diff --git a/pom.xml b/pom.xml
index 92caf13d0..5c6498a9e 100644
--- a/pom.xml
+++ b/pom.xml
@@ -465,5 +465,10 @@
             <version>4.1.73.Final</version>
             <scope>compile</scope>
         </dependency>
+        <dependency>
+            <groupId>it.unimi.dsi</groupId>
+            <artifactId>fastutil</artifactId>
+            <version>8.5.6</version>
+        </dependency>
     </dependencies>
 </project>
diff --git a/src/main/java/de/bixilon/minosoft/data/entities/meta/EntityData.kt b/src/main/java/de/bixilon/minosoft/data/entities/meta/EntityData.kt
index 4b7ee76a7..e2cac6da8 100644
--- a/src/main/java/de/bixilon/minosoft/data/entities/meta/EntityData.kt
+++ b/src/main/java/de/bixilon/minosoft/data/entities/meta/EntityData.kt
@@ -33,6 +33,7 @@ import de.bixilon.minosoft.util.logging.Log
 import de.bixilon.minosoft.util.logging.LogLevels
 import de.bixilon.minosoft.util.logging.LogMessageType
 import glm_.vec3.Vec3i
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
 import java.util.*
 
 class EntityData(
@@ -105,7 +106,7 @@ class EntityData(
         }
     }
 
-    inner class EntityDataHashMap : HashMap<Int, Any>() {
+    inner class EntityDataHashMap : Int2ObjectOpenHashMap<Any>() {
 
         operator fun <K> get(field: EntityDataFields): K {
             val index: Int = this@EntityData.connection.registries.getEntityMetaDataIndex(field) ?: return field.defaultValue.unsafeCast() // Can not find field.
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/BlockStateRegistry.kt b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/BlockStateRegistry.kt
index 2f201f36e..5ec70deb9 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/BlockStateRegistry.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/BlockStateRegistry.kt
@@ -15,10 +15,11 @@ package de.bixilon.minosoft.data.registries.registries.registry
 
 import de.bixilon.minosoft.data.registries.blocks.BlockState
 import de.bixilon.minosoft.protocol.protocol.ProtocolDefinition
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
 
 class BlockStateRegistry(var flattened: Boolean) : AbstractRegistry<BlockState?> {
     override var parent: AbstractRegistry<BlockState?>? = null
-    private val idMap: MutableMap<Int, BlockState> = mutableMapOf()
+    private val idMap: Int2ObjectOpenHashMap<BlockState> = Int2ObjectOpenHashMap()
 
     override val size: Int
         get() {
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/EnumRegistry.kt b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/EnumRegistry.kt
index 7c816ec82..86c5039c2 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/EnumRegistry.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/EnumRegistry.kt
@@ -17,6 +17,8 @@ import com.google.gson.JsonPrimitive
 import de.bixilon.kutil.cast.CastUtil.unsafeCast
 import de.bixilon.kutil.enums.ValuesEnum
 import de.bixilon.minosoft.util.collections.Clearable
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap
 import java.util.*
 
 class EnumRegistry<T : Enum<*>>(
@@ -26,8 +28,8 @@ class EnumRegistry<T : Enum<*>>(
 ) : Clearable, Parentable<EnumRegistry<T>> {
 
     private var initialized = false
-    private val idValueMap: MutableMap<Int, T> = mutableMapOf()
-    private val valueIdMap: MutableMap<T, Int> = mutableMapOf()
+    private val idValueMap: Int2ObjectOpenHashMap<T> = Int2ObjectOpenHashMap()
+    private val valueIdMap: Object2IntOpenHashMap<T> = Object2IntOpenHashMap()
 
     operator fun get(id: Int): T? {
         return idValueMap[id] ?: parent?.get(id)
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/FakeEnumRegistry.kt b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/FakeEnumRegistry.kt
index e292345a7..5926184e6 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/FakeEnumRegistry.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/FakeEnumRegistry.kt
@@ -17,13 +17,15 @@ import de.bixilon.kutil.json.JsonUtil.asJsonObject
 import de.bixilon.kutil.primitive.IntUtil.toInt
 import de.bixilon.minosoft.data.registries.registries.Registries
 import de.bixilon.minosoft.util.collections.Clearable
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap
 
