[processing] Ensure faster predicates are always tested first before slower predicates

nyalldawson · nyalldawson · commit c6565ef03a56 · 2020-01-03T05:25:33.000+10:00
Because we may be able to bypass the slower checks if the faster ones pass first
diff --git a/src/analysis/processing/qgsalgorithmjoinbylocation.cpp b/src/analysis/processing/qgsalgorithmjoinbylocation.cpp
@@ -133,6 +133,7 @@ QVariantMap QgsJoinByLocationAlgorithm::processAlgorithm( const QVariantMap &par
   const QStringList joinedFieldNames = parameterAsFields( parameters, QStringLiteral( "JOIN_FIELDS" ), context );
 
   mPredicates = parameterAsEnums( parameters, QStringLiteral( "PREDICATE" ), context );
+  sortPredicates( mPredicates );
 
   QString prefix = parameterAsString( parameters, QStringLiteral( "PREFIX" ), context );
 
@@ -303,6 +304,32 @@ bool QgsJoinByLocationAlgorithm::featureFilter( const QgsFeature &feature, QgsGe
   return ok;
 }
 
+void QgsJoinByLocationAlgorithm::sortPredicates( QList<int> &predicates )
+{
+  // Sort predicate list so that faster predicates are earlier in the list
+  // Some predicates in GEOS do not have prepared geometry implementations, and are slow to calculate. So if users
+  // are testing multiple predicates, make sure the optimised ones are always tested first just in case we can shortcut
+  // these slower ones
+
+  std::sort( predicates.begin(), predicates.end(), []( int a, int b ) -> bool
+  {
+    // return true if predicate a is faster than b
+
+    if ( a == 0 ) // intersects is fastest
+      return true;
+    else if ( b == 0 )
+      return false;
+
+    else if ( a == 5 ) // contains is fast for polygons
+      return true;
+    else if ( b == 5 )
+      return false;
+
+    // that's it, the rest don't have optimised prepared methods (as of GEOS 3.8)
+    return a < b;
+  } );
+}
+
 bool QgsJoinByLocationAlgorithm::processFeatures( QgsFeature &joinFeature, QgsProcessingFeedback *feedback )
 {
   if ( !joinFeature.hasGeometry() )
diff --git a/src/analysis/processing/qgsalgorithmjoinbylocation.h b/src/analysis/processing/qgsalgorithmjoinbylocation.h
@@ -67,6 +67,8 @@ class QgsJoinByLocationAlgorithm : public QgsProcessingAlgorithm
     std::unique_ptr< QgsFeatureSink > mUnjoinedFeatures;
     JoinMethod mJoinMethod = OneToMany;
     QList<int> mPredicates;
+
+    static void sortPredicates( QList<int > &predicates );
 };
 
 ///@endcond PRIVATE
