diff --git a/sources/src/main/java/net/minecraft/server/RegionFileCache.java b/sources/src/main/java/net/minecraft/server/RegionFileCache.java
index 2aea7f2ec..0c061fdd0 100644
--- a/sources/src/main/java/net/minecraft/server/RegionFileCache.java
+++ b/sources/src/main/java/net/minecraft/server/RegionFileCache.java
@@ -10,6 +10,10 @@ import java.util.Map;
 import com.destroystokyo.paper.PaperConfig; // Paper
 import java.util.LinkedHashMap; // Paper
 
+/**
+ * Akarin Changes Note
+ * 1) Removes unneed synchronization (performance)
+ */
 public class RegionFileCache {
 
     public static final Map<File, RegionFile> a = new LinkedHashMap(PaperConfig.regionFileCacheSize, 0.75f, true); // Spigot - private -> public, Paper - HashMap -> LinkedHashMap
@@ -94,7 +98,7 @@ public class RegionFileCache {
     }
 
     // CraftBukkit start - call sites hoisted for synchronization
-    public static /*synchronized*/ NBTTagCompound d(File file, int i, int j) throws IOException { // Akarin - remove synchronization // OBFHELPER: read
+    public static /*synchronized*/ NBTTagCompound d(File file, int i, int j) throws IOException { // Akarin - 1.13 backport - remove synchronization // OBFHELPER: read
         RegionFile regionfile = a(file, i, j);
 
         DataInputStream datainputstream = regionfile.a(i & 31, j & 31);
@@ -106,7 +110,7 @@ public class RegionFileCache {
         return NBTCompressedStreamTools.a(datainputstream);
     }
 
-    public static /*synchronized*/ void e(File file, int i, int j, NBTTagCompound nbttagcompound) throws IOException { // Akarin - remove synchronization // OBFHELPER: write
+    public static /*synchronized*/ void e(File file, int i, int j, NBTTagCompound nbttagcompound) throws IOException { // Akarin - 1.13 backport - remove synchronization // OBFHELPER: write
         RegionFile regionfile = a(file, i, j);
 
         DataOutputStream dataoutputstream = regionfile.b(i & 31, j & 31);
@@ -115,7 +119,7 @@ public class RegionFileCache {
     }
     // CraftBukkit end
 
-    public static /*synchronized*/ boolean chunkExists(File file, int i, int j) { // Akarin - remove synchronization
+    public static /*synchronized*/ boolean chunkExists(File file, int i, int j) { // Akarin - 1.13 backport - remove synchronization
         RegionFile regionfile = b(file, i, j);
 
         return regionfile != null ? regionfile.c(i & 31, j & 31) : false;
diff --git a/sources/src/main/java/net/minecraft/server/RegistryID.java b/sources/src/main/java/net/minecraft/server/RegistryID.java
index 61029bddc..89c490cec 100644
--- a/sources/src/main/java/net/minecraft/server/RegistryID.java
+++ b/sources/src/main/java/net/minecraft/server/RegistryID.java
@@ -5,6 +5,10 @@ import com.google.common.collect.Iterators;
 import java.util.Iterator;
 import javax.annotation.Nullable;
 
+/**
+ * Akarin Changes Note
+ * 1) BitSet for faster access (performance)
+ */
 public class RegistryID<K> implements Registry {
 
     private static final Object a = null;
@@ -13,12 +17,14 @@ public class RegistryID<K> implements Registry {
     private K[] d;
     private int e;
     private int f;
+    private java.util.BitSet usedIds; // Akarin - 1.13 backport
 
     public RegistryID(int i) {
         i = (int) ((float) i / 0.8F);
         this.b = (K[]) (new Object[i]);
         this.c = new int[i];
         this.d = (K[]) (new Object[i]);
+        this.usedIds = new java.util.BitSet(); // Akarin - 1.13 backport
     }
 
     public int getId(@Nullable K k0) {
@@ -42,9 +48,14 @@ public class RegistryID<K> implements Registry {
     }
 
     private int c() {
+        // Akarin start - 1.13 backport
+        /*
         while (this.e < this.d.length && this.d[this.e] != null) {
             ++this.e;
         }
+        */
+        this.e = this.usedIds.nextClearBit(0);
+        // Akarin end - 1.13 backport
 
         return this.e;
     }
@@ -58,6 +69,7 @@ public class RegistryID<K> implements Registry {
         this.d = (K[]) (new Object[i]);
         this.e = 0;
         this.f = 0;
+        this.usedIds.clear(); // Akarin - 1.13 backport
 
         for (int j = 0; j < aobject.length; ++j) {
             if (aobject[j] != null) {
@@ -83,6 +95,7 @@ public class RegistryID<K> implements Registry {
         this.b[k] = k0;
         this.c[k] = i;
         this.d[i] = k0;
+        this.usedIds.set(i); // Akarin - 1.13 backport
         ++this.f;
         if (i == this.e) {
             ++this.e;