diff --git a/xtraplatform-features-sql/src/main/java/de/ii/xtraplatform/features/sql/app/FeatureDecoderSql.java b/xtraplatform-features-sql/src/main/java/de/ii/xtraplatform/features/sql/app/FeatureDecoderSql.java
index f246e7a7d..e80a2a678 100644
--- a/xtraplatform-features-sql/src/main/java/de/ii/xtraplatform/features/sql/app/FeatureDecoderSql.java
+++ b/xtraplatform-features-sql/src/main/java/de/ii/xtraplatform/features/sql/app/FeatureDecoderSql.java
@@ -7,6 +7,7 @@
  */
 package de.ii.xtraplatform.features.sql.app;
 
+import com.google.common.collect.ImmutableSet;
 import de.ii.xtraplatform.features.domain.Decoder;
 import de.ii.xtraplatform.features.domain.DecoderFactory;
 import de.ii.xtraplatform.features.domain.FeatureEventHandler;
@@ -34,6 +35,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -46,7 +48,7 @@ public class FeatureDecoderSql
 
   private final Map<String, SchemaMapping> mappings;
   private final Query query;
-  private final List<List<String>> mainTablePaths;
+  private final Set<List<String>> mainTablePaths;
   private final FeatureStoreMultiplicityTracker multiplicityTracker;
   private final boolean isSingleFeature;
   private final Map<String, DecoderFactory> subDecoderFactories;
@@ -79,7 +81,9 @@ public FeatureDecoderSql(
     this.wkbDialect = wkbDialect;
 
     this.mainTablePaths =
-        sqlQueryMappings.stream().map(s -> s.getMainTable().getFullPath()).toList();
+        sqlQueryMappings.stream()
+            .map(s -> s.getMainTable().getFullPath())
+            .collect(ImmutableSet.toImmutableSet());
     List<List<String>> multiTables =
         sqlQueryMappings.stream()
             .flatMap(s -> s.getTables().stream())
diff --git a/xtraplatform-features/src/main/java/de/ii/xtraplatform/features/domain/NestingTracker.java b/xtraplatform-features/src/main/java/de/ii/xtraplatform/features/domain/NestingTracker.java
index 615d4bbfa..449062923 100644
--- a/xtraplatform-features/src/main/java/de/ii/xtraplatform/features/domain/NestingTracker.java
+++ b/xtraplatform-features/src/main/java/de/ii/xtraplatform/features/domain/NestingTracker.java
@@ -13,6 +13,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
+import java.util.Set;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -25,7 +26,9 @@ public class NestingTracker {
 
   private final FeatureEventHandler<?, ?, ModifiableContext<?, ?>> downstream;
   private final ModifiableContext<?, ?> context;
-  private final List<List<String>> mainPaths;
+  // a Set so the per-value isNotMain() membership test is O(1) instead of a linear scan of
+  // List<List<String>> with element-wise list equality
+  private final Set<List<String>> mainPaths;
   private final boolean flattenObjects;
   private final boolean flattenArrays;
   private final List<String> nestingStack;
@@ -36,7 +39,7 @@ public class NestingTracker {
   public <T extends ModifiableContext<?, ?>> NestingTracker(
       FeatureEventHandler<?, ?, T> downstream,
       T context,
-      List<List<String>> mainPaths,
+      Set<List<String>> mainPaths,
       boolean flattenObjects,
       boolean flattenArrays,
       boolean skippable) {