 class FakeEnumRegistry<T : RegistryFakeEnumerable>(
     override var parent: FakeEnumRegistry<T>? = null,
 ) : Clearable, Parentable<FakeEnumRegistry<T>> {
     private var initialized = false
-    private val idValueMap: MutableMap<Int, T> = mutableMapOf()
-    private val valueIdMap: MutableMap<T, Int> = mutableMapOf()
+    private val idValueMap: Int2ObjectOpenHashMap<T> = Int2ObjectOpenHashMap()
+    private val valueIdMap: Object2IntOpenHashMap<T> = Object2IntOpenHashMap()
     private val nameValueMap: MutableMap<String, T> = mutableMapOf()
 
     operator fun get(name: String): T? {
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/Registry.kt b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/Registry.kt
index 9bb946651..a3d4e9350 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/Registry.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/Registry.kt
@@ -23,13 +23,15 @@ import de.bixilon.minosoft.data.registries.ResourceLocationAble
 import de.bixilon.minosoft.data.registries.registries.Registries
 import de.bixilon.minosoft.util.KUtil.toResourceLocation
 import de.bixilon.minosoft.util.json.ResourceLocationJsonMap.toResourceLocationMap
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap
 
 open class Registry<T : RegistryItem>(
     override var parent: AbstractRegistry<T>? = null,
 ) : AbstractRegistry<T> {
     private var initialized = false
-    protected val idValueMap: MutableMap<Int, T> = mutableMapOf()
-    protected val valueIdMap: MutableMap<T, Int> = mutableMapOf()
+    protected val idValueMap: Int2ObjectOpenHashMap<T> = Int2ObjectOpenHashMap()
+    protected val valueIdMap: Object2IntOpenHashMap<T> = Object2IntOpenHashMap()
     protected val resourceLocationMap: MutableMap<ResourceLocation, T> = mutableMapOf()
 
     override val size: Int
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/ResourceLocationRegistry.kt b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/ResourceLocationRegistry.kt
index 74eea707e..240aab3f2 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/ResourceLocationRegistry.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/registries/registry/ResourceLocationRegistry.kt
@@ -16,13 +16,15 @@ package de.bixilon.minosoft.data.registries.registries.registry
 import de.bixilon.kutil.primitive.IntUtil.toInt
 import de.bixilon.minosoft.data.registries.ResourceLocation
 import de.bixilon.minosoft.util.json.ResourceLocationJsonMap.toResourceLocationMap
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap
 
 class ResourceLocationRegistry(
     override var parent: AbstractRegistry<ResourceLocation>? = null,
 ) : AbstractRegistry<ResourceLocation> {
     private var initialized = false
-    private val idValueMap: MutableMap<Int, ResourceLocation> = mutableMapOf()
-    private val valueIdMap: MutableMap<ResourceLocation, Int> = mutableMapOf()
+    private val idValueMap: Int2ObjectOpenHashMap<ResourceLocation> = Int2ObjectOpenHashMap()
+    private val valueIdMap: Object2IntOpenHashMap<ResourceLocation> = Object2IntOpenHashMap()
 
 
     override val size: Int
diff --git a/src/main/java/de/bixilon/minosoft/data/registries/versions/Versions.kt b/src/main/java/de/bixilon/minosoft/data/registries/versions/Versions.kt
index fd16299a2..b7b55c4d5 100644
--- a/src/main/java/de/bixilon/minosoft/data/registries/versions/Versions.kt
+++ b/src/main/java/de/bixilon/minosoft/data/registries/versions/Versions.kt
@@ -28,12 +28,13 @@ import de.bixilon.minosoft.util.KUtil.toResourceLocation
 import de.bixilon.minosoft.util.logging.Log
 import de.bixilon.minosoft.util.logging.LogLevels
 import de.bixilon.minosoft.util.logging.LogMessageType
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
 
 object Versions : Iterable<Version> {
     private val VERSIONS_INDEX = "minosoft:mapping/versions.json".toResourceLocation()
     private val VERSIONS_BY_NAME: MutableMap<String, Version> = mutableMapOf()
-    private val VERSIONS_BY_ID: MutableMap<Int, Version> = mutableMapOf()
-    private val VERSIONS_BY_PROTOCOL: MutableMap<Int, Version> = mutableMapOf()
+    private val VERSIONS_BY_ID: Int2ObjectOpenHashMap<Version> = Int2ObjectOpenHashMap()
+    private val VERSIONS_BY_PROTOCOL: Int2ObjectOpenHashMap<Version> = Int2ObjectOpenHashMap()
     val AUTOMATIC = Version("Automatic", -1, -1, VersionTypes.RELEASE, mapOf(), mapOf())
 
