diff --git a/common/plugins/eu.esdihumboldt.hale.common.align/help/join.xhtml b/common/plugins/eu.esdihumboldt.hale.common.align/help/join.xhtml
index ff307988a6..7c37412f6c 100644
--- a/common/plugins/eu.esdihumboldt.hale.common.align/help/join.xhtml
+++ b/common/plugins/eu.esdihumboldt.hale.common.align/help/join.xhtml
@@ -42,6 +42,19 @@
 		</div>
 		<p>To create a condition, select a property on the left and on the
 			right side, then click on the button in the middle.</p>
+			
+		<h2>
+			<a name="condition">Index Join Handler (experimental)</a>
+		</h2>
+		<p>
+			To activate the use of the Index Join Handler for all Join and Groovy
+			Join transformations, set the Java system property <code>hale.functions.use_index_join_handler</code>
+			or the environment variable <code>HALE_FUNCTIONS_USE_INDEX_JOIN_HANDLER</code>.
+		</p>
+		<p>
+			The Index Join Handler is experimental and can potentially have a
+			negative impact on the performance of Join and Groovy Join transformations.
+		</p>
 	</div>
 </body>
 </html>
\ No newline at end of file
diff --git a/common/plugins/eu.esdihumboldt.hale.common.align/help/merge/help.xhtml b/common/plugins/eu.esdihumboldt.hale.common.align/help/merge/help.xhtml
index a5993c76b8..5ce7278984 100644
--- a/common/plugins/eu.esdihumboldt.hale.common.align/help/merge/help.xhtml
+++ b/common/plugins/eu.esdihumboldt.hale.common.align/help/merge/help.xhtml
@@ -20,6 +20,20 @@
 	</br>
 		<img src="../../eu.esdihumboldt.hale.common.align/help/merge/mergeAggregate.png" />
 	</p>
+
+	<h2>
+		<a name="condition">Index Merge Handler (experimental)</a>
+	</h2>
+	<p>
+		To activate the use of the Index Merge Handler for all Merge and Groovy
+		Merge transformations, set the Java system property <code>hale.functions.use_index_merge_handler</code>
+		or the environment variable <code>HALE_FUNCTIONS_USE_INDEX_MERGE_HANDLER</code>.
+	</p>
+	<p>
+		The Index Merge Handler is experimental and can potentially have a
+		negative impact on the performance of Merge and Groovy Merge transformations.
+	</p>
+	
 </div>
 </body>
 </html>
diff --git a/cst/plugins/eu.esdihumboldt.cst.functions.core/META-INF/MANIFEST.MF b/cst/plugins/eu.esdihumboldt.cst.functions.core/META-INF/MANIFEST.MF
index e55e9d6355..50f73fbe6a 100644
--- a/cst/plugins/eu.esdihumboldt.cst.functions.core/META-INF/MANIFEST.MF
+++ b/cst/plugins/eu.esdihumboldt.cst.functions.core/META-INF/MANIFEST.MF
@@ -9,6 +9,7 @@ Require-Bundle: eu.esdihumboldt.hale.common.align;bundle-version="2.2.0",
 Import-Package: com.google.common.base;version="9.0.0",
  com.google.common.collect,
  de.fhg.igd.osgi.util;version="1.0.0",
+ de.fhg.igd.slf4jplus,
  eu.esdihumboldt.hale.common.convert,
  eu.esdihumboldt.hale.common.core,
  eu.esdihumboldt.hale.common.core.io,
@@ -34,6 +35,7 @@ Import-Package: com.google.common.base;version="9.0.0",
  eu.esdihumboldt.util.groovy.paths,
  net.jcip.annotations,
  org.locationtech.jts.geom;version="1.13.0",
+ org.slf4j;version="1.7.36",
  org.springframework.core.convert;version="5.2.0"
 Export-Package: eu.esdihumboldt.cst.functions.core,
  eu.esdihumboldt.cst.functions.core.join,
diff --git a/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Join.java b/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Join.java
index a84e48eb12..fda3195315 100644
--- a/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Join.java
+++ b/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Join.java
@@ -21,7 +21,10 @@
 import java.util.Collections;
 import java.util.List;
 
