the feature pointer at the bottom
> of the loop and we have to take time to move back to the top.
>
>
>
> I would step into the code but I can’t get Visual Studio to dig down into
> gdal16.dll for some reason even though it was built as a debug library.
>
>
>
>
>
> Bruce
>  ------------------------------
>
> *From:* Chaitanya kumar CH [mailto:chaitanya.ch at gmail.com]
> *Sent:* Wednesday, October 14, 2009 2:34 PM
> *To:* Clay, Bruce
> *Cc:* gdal-dev at lists.osgeo.org
> *Subject:* Re: [gdal-dev] double delay getting feature count
>
>
>
> Bruce,
>
> The GetFeatureCount function gets the value with an SQL query to the data
> server. The bottleneck may be at the connection.
>
> On Wed, Oct 14, 2009 at 9:28 PM, Clay, Bruce <bclay at ball.com> wrote:
>
> I have tried several different arrangements trying to get the feature count
> from a user selection and I am getting a delay two times for each query.
>
>
>
> My current arrangement is
>
>
>
> OGRLayer *queryLayer = dataSource->ExecuteSQL(fullQueryString, NULL,
> "generic");
>
>
>
> if (queryLayer != NULL)
>
> {
>
>       queryLayer->ResetReading();
>
>       OGRFeature *feature = queryLayer->GetNextFeature();
>
>
>
>       int numFeatures = queryLayer->GetFeatureCount();
>
>
>
> . . .Display progress meter then loop reading the features from Oracle
>
>
>
>
>
>
>
>
>
> I have tried putting the call to GetFeatureCount first and there is no
> apparent difference.
>
>
>
> I am reading data from an Oracle database and using GDAL version 1.6.2 on
> Windows XP
>
>
>
> The call to ExecuteSql returns right away but the call to the first
> GetNextFeature and the call to GetFeatureCount both have a long delay
> depending on the size of the dataset.
>
>
>
> I need the feature count to use in a progress popup window to let the user
> know what is happening.
>
>
>
> Is there a way to only pay for the query time once and still get the
> feature count?
>
>
>
>
>
> Bruce
>
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>
>
>
> --
> Best regards,
> Chaitanya kumar CH.
>
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> notify the sender by email if you are not the intended recipient.  If you are
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>
>


-- 
Best regards,
Chaitanya kumar CH.
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