postgres provider: avoid additional fetch after all features have already been processed

Author: jef-n

src/providers/postgres/qgspostgresfeatureiterator.cpp

@@ -35,6 +35,7 @@ QgsPostgresFeatureIterator::QgsPostgresFeatureIterator( QgsPostgresFeatureSource
     , mFetched( 0 )
     , mFetchGeometry( false )
     , mExpressionCompiled( false )
+    , mLastFetch( false )
 {
   if ( !source->mTransactionConnection )
   {
@@ -119,7 +120,7 @@ bool QgsPostgresFeatureIterator::fetchFeature( QgsFeature& feature )
   if ( mClosed )
     return false;
 
-  if ( mFeatureQueue.empty() )
+  if ( mFeatureQueue.empty() && !mLastFetch )
   {
     QString fetch = QString( "FETCH FORWARD %1 FROM %2" ).arg( mFeatureQueueSize ).arg( mCursorName );
     QgsDebugMsgLevel( QString( "fetching %1 features." ).arg( mFeatureQueueSize ), 4 );
@@ -145,6 +146,8 @@ bool QgsPostgresFeatureIterator::fetchFeature( QgsFeature& feature )
       if ( rows == 0 )
         continue;
 
+      mLastFetch = rows < mFeatureQueueSize;
+
       for ( int row = 0; row < rows; row++ )
       {
         mFeatureQueue.enqueue( QgsFeature() );
@@ -323,7 +326,6 @@ QString QgsPostgresFeatureIterator::whereClauseRect()
 bool QgsPostgresFeatureIterator::declareCursor( const QString& whereClause )
 {
   mFetchGeometry = !( mRequest.flags() & QgsFeatureRequest::NoGeometry ) && !mSource->mGeometryColumn.isNull();
-
 #if 0
   // TODO: check that all field indexes exist
   if ( !hasAllFields )
@@ -432,6 +434,7 @@ bool QgsPostgresFeatureIterator::declareCursor( const QString& whereClause )
     return false;
   }
 
+  mLastFetch = false;
   return true;
 }
 

src/providers/postgres/qgspostgresfeatureiterator.h

@@ -125,6 +125,7 @@ class QgsPostgresFeatureIterator : public QgsAbstractFeatureIteratorFromSource<Q
     virtual bool providerCanSimplify( QgsSimplifyMethod::MethodType methodType ) const override;
 
     bool mExpressionCompiled;
+    bool mLastFetch;
 };
 
 #endif // QGSPOSTGRESFEATUREITERATOR_H