[mapguide-internals] Joining Oracle & SDF defect : Possible fix to validate

[Bruno Scott]

We had problem joining an sdf featureClass to an Oracle table using Autodesk
Oracle provider.
This problem was detected on 
  - MapGuide Enterprise 2009 SP1
  - MapGuide EnterPrise 2010
  - MapGuide OS 2.1 alpha ( with FDO from Enterprise 2010)
But it was working fine on
  - MapGuide Enterprise 2009
  - MapGuide OS 2.0 ( with FDO from Enterprise 2009 SP1)

I spended some time in debug to figure out what was happening.
First thing i found, there are 4 join algorythms and Mapguide choose the
proper one depending on the providers sorting capabilities
If both provider support sorting           then algo = sort-merge
If only first provider support sorting     then algo = nested loop join and
sorted block
If only second provider support sorting then algo = Batch Sorted Block
if both does not support sorting          then algo =  nested loop join

I was currious because i had a copy of my Oracle table in SHP format and
joining my shp to the same sdf was working fine.
Oracle joined to SDF is using the nested loop join and sorted block algo
and
SHP to SDF is using the nested loop join algo

So to test, i forced the use of the nested loop join for all joins.
Using this, Oracle->SDF join works.
I bet the reason for these 4 algo is performances related. So i decided to
investigate and try to find the problem in the nested loop join and sorted
block algo
I found that the sdfReader was closed just before an attemp to get the table
description, that was throwing a null reference exception.

In the GwsRightNestedLoopSortedBlockJoinQueryResults.cpp file
EGwsStatus CGwsRightNestedLoopSortedBlockJoinQueryResults::SetRelatedValues
(
    const GWSFeatureId & vals
)
{
    if (m_joinkeys == vals) {
        if (! m_neverusepooling) {
            // this completes features pool
            if (! m_bClosed) {
                while (ReadNext ())
                    ;
                //Close (); /* this should not be closed at this time, it
will be closed later */
            }
        }
        m_usepool = true;
        m_poolpos = -1;
        return eGwsOk;
    }
    m_pool->Reset ();
    m_usepool = false;
    m_poolpos = -1;

    return CGwsRightNestedLoopJoinQueryResults::SetRelatedValues (vals);
}

With that little Close() commented out the nested loop join and sorted block
algo works fine.
The SdfReader seems to be closed ok but i would need help from a GWS expert
to validate this fix because that code is not very easy to follow.

Another question, Now that i got both algo working, i timed both to check
the gain in performance.
Surprise! the nested loop join is faster (1.5 sec) than the nested loop join
and sorted block (2 sec). Should we use the nested loop join for that case?


Bruno Scott




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