     private fun addVersion(version: Version) {
diff --git a/src/main/java/de/bixilon/minosoft/data/world/WorldEntities.kt b/src/main/java/de/bixilon/minosoft/data/world/WorldEntities.kt
index 9b421686e..6b461a794 100644
--- a/src/main/java/de/bixilon/minosoft/data/world/WorldEntities.kt
+++ b/src/main/java/de/bixilon/minosoft/data/world/WorldEntities.kt
@@ -19,11 +19,13 @@ import de.bixilon.minosoft.data.abilities.Gamemodes
 import de.bixilon.minosoft.data.entities.entities.Entity
 import de.bixilon.minosoft.data.entities.entities.player.PlayerEntity
 import glm_.vec3.Vec3d
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap
 import java.util.*
 
 class WorldEntities : Iterable<Entity> {
-    private val idEntityMap: MutableMap<Int, Entity> = synchronizedMapOf()
-    private val entityIdMap: MutableMap<Entity, Int> = synchronizedMapOf()
+    private val idEntityMap: Int2ObjectOpenHashMap<Entity> = Int2ObjectOpenHashMap()
+    private val entityIdMap: Object2IntOpenHashMap<Entity> = Object2IntOpenHashMap()
     private val entityUUIDMap: MutableMap<Entity, UUID> = synchronizedMapOf()
     private val uuidEntityMap: MutableMap<UUID, Entity> = synchronizedMapOf()
 
diff --git a/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasElement.kt b/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasElement.kt
index fc0d319be..6d5ed3d61 100644
--- a/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasElement.kt
+++ b/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasElement.kt
@@ -16,12 +16,13 @@ package de.bixilon.minosoft.gui.rendering.gui.atlas
 import de.bixilon.minosoft.gui.rendering.system.base.texture.texture.AbstractTexture
 import glm_.vec2.Vec2
 import glm_.vec2.Vec2i
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
 
 class AtlasElement(
     override val texture: AbstractTexture,
     val start: Vec2i,
     val end: Vec2i,
-    val slots: Map<Int, Vec2iBinding>, // ToDo: Use an array?
+    val slots: Int2ObjectOpenHashMap<Vec2iBinding>, // ToDo: Use an array?
 ) : TextureLike {
     override val size: Vec2i = end - start
     override lateinit var uvStart: Vec2
diff --git a/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasManager.kt b/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasManager.kt
index 456d13366..1b8a6e324 100644
--- a/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasManager.kt
+++ b/src/main/java/de/bixilon/minosoft/gui/rendering/gui/atlas/AtlasManager.kt
@@ -23,6 +23,7 @@ import de.bixilon.minosoft.gui.rendering.util.vec.vec2.Vec2iUtil.toVec2i
 import de.bixilon.minosoft.util.KUtil.toResourceLocation
 import glm_.vec2.Vec2
 import glm_.vec2.Vec2i
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
 
 class AtlasManager(private val renderWindow: RenderWindow) {
     private lateinit var elements: Map<ResourceLocation, AtlasElement>
@@ -59,7 +60,7 @@ class AtlasManager(private val renderWindow: RenderWindow) {
             val texture = renderWindow.textureManager.staticTextures.createTexture(versionData["texture"].toResourceLocation(), mipmaps = false)
             val start = versionData["start"].toVec2i()
             val end = versionData["end"].toVec2i()
-            val slots: MutableMap<Int, Vec2iBinding> = mutableMapOf()
+            val slots: Int2ObjectOpenHashMap<Vec2iBinding> = Int2ObjectOpenHashMap()
 
             versionData["slots"].toJsonObject()?.let {
                 for ((slotId, slotData) in it) {
diff --git a/src/main/java/de/bixilon/minosoft/gui/rendering/gui/elements/items/ContainerItemsElement.kt b/src/main/java/de/bixilon/minosoft/gui/rendering/gui/elements/items/ContainerItemsElement.kt
index 3907cc0ad..9613cf7ca 100644
--- a/src/main/java/de/bixilon/minosoft/gui/rendering/gui/elements/items/ContainerItemsElement.kt
+++ b/src/main/java/de/bixilon/minosoft/gui/rendering/gui/elements/items/ContainerItemsElement.kt
@@ -22,11 +22,12 @@ import de.bixilon.minosoft.gui.rendering.gui.elements.Element
 import de.bixilon.minosoft.gui.rendering.gui.mesh.GUIVertexConsumer
 import de.bixilon.minosoft.gui.rendering.gui.mesh.GUIVertexOptions
 import glm_.vec2.Vec2i
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
 