+import de.fhg.igd.slf4jplus.ALogger;
+import de.fhg.igd.slf4jplus.ALoggerFactory;
 import eu.esdihumboldt.cst.functions.core.join.IndexJoinHandler;
+import eu.esdihumboldt.cst.functions.core.join.JoinHandler;
 import eu.esdihumboldt.hale.common.align.model.Cell;
 import eu.esdihumboldt.hale.common.align.model.functions.JoinFunction;
 import eu.esdihumboldt.hale.common.align.model.functions.join.JoinParameter;
@@ -34,17 +37,38 @@
 /**
  * Type transformation that joins multiple instances of different source types
  * into one target instance, based on matching properties.
- * 
+ *
  * @author Kai Schwierczek
  */
 public class Join extends Retype implements JoinFunction, InstanceIndexContribution {
 
+	/**
+	 * The log
+	 */
+	private static final ALogger LOG = ALoggerFactory.getLogger(Join.class);
+
 	/**
 	 * @see eu.esdihumboldt.hale.common.align.transformation.function.impl.AbstractTypeTransformation#getInstanceHandler()
 	 */
 	@Override
 	public InstanceHandler<? super TransformationEngine> getInstanceHandler() {
-		return new IndexJoinHandler();
+		boolean useIndexJoinHandler = false;
+
+		String setting = System.getProperty("hale.functions.join.use_index_join_handler");
+
+		if (setting == null) {
+			setting = System.getenv("HALE_FUNCTIONS_USE_INDEX_JOIN_HANDLER");
+		}
+
+		if (setting != null) {
+			try {
+				useIndexJoinHandler = Boolean.valueOf(setting);
+			} catch (Throwable e) {
+				LOG.error("Error applying index join handler setting: " + setting, e);
+			}
+		}
+
+		return useIndexJoinHandler ? new IndexJoinHandler() : new JoinHandler();
 	}
 
 	/**
diff --git a/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Merge.java b/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Merge.java
index 6b13c54cd4..3f6c81386e 100644
--- a/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Merge.java
+++ b/cst/plugins/eu.esdihumboldt.cst.functions.core/src/eu/esdihumboldt/cst/functions/core/Merge.java
@@ -20,7 +20,10 @@
 import java.util.Collections;
 import java.util.List;
 
+import de.fhg.igd.slf4jplus.ALogger;
+import de.fhg.igd.slf4jplus.ALoggerFactory;
 import eu.esdihumboldt.cst.functions.core.merge.IndexMergeHandler;
+import eu.esdihumboldt.cst.functions.core.merge.PropertiesMergeHandler;
 import eu.esdihumboldt.hale.common.align.model.Cell;
 import eu.esdihumboldt.hale.common.align.model.functions.MergeFunction;
 import eu.esdihumboldt.hale.common.align.model.functions.merge.MergeUtil;
@@ -32,17 +35,38 @@
 /**
  * Type transformation that merges multiple instances of the same source type
  * into one target instance, based on matching properties.
- * 
+ *
  * @author Simon Templer
  */
 public class Merge extends Retype implements MergeFunction, InstanceIndexContribution {
 
+	/**
+	 * The log
+	 */
+	private static final ALogger LOG = ALoggerFactory.getLogger(Merge.class);
+
 	/**
 	 * @see eu.esdihumboldt.hale.common.align.transformation.function.impl.AbstractTypeTransformation#getInstanceHandler()
 	 */
 	@Override
 	public InstanceHandler<? super TransformationEngine> getInstanceHandler() {
-		return new IndexMergeHandler();
+		boolean useIndexMergeHandler = false;
+
+		String setting = System.getProperty("hale.functions.use_index_merge_handler");
+
+		if (setting == null) {
+			setting = System.getenv("HALE_FUNCTIONS_USE_INDEX_MERGE_HANDLER");
+		}
+
+		if (setting != null) {
+			try {
+				useIndexMergeHandler = Boolean.valueOf(setting);
+			} catch (Throwable e) {
+				LOG.error("Error applying index merge handler setting: " + setting, e);
+			}
+		}
+
+		return useIndexMergeHandler ? new IndexMergeHandler() : new PropertiesMergeHandler();
 	}
 
 	/**
diff --git a/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyJoin.java b/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyJoin.java
index fac74e7d4b..d208c6c568 100644
--- a/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyJoin.java
+++ b/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyJoin.java
@@ -18,8 +18,11 @@
 import java.util.Collection;
 import java.util.List;
 
