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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I suppose one could call that function using FALSE, and only use TRUE on error<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">OGRErr err = m_connection->GetOGRDataSource()->GetLayer(m_nIndex)->GetExtent(&e, FALSE);</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">If (</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">err</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">)<o:p></o:p></span></p>
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</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">err = m_connection->GetOGRDataSource()->GetLayer(m_nIndex)->GetExtent(&e, TRUE);</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Greg<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> fdo-internals-bounces@lists.osgeo.org [mailto:fdo-internals-bounces@lists.osgeo.org]
<b>On Behalf Of </b>Gabriele Monfardini<br>
<b>Sent:</b> Wednesday, March 26, 2014 9:57 AM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> [fdo-internals] Question about FDOOGRProvider<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">Hi all,</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">I had a PostgreSQL/Postgis database with some schemas and many tables.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">I'm connecting to it using MapGuide 2.5.2 (centos 6), OGR provider (FDO 3.8.0) and a recompiled gdal/ogr library to support PostgreSQL.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">All is working fine except for one thing.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">The first time that a map that use this db is opened it takes tens of seconds to appear.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">After the first time, the same map is opened in 3-4 seconds as it should.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">Investigating this issue the problem seems to be in schema discovery since purging cached schema information from maestro triggers again the slow start.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">Analyzing database log I've found that MapGuide seems to try to evaluate the extent of each geometry table in the database (brutally querying SELECT Extent(the_geom) on all
of them).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">And we happen to have a few very complicated views, defined from several other views, which are used in a totally unrelated project and never in MapGuide. Querying the extent
of those views eats a lot of seconds.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">Probably the called function is FdoByteArray* OgrSpatialContextReader::GetExtent() in OgrProvider.cpp.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">At line 664, in function <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif"">FdoByteArray* OgrSpatialContextReader::GetExtent() GetExtent from OGR library is called<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">/*OGRErr err =*/ m_connection->GetOGRDataSource()->GetLayer(m_nIndex)->GetExtent(&e, TRUE);</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">From OGR documentation the second parameter is a boolean called bForce<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Verdana","sans-serif";color:black;background:#FBFCFD">Returns the extent (MBR) of the data in the layer. If bForce is FALSE, and it would be expensive to establish the extent then OGRERR_FAILURE
will be returned indicating that the extent isn't know. If bForce is TRUE then some implementations will actually scan the entire layer once to compute the MBR of all the features in the layer.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">This seems to be the case in my situation, that evaluating the extent is expensive.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">From the code it does not seem to be any check to detect an OGRERR_FAILURE.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In your opinion (since I'm not familiar at all with FDO code) it would be feasible to pass bForce=false and maybe to cope with a possible failure?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Regards,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Gabriele Monfardini<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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