[Qgis-developer] QGIS Server performance deterioration

[René-Luc Dhont]

Hi Devs,

I found which object is connected to QgsMapLayerRegistry through 
layerWasAdded slot in QGIS Server, and it's QgsEditorWidgetRegistry !

The method mapLayerAdded is apply to the layer added:
```
void QgsEditorWidgetRegistry::mapLayerAdded( QgsMapLayer* mapLayer )
{
   QgsVectorLayer* vl = qobject_cast<QgsVectorLayer*>( mapLayer );

   if ( vl )
   {
     connect( vl, SIGNAL( readCustomSymbology( const QDomElement&, 
QString& ) ), this, SLOT( readSymbology( const QDomElement&, QString& ) ) );
     connect( vl, SIGNAL( writeCustomSymbology( QDomElement&, 
QDomDocument&, QString& ) ), this, SLOT( writeSymbology( QDomElement&, 
QDomDocument&, QString& ) ) );
   }
}
```

Could a method call `mapLayerWillBeRemoved` be added ?


Le 07/06/2016 15:58, René-Luc Dhont a écrit :
> Hi devs,
>
> David Marteau, our colleague in 3Liz, has found some serious 
> deteriorations of performance in QGIS Server.
>
> The first one concerne QgsExpressionContext which is not clean up in 
> QgsServer::handleRequest
>
> Each call to QgsMapLayer::draw add items to QgsExpressionContext scope.
> The scope is not cleaned between request and thus the scope list to 
> grow indefinitely.
>
> Having the list growing indefinitely deteriorate seriously 
> performances in the long run. It also increase the memory footprint 
> but in a less noticiable way.
>
> This behavior has been checked by monitoring reponse time of several 
> ten of thousand identical requests during server long runs.
>
> This has been fixed in master and in LTR:
> https://github.com/qgis/QGIS/commit/5c3aa51e80887de6ff76682a42814041bb32cd5b 
>
> https://github.com/qgis/QGIS/commit/50181eee00709e3f7e29b2b53282f28bdedfe265 
>
>
> Now we encounter an other issue with deteriorationof performance in 
> QGIS Server.
>
> This issue is due to the slot 'layerWasAdded' in QgsMapLayerRegistry. 
> The duration of the emit layerWasAdded grows with the number of 
> drawing. Do you know what it is done when 'layerWasAdded' is emitted ?
>
> Regards,
> René-Luc D'Hont
> 3Liz