From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sat, 11 Apr 2020 03:56:07 -0400
Subject: [PATCH] Implement Chunk Priority / Urgency System for Chunks

Mark chunks that are blocking main thread for world generation as urgent

Implements a general priority system so that chunks that are sorted in
the generator queues can prioritize certain chunks over another.

Urgent chunks will jump to the front of the line, ensuring that a
sync chunk load on an ungenerated chunk does not lag the server for
a long period of time if the servers generator queues are filled with
lots of chunks already.

This massively reduces the lag spikes from sync chunk gens.

Then we further prioritize loading order so nearby chunks have higher
priority than distant chunks, reducing the pressure a high no tick
view distance holds on you.

Chunks in front of the player have higher priority, to help with
fast traveling players keep up with their movement.

1.17 update note: very big diff skipping for now, still needs to be updated

diff --git a/src/main/java/com/destroystokyo/paper/io/chunk/ChunkTaskManager.java b/src/main/java/com/destroystokyo/paper/io/chunk/ChunkTaskManager.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/com/destroystokyo/paper/io/chunk/ChunkTaskManager.java
+++ b/src/main/java/com/destroystokyo/paper/io/chunk/ChunkTaskManager.java
@@ -0,0 +0,0 @@ public final class ChunkTaskManager {
     }
 
     static void dumpChunkInfo(Set<ChunkHolder> seenChunks, ChunkHolder chunkHolder, int x, int z) {
-        dumpChunkInfo(seenChunks, chunkHolder, x, z, 0, 1);
+        dumpChunkInfo(seenChunks, chunkHolder, x, z, 0, 4);
     }
 
     static void dumpChunkInfo(Set<ChunkHolder> seenChunks, ChunkHolder chunkHolder, int x, int z, int indent, int maxDepth) {
@@ -0,0 +0,0 @@ public final class ChunkTaskManager {
             PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "Chunk Status - " + ((chunk == null) ? "null chunk" : chunk.getStatus().toString()));
             PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "Chunk Ticket Status - "  + ChunkHolder.getStatus(chunkHolder.getTicketLevel()));
             PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "Chunk Holder Status - " + ((holderStatus == null) ? "null" : holderStatus.toString()));
+            PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "Chunk Holder Priority - " + chunkHolder.getQueueLevel());
+
+            if (!chunkHolder.neighbors.isEmpty()) {
+                if (indent >= maxDepth) {
+                    PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "Chunk Neighbors: (Can't show, too deeply nested)");
+                    return;
+                }
+                PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "Chunk Neighbors: ");
+                for (ChunkHolder neighbor : chunkHolder.neighbors.keySet()) {
+                    ChunkStatus status = neighbor.getChunkHolderStatus();
+                    if (status != null && status.isOrAfter(ChunkHolder.getStatus(neighbor.getTicketLevel()))) {
+                        continue;
+                    }
+                    int nx = neighbor.pos.x;
+                    int nz = neighbor.pos.z;
+                    if (seenChunks.contains(neighbor)) {
+                        PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "  " + nx + "," + nz + " in " + chunkHolder.getWorld().getWorld().getName() + " (CIRCULAR)");
+                        continue;
+                    }
+                    PaperFileIOThread.LOGGER.log(Level.ERROR, indentStr + "  " + nx + "," + nz + " in " + chunkHolder.getWorld().getWorld().getName() + ":");
+                    dumpChunkInfo(seenChunks, neighbor, nx, nz, indent + 1, maxDepth);
+                }
+            }
+
         }
     }
 
diff --git a/src/main/java/net/minecraft/server/level/ChunkHolder.java b/src/main/java/net/minecraft/server/level/ChunkHolder.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ChunkHolder.java
+++ b/src/main/java/net/minecraft/server/level/ChunkHolder.java
@@ -0,0 +0,0 @@
 package net.minecraft.server.level;
 