 class ContainerItemsElement(
     guiRenderer: GUIRenderer,
     val container: Container,
-    val slots: Map<Int, Vec2iBinding>, // ToDo: Use an array?
+    val slots: Int2ObjectOpenHashMap<Vec2iBinding>, // ToDo: Use an array?
 ) : Element(guiRenderer) {
     private val itemElements: MutableMap<Int, ItemElementData> = synchronizedMapOf()
     private var revision = -1L
diff --git a/src/main/java/de/bixilon/minosoft/gui/rendering/world/WorldRenderer.kt b/src/main/java/de/bixilon/minosoft/gui/rendering/world/WorldRenderer.kt
index 735101ec3..695cd58ac 100644
--- a/src/main/java/de/bixilon/minosoft/gui/rendering/world/WorldRenderer.kt
+++ b/src/main/java/de/bixilon/minosoft/gui/rendering/world/WorldRenderer.kt
@@ -76,6 +76,8 @@ import de.bixilon.minosoft.util.chunk.ChunkUtil.received
 import glm_.vec2.Vec2i
 import glm_.vec3.Vec3
 import glm_.vec3.Vec3i
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.ints.IntOpenHashSet
 
 class WorldRenderer(
     private val connection: PlayConnection,
@@ -91,7 +93,7 @@ class WorldRenderer(
     private val fluidSectionPreparer: FluidSectionPreparer = FluidCullSectionPreparer(renderWindow)
     private val lightMap = LightMap(connection)
 
-    private val loadedMeshes: MutableMap<Vec2i, MutableMap<Int, WorldMesh>> = mutableMapOf() // all prepared (and up to date) meshes
+    private val loadedMeshes: MutableMap<Vec2i, Int2ObjectOpenHashMap<WorldMesh>> = mutableMapOf() // all prepared (and up to date) meshes
     private val loadedMeshesLock = ReadWriteLock()
 
     val maxPreparingTasks = maxOf(DefaultThreadPool.threadCount - 1, 1)
@@ -100,7 +102,7 @@ class WorldRenderer(
 
     private val queue: MutableList<WorldQueueItem> = synchronizedListOf() // queue, that is visible, and should be rendered
     private val queueLock = ReadWriteLock()
-    private val culledQueue: MutableMap<Vec2i, MutableSet<Int>> = mutableMapOf() // Chunk sections that can be prepared or have changed, but are not required to get rendered yet (i.e. culled chunks)
+    private val culledQueue: MutableMap<Vec2i, IntOpenHashSet> = mutableMapOf() // Chunk sections that can be prepared or have changed, but are not required to get rendered yet (i.e. culled chunks)
     private val culledQueueLock = ReadWriteLock()
 
     // ToDo: Sometimes if you clear the chunk cache a ton of times, the workers are maxed out and nothing happens anymore
@@ -189,7 +191,7 @@ class WorldRenderer(
             if (!chunk.isFullyLoaded) {
                 return@of
             }
-            val sectionHeights: MutableMap<Int, BooleanArray> = mutableMapOf()
+            val sectionHeights: Int2ObjectOpenHashMap<BooleanArray> = Int2ObjectOpenHashMap()
             for (blockPosition in it.blocks.keys) {
                 val neighbours = sectionHeights.getOrPut(blockPosition.sectionHeight) { BooleanArray(Directions.SIZE) }
                 val inSectionHeight = blockPosition.y.inSectionHeight
@@ -542,7 +544,7 @@ class WorldRenderer(
             return true
         } else {
             culledQueueLock.lock()
-            culledQueue.getOrPut(chunkPosition) { mutableSetOf() } += sectionHeight
+            culledQueue.getOrPut(chunkPosition) { IntOpenHashSet() } += sectionHeight
             culledQueueLock.unlock()
         }
         return false
@@ -606,7 +608,7 @@ class WorldRenderer(
             }
 
             loadedMeshesLock.lock()
-            val meshes = loadedMeshes.getOrPut(item.chunkPosition) { mutableMapOf() }
+            val meshes = loadedMeshes.getOrPut(item.chunkPosition) { Int2ObjectOpenHashMap() }
 
