diff --git a/src/Snapshot.cs b/src/Snapshot.cs
index 4537e14..25f9bad 100644
--- a/src/Snapshot.cs
+++ b/src/Snapshot.cs
@@ -15,11 +15,11 @@ public class Snapshot : IDisposable
 
 	private List<RelationSnapshot> RelationSnapshots = new List<RelationSnapshot>();
 
-	private Dictionary<Entity, IndexableSet<TypeId>> EntityRelationIndex =
-		new Dictionary<Entity, IndexableSet<TypeId>>();
+	private List<IndexableSet<TypeId>> EntityRelationIndex =
+		new List<IndexableSet<TypeId>>();
 
-	private Dictionary<Entity, IndexableSet<TypeId>> EntityComponentIndex =
-		new Dictionary<Entity, IndexableSet<TypeId>>();
+	private List<IndexableSet<TypeId>> EntityComponentIndex =
+		new List<IndexableSet<TypeId>>();
 
 	private List<string> EntityTags = new List<string>();
 
@@ -76,32 +76,36 @@ public class Snapshot : IDisposable
 		// restore entity relation index state
 		// FIXME: arghhhh this is so slow
 
-		foreach (var (id, relationTypeSet) in world.EntityRelationIndex)
+		foreach (var relationTypeSet in world.EntityRelationIndex)
 		{
 			relationTypeSet.Clear();
 		}
 
-		foreach (var (id, relationTypeSet) in EntityRelationIndex)
+		for (var i = 0; i < EntityRelationIndex.Count; i += 1)
 		{
+			var relationTypeSet = EntityRelationIndex[i];
+
 			foreach (var typeId in relationTypeSet)
 			{
-				world.EntityRelationIndex[id].Add(typeId);
+				world.EntityRelationIndex[i].Add(typeId);
 			}
 		}
 
 		// restore entity component index state
 		// FIXME: arrghghhh this is so slow
 
-		foreach (var (id, componentTypeSet) in world.EntityComponentIndex)
+		foreach (var componentTypeSet in world.EntityComponentIndex)
 		{
 			componentTypeSet.Clear();
 		}
 
-		foreach (var (id, componentTypeSet) in EntityComponentIndex)
+		for (var i = 0; i < EntityComponentIndex.Count; i += 1)
 		{
+			var componentTypeSet = EntityComponentIndex[i];
+
 			foreach (var typeId in componentTypeSet)
 			{
-				world.EntityComponentIndex[id].Add(typeId);
+				world.EntityComponentIndex[i].Add(typeId);
 			}
 		}
 
@@ -145,37 +149,39 @@ public class Snapshot : IDisposable
 			RelationSnapshots[i].Take(world.RelationIndex[i]);
 		}
 
+		// fill in missing index structures
+
+		for (var i = EntityComponentIndex.Count; i < world.EntityComponentIndex.Count; i += 1)
+		{
+			EntityComponentIndex.Add(new IndexableSet<TypeId>());
+		}
+
+		for (var i = EntityRelationIndex.Count; i < world.EntityRelationIndex.Count; i += 1)
+		{
+			EntityRelationIndex.Add(new IndexableSet<TypeId>());
+		}
+
 		// copy entity relation index
 		// FIXME: arghhhh this is so slow
-		foreach (var (id, relationTypeSet) in world.EntityRelationIndex)
+		for (var i = 0; i < world.EntityRelationIndex.Count; i += 1)
 		{
-			if (!EntityRelationIndex.ContainsKey(id))
-			{
-				EntityRelationIndex.Add(id, new IndexableSet<TypeId>());
-			}
+			EntityRelationIndex[i].Clear();
 
-			EntityRelationIndex[id].Clear();
-
-			foreach (var typeId in relationTypeSet)
+			foreach (var typeId in world.EntityRelationIndex[i])
 			{
-				EntityRelationIndex[id].Add(typeId);
+				EntityRelationIndex[i].Add(typeId);
 			}
 		}
 
 		// copy entity component index
 		// FIXME: arghhhh this is so slow
-		foreach (var (id, componentTypeSet) in world.EntityComponentIndex)
+		for (var i = 0; i < world.EntityComponentIndex.Count; i += 1)
 		{
-			if (!EntityComponentIndex.ContainsKey(id))
-			{
-				EntityComponentIndex.Add(id, new IndexableSet<TypeId>());
-			}
+			EntityComponentIndex[i].Clear();
 
-			EntityComponentIndex[id].Clear();
-
-			foreach (var typeId in componentTypeSet)
+			foreach (var typeId in world.EntityComponentIndex[i])
 			{
-				EntityComponentIndex[id].Add(typeId);
+				EntityComponentIndex[i].Add(typeId);
 			}
 		}
 
@@ -346,12 +352,12 @@ public class Snapshot : IDisposable
 					relationSnapshot.Dispose();
 				}
 
-				foreach (var componentSet in EntityComponentIndex.Values)
+				foreach (var componentSet in EntityComponentIndex)
 				{
 					componentSet.Dispose();
 				}
 
-				foreach (var relationSet in EntityRelationIndex.Values)
+				foreach (var relationSet in EntityRelationIndex)
 				{
 					relationSet.Dispose();
 				}
diff --git a/src/World.cs b/src/World.cs
index 9ef9ff7..753d0b7 100644
--- a/src/World.cs
+++ b/src/World.cs
@@ -26,7 +26,7 @@ public class World : IDisposable
 
 	// Relation Storages
 	internal List<RelationStorage> RelationIndex = new List<RelationStorage>();
-	internal Dictionary<Entity, IndexableSet<TypeId>> EntityRelationIndex = new Dictionary<Entity, IndexableSet<TypeId>>();
+	internal List<IndexableSet<TypeId>> EntityRelationIndex = new List<IndexableSet<TypeId>>();
 