+import com.destroystokyo.paper.io.PrioritizedTaskQueue;
 import com.mojang.datafixers.util.Either;
 import it.unimi.dsi.fastutil.shorts.ShortArraySet;
 import it.unimi.dsi.fastutil.shorts.ShortSet;
@@ -0,0 +0,0 @@ public class ChunkHolder {
     private final DebugBuffer<ChunkHolder.ChunkSaveDebug> chunkToSaveHistory;
     public int oldTicketLevel;
     private int ticketLevel;
-    private int queueLevel;
+    volatile int queueLevel; // Paper - make volatile since this is concurrently accessed
     public final ChunkPos pos; // Paper - package->public
     private boolean hasChangedSections;
     private final ShortSet[] changedBlocksPerSection;
@@ -0,0 +0,0 @@ public class ChunkHolder {
 
     boolean isUpdateQueued = false; // Paper
     private final ChunkMap chunkMap; // Paper
+    public ServerLevel getWorld() { return chunkMap.level; } // Paper
     // Paper start - no-tick view distance
     public final LevelChunk getSendingChunk() {
         // it's important that we use getChunkAtIfLoadedImmediately to mirror the chunk sending logic used
@@ -0,0 +0,0 @@ public class ChunkHolder {
     // Paper end - optimise isOutsideOfRange
     long lastAutoSaveTime; // Paper - incremental autosave
     long inactiveTimeStart; // Paper - incremental autosave
+    // Paper start - Chunk gen/load priority system
+    volatile int neighborPriority = -1;
+    volatile int priorityBoost = 0;
+    public final java.util.concurrent.ConcurrentHashMap<ChunkHolder, ChunkStatus> neighbors = new java.util.concurrent.ConcurrentHashMap<>();
+    public final it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap<Integer> neighborPriorities = new it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap<>();
+
+    private int getDemandedPriority() {
+        int priority = neighborPriority; // if we have a neighbor priority, use it
+        int myPriority = getMyPriority();
+
+        if (priority == -1 || (ticketLevel <= 33 && priority > myPriority)) {
+            priority = myPriority;
+        }
+
+        return Math.max(1, Math.min(Math.max(ticketLevel, ChunkMap.MAX_CHUNK_DISTANCE), priority));
+    }
+
+    private int getMyPriority() {
+        if (priorityBoost == DistanceManager.URGENT_PRIORITY) {
+            return 2; // Urgent - ticket level isn't always 31 so 33-30 = 3, but allow 1 more tasks to go below this for dependents
+        }
+        return ticketLevel - priorityBoost;
+    }
+
+    private int getNeighborsPriority() {
+        return (neighborPriorities.isEmpty() ? getMyPriority() : getDemandedPriority()) + 1;
+    }
+
+    public void onNeighborRequest(ChunkHolder neighbor, ChunkStatus status) {
+        neighbor.setNeighborPriority(this, getNeighborsPriority());
+        this.neighbors.compute(neighbor, (playerChunk, currentWantedStatus) -> {
+            if (currentWantedStatus == null || !currentWantedStatus.isOrAfter(status)) {
+                //System.out.println(this + " request " + neighbor + " at " + status + " currently " + currentWantedStatus);
+                return status;
+            } else {
+                //System.out.println(this + " requested " + neighbor + " at " + status + " but thats lower than other wanted status " + currentWantedStatus);
+                return currentWantedStatus;
+            }
+        });
+
+    }
+
+    public void onNeighborDone(ChunkHolder neighbor, ChunkStatus chunkstatus, ChunkAccess chunk) {
+        this.neighbors.compute(neighbor, (playerChunk, wantedStatus) -> {
+            if (wantedStatus != null && chunkstatus.isOrAfter(wantedStatus)) {
+                //System.out.println(this + " neighbor done at " + neighbor + " for status " + chunkstatus + " wanted " + wantedStatus);
+                neighbor.removeNeighborPriority(this);
+                return null;
+            } else {
+                //System.out.println(this + " neighbor finished our previous request at " + neighbor + " for status " + chunkstatus + " but we now want instead " + wantedStatus);
+                return wantedStatus;
+            }
+        });
+    }
+
+    private void removeNeighborPriority(ChunkHolder requester) {
+        synchronized (neighborPriorities) {
+            neighborPriorities.remove(requester.pos.toLong());
+            recalcNeighborPriority();
+        }
+        checkPriority();
+    }
+
+
+    private void setNeighborPriority(ChunkHolder requester, int priority) {
+        synchronized (neighborPriorities) {
+            neighborPriorities.put(requester.pos.toLong(), Integer.valueOf(priority));
+            recalcNeighborPriority();
+        }
+        checkPriority();
+    }
 