             meshes.put(item.sectionHeight, mesh)?.let {
                 this.visible.removeMesh(it)
@@ -719,18 +721,18 @@ class WorldRenderer(
         loadedMeshesLock.release()
 
         culledQueueLock.acquire()
-        val queue: MutableMap<Vec2i, MutableSet<Int>> = mutableMapOf() // The queue method needs the full lock of the culledQueue
+        val queue: MutableMap<Vec2i, IntOpenHashSet> = mutableMapOf() // The queue method needs the full lock of the culledQueue
         for ((chunkPosition, sectionHeights) in this.culledQueue) {
             if (!isChunkVisible(chunkPosition)) {
                 continue
             }
-            var chunkQueue: MutableSet<Int>? = null
+            var chunkQueue: IntOpenHashSet? = null
             for (sectionHeight in sectionHeights) {
                 if (!isSectionVisible(chunkPosition, sectionHeight, Vec3i.EMPTY, Vec3i(16), false)) {
                     continue
                 }
                 if (chunkQueue == null) {
-                    chunkQueue = queue.getOrPut(chunkPosition) { mutableSetOf() }
+                    chunkQueue = queue.getOrPut(chunkPosition) { IntOpenHashSet() }
                 }
                 chunkQueue += sectionHeight
             }
diff --git a/src/main/java/de/bixilon/minosoft/protocol/packets/s2c/play/entity/passenger/EntityPassengerS2CP.kt b/src/main/java/de/bixilon/minosoft/protocol/packets/s2c/play/entity/passenger/EntityPassengerS2CP.kt
index 1440e9142..846831fef 100644
--- a/src/main/java/de/bixilon/minosoft/protocol/packets/s2c/play/entity/passenger/EntityPassengerS2CP.kt
+++ b/src/main/java/de/bixilon/minosoft/protocol/packets/s2c/play/entity/passenger/EntityPassengerS2CP.kt
@@ -21,11 +21,12 @@ import de.bixilon.minosoft.util.KUtil.entities
 import de.bixilon.minosoft.util.logging.Log
 import de.bixilon.minosoft.util.logging.LogLevels
 import de.bixilon.minosoft.util.logging.LogMessageType
+import it.unimi.dsi.fastutil.ints.IntOpenHashSet
 
 @LoadPacket
 class EntityPassengerS2CP(buffer: PlayInByteBuffer) : PlayS2CPacket {
     val vehicleEntityId: Int = buffer.readVarInt()
-    val passengerEntityIds: Set<Int> = buffer.readVarIntArray().toSet()
+    val passengerEntityIds: IntOpenHashSet = IntOpenHashSet(buffer.readVarIntArray())
 
     override fun handle(connection: PlayConnection) {
         val vehicle = connection.world.entities[vehicleEntityId] ?: return
diff --git a/src/main/java/de/bixilon/minosoft/recipes/RecipeRegistry.kt b/src/main/java/de/bixilon/minosoft/recipes/RecipeRegistry.kt
index d8ffda2bf..384210bd8 100644
--- a/src/main/java/de/bixilon/minosoft/recipes/RecipeRegistry.kt
+++ b/src/main/java/de/bixilon/minosoft/recipes/RecipeRegistry.kt
@@ -17,12 +17,14 @@ import de.bixilon.minosoft.data.registries.ResourceLocation
 import de.bixilon.minosoft.data.registries.ResourceLocationAble
 import de.bixilon.minosoft.data.registries.registries.registry.AbstractRegistry
 import de.bixilon.minosoft.util.KUtil.toResourceLocation
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap
 
 class RecipeRegistry(
     override var parent: AbstractRegistry<Recipe>? = null,
 ) : AbstractRegistry<Recipe> {
-    private val idValueMap: MutableMap<Int, Recipe> = mutableMapOf()
-    private val valueIdMap: MutableMap<Recipe, Int> = mutableMapOf()
+    private val idValueMap: Int2ObjectOpenHashMap<Recipe> = Int2ObjectOpenHashMap()
+    private val valueIdMap: Object2IntOpenHashMap<Recipe> = Object2IntOpenHashMap()
     private val resourceLocationRecipeMap: MutableMap<ResourceLocation, Recipe> = mutableMapOf()
     private val recipeResourceLocationMap: MutableMap<Recipe, ResourceLocation> = mutableMapOf()