 	// Message Storages
 	private List<MessageStorage> MessageIndex = new List<MessageStorage>();
@@ -34,7 +34,7 @@ public class World : IDisposable
 	public FilterBuilder FilterBuilder => new FilterBuilder(this);
 
 	internal readonly List<ComponentStorage> ComponentIndex = new List<ComponentStorage>();
-	internal Dictionary<Entity, IndexableSet<TypeId>> EntityComponentIndex = new Dictionary<Entity, IndexableSet<TypeId>>();
+	internal List<IndexableSet<TypeId>> EntityComponentIndex = new List<IndexableSet<TypeId>>();
 
 	internal IdAssigner EntityIdAssigner = new IdAssigner();
 
@@ -97,10 +97,10 @@ public class World : IDisposable
 	{
 		var entity = new Entity(EntityIdAssigner.Assign());
 
-		if (!EntityComponentIndex.ContainsKey(entity))
+		if (entity.ID == EntityComponentIndex.Count)
 		{
-			EntityRelationIndex.Add(entity, new IndexableSet<TypeId>());
-			EntityComponentIndex.Add(entity, new IndexableSet<TypeId>());
+			EntityRelationIndex.Add(new IndexableSet<TypeId>());
+			EntityComponentIndex.Add(new IndexableSet<TypeId>());
 			EntityTags.Add(tag);
 		}
 
@@ -119,8 +119,11 @@ public class World : IDisposable
 
 	public void Destroy(in Entity entity)
 	{
+		var componentSet = EntityComponentIndex[(int) entity.ID];
+		var relationSet = EntityRelationIndex[(int) entity.ID];
+
 		// remove all components from storages
-		foreach (var componentTypeIndex in EntityComponentIndex[entity])
+		foreach (var componentTypeIndex in componentSet)
 		{
 			var componentStorage = ComponentIndex[componentTypeIndex];
 			componentStorage.Remove(entity);
@@ -132,14 +135,14 @@ public class World : IDisposable
 		}
 
 		// remove all relations from storage
-		foreach (var relationTypeIndex in EntityRelationIndex[entity])
+		foreach (var relationTypeIndex in relationSet)
 		{
 			var relationStorage = RelationIndex[relationTypeIndex];
 			relationStorage.RemoveEntity(entity);
 		}
 
-		EntityComponentIndex[entity].Clear();
-		EntityRelationIndex[entity].Clear();
+		componentSet.Clear();
+		relationSet.Clear();
 
 		// recycle ID
 		EntityIdAssigner.Unassign(entity.ID);
@@ -155,7 +158,7 @@ public class World : IDisposable
 
 	internal bool Has(in Entity entity, in TypeId typeId)
 	{
-		return EntityComponentIndex[entity].Contains(typeId);
+		return EntityComponentIndex[(int) entity.ID].Contains(typeId);
 	}
 
 	public bool Some<T>() where T : unmanaged
@@ -188,7 +191,7 @@ public class World : IDisposable
 
 		if (!componentStorage.Set(entity, component))
 		{
-			EntityComponentIndex[entity].Add(componentStorage.TypeId);
+			EntityComponentIndex[(int) entity.ID].Add(componentStorage.TypeId);
 
 			foreach (var filter in ComponentTypeToFilter[componentStorage.TypeId])
 			{
@@ -203,7 +206,7 @@ public class World : IDisposable
 
 		if (componentStorage.Remove(entity))
 		{
-			EntityComponentIndex[entity].Remove(componentStorage.TypeId);
+			EntityComponentIndex[(int) entity.ID].Remove(componentStorage.TypeId);
 
 			foreach (var filter in ComponentTypeToFilter[componentStorage.TypeId])
 			{
@@ -235,8 +238,8 @@ public class World : IDisposable
 	{
 		var relationStorage = GetRelationStorage<T>();
 		relationStorage.Set(entityA, entityB, relation);
-		EntityRelationIndex[entityA].Add(new TypeId(RelationTypeIdAssigner<T>.Id));
-		EntityRelationIndex[entityB].Add(new TypeId(RelationTypeIdAssigner<T>.Id));
+		EntityRelationIndex[(int) entityA.ID].Add(new TypeId(RelationTypeIdAssigner<T>.Id));
+		EntityRelationIndex[(int) entityB.ID].Add(new TypeId(RelationTypeIdAssigner<T>.Id));
 	}
 
 	public void Unrelate<T>(in Entity entityA, in Entity entityB) where T : unmanaged
@@ -388,7 +391,7 @@ public class World : IDisposable
 #if DEBUG
 	public ComponentTypeEnumerator Debug_GetAllComponentTypes(Entity entity)
 	{
-		return new ComponentTypeEnumerator(this, EntityComponentIndex[entity]);
+		return new ComponentTypeEnumerator(this, EntityComponentIndex[(int) entity.ID]);
 	}
 
 	public IEnumerable<Entity> Debug_GetEntities(Type componentType)
@@ -457,14 +460,14 @@ public class World : IDisposable
 					messageStorage.Dispose();
 				}
 
-				foreach (var typeSet in EntityComponentIndex.Values)
+				foreach (var componentSet in EntityComponentIndex)
 				{
-					typeSet.Dispose();
+					componentSet.Dispose();
 				}
 
-				foreach (var typeSet in EntityRelationIndex.Values)
+				foreach (var relationSet in EntityRelationIndex)
 				{
-					typeSet.Dispose();
+					relationSet.Dispose();
 				}
 
 				foreach (var filter in FilterIndex.Values)