+import de.fhg.igd.slf4jplus.ALogger;
+import de.fhg.igd.slf4jplus.ALoggerFactory;
 import eu.esdihumboldt.cst.functions.core.Join;
 import eu.esdihumboldt.cst.functions.core.join.IndexJoinHandler;
+import eu.esdihumboldt.cst.functions.core.join.JoinHandler;
 import eu.esdihumboldt.hale.common.align.model.Cell;
 import eu.esdihumboldt.hale.common.align.model.functions.JoinFunction;
 import eu.esdihumboldt.hale.common.align.model.impl.PropertyEntityDefinition;
@@ -32,11 +35,16 @@
  * into one target instance, based on matching properties. The transformation
  * also applies a Groovy script that can be used to control the target instance
  * creation.
- * 
+ *
  * @author Simon Templer
  */
 public class GroovyJoin extends GroovyRetype implements JoinFunction, InstanceIndexContribution {
 
+	/**
+	 * The log
+	 */
+	private static final ALogger LOG = ALoggerFactory.getLogger(GroovyJoin.class);
+
 	/**
 	 * The function ID. Not named <code>ID</code> to avoid shadowing
 	 * {@link JoinFunction#ID}.
@@ -50,7 +58,23 @@ public class GroovyJoin extends GroovyRetype implements JoinFunction, InstanceIn
 
 	@Override
 	public InstanceHandler<? super TransformationEngine> getInstanceHandler() {
-		return new IndexJoinHandler();
+		boolean useIndexJoinHandler = false;
+
+		String setting = System.getProperty("hale.functions.use_index_join_handler");
+
+		if (setting == null) {
+			setting = System.getenv("HALE_FUNCTIONS_USE_INDEX_JOIN_HANDLER");
+		}
+
+		if (setting != null) {
+			try {
+				useIndexJoinHandler = Boolean.valueOf(setting);
+			} catch (Throwable e) {
+				LOG.error("Error applying index join handler setting: " + setting, e);
+			}
+		}
+
+		return useIndexJoinHandler ? new IndexJoinHandler() : new JoinHandler();
 	}
 
 	/**
diff --git a/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyMerge.java b/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyMerge.java
index 892b66fff6..f6b0d9ef8c 100644
--- a/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyMerge.java
+++ b/cst/plugins/eu.esdihumboldt.cst.functions.groovy/src/eu/esdihumboldt/cst/functions/groovy/GroovyMerge.java
@@ -19,8 +19,11 @@
 import java.util.Collection;
 import java.util.List;
 
+import de.fhg.igd.slf4jplus.ALogger;
+import de.fhg.igd.slf4jplus.ALoggerFactory;
 import eu.esdihumboldt.cst.functions.core.Merge;
 import eu.esdihumboldt.cst.functions.core.merge.IndexMergeHandler;
+import eu.esdihumboldt.cst.functions.core.merge.PropertiesMergeHandler;
 import eu.esdihumboldt.hale.common.align.model.Cell;
 import eu.esdihumboldt.hale.common.align.model.functions.MergeFunction;
 import eu.esdihumboldt.hale.common.align.model.impl.PropertyEntityDefinition;
@@ -33,11 +36,16 @@
  * into one target instance, based on matching properties. The transformation
  * also applies a Groovy script that can be used to control the target instance
  * creation.
- * 
+ *
  * @author Simon Templer
  */
 public class GroovyMerge extends GroovyRetype implements MergeFunction, InstanceIndexContribution {
 
+	/**
+	 * The log
+	 */
+	private static final ALogger LOG = ALoggerFactory.getLogger(GroovyMerge.class);
+
 	/**
 	 * The function ID. Not named <code>ID</code> to avoid shadowing
 	 * {@link MergeFunction#ID}.
@@ -51,7 +59,23 @@ public class GroovyMerge extends GroovyRetype implements MergeFunction, Instance
 
 	@Override
 	public InstanceHandler<? super TransformationEngine> getInstanceHandler() {
-		return new IndexMergeHandler();
+		boolean useIndexMergeHandler = false;
+
+		String setting = System.getProperty("hale.functions.use_index_merge_handler");
+
+		if (setting == null) {
+			setting = System.getenv("HALE_FUNCTIONS_USE_INDEX_MERGE_HANDLER");
+		}
+
+		if (setting != null) {
+			try {
+				useIndexMergeHandler = Boolean.valueOf(setting);
+			} catch (Throwable e) {
+				LOG.error("Error applying index merge handler setting: " + setting, e);
+			}
+		}
+
+		return useIndexMergeHandler ? new IndexMergeHandler() : new PropertiesMergeHandler();
 	}
 
 	/**