+    private void recalcNeighborPriority() {
+        neighborPriority = -1;
+        if (!neighborPriorities.isEmpty()) {
+            synchronized (neighborPriorities) {
+                for (Integer neighbor : neighborPriorities.values()) {
+                    if (neighbor < neighborPriority || neighborPriority == -1) {
+                        neighborPriority = neighbor;
+                    }
+                }
+            }
+        }
+    }
+    private void checkPriority() {
+        if (getQueueLevel() != getDemandedPriority()) this.chunkMap.queueHolderUpdate(this);
+    }
+
+    public final double getDistance(ServerPlayer player) {
+        return getDistance(player.getX(), player.getZ());
+    }
+    public final double getDistance(double blockX, double blockZ) {
+        int cx = net.minecraft.server.MCUtil.fastFloor(blockX) >> 4;
+        int cz = net.minecraft.server.MCUtil.fastFloor(blockZ) >> 4;
+        final double x = pos.x - cx;
+        final double z = pos.z - cz;
+        return (x * x) + (z * z);
+    }
+
+    public final double getDistanceFrom(BlockPos pos) {
+        return getDistance(pos.getX(), pos.getZ());
+    }
+
+    @Override
+    public String toString() {
+        return "PlayerChunk{" +
+            "location=" + pos +
+            ", ticketLevel=" + ticketLevel + "/" + getStatus(this.ticketLevel) +
+            ", chunkHolderStatus=" + getChunkHolderStatus() +
+            ", neighborPriority=" + getNeighborsPriority() +
+            ", priority=(" + ticketLevel + " - " + priorityBoost +" vs N " + neighborPriority + ") = " + getDemandedPriority() + " A " + getQueueLevel() +
+            '}';
+    }
+    // Paper end
     public ChunkHolder(ChunkPos pos, int level, LevelHeightAccessor world, LevelLightEngine lightingProvider, ChunkHolder.LevelChangeListener levelUpdateListener, ChunkHolder.PlayerProvider playersWatchingChunkProvider) {
         this.futures = new AtomicReferenceArray(ChunkHolder.CHUNK_STATUSES.size());
         this.fullChunkFuture = ChunkHolder.UNLOADED_LEVEL_CHUNK_FUTURE;
@@ -0,0 +0,0 @@ public class ChunkHolder {
         return null;
     }
     // CraftBukkit end
-
+    public static ChunkStatus getNextStatus(ChunkStatus status) {
+        if (status == ChunkStatus.FULL) {
+               return status;
+            }
+        return CHUNK_STATUSES.get(status.getIndex() + 1);
+    }
+    public CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> getStatusFutureUncheckedMain(ChunkStatus chunkstatus) {
+            return ensureMain(getFutureIfPresentUnchecked(chunkstatus));
+        }
+    public <T> CompletableFuture<T> ensureMain(CompletableFuture<T> future) {
+        return future.thenApplyAsync(r -> r, chunkMap.mainInvokingExecutor);
+    }
     public CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> getFutureIfPresentUnchecked(ChunkStatus leastStatus) {
         CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> completablefuture = (CompletableFuture) this.futures.get(leastStatus.getIndex());
 
@@ -0,0 +0,0 @@ public class ChunkHolder {
         // CraftBukkit start
         // ChunkUnloadEvent: Called before the chunk is unloaded: isChunkLoaded is still true and chunk can still be modified by plugins.
         if (playerchunk_state.isOrAfter(ChunkHolder.FullChunkStatus.BORDER) && !playerchunk_state1.isOrAfter(ChunkHolder.FullChunkStatus.BORDER)) {
-            this.getFutureIfPresentUnchecked(ChunkStatus.FULL).thenAccept((either) -> {
+            this.getStatusFutureUncheckedMain(ChunkStatus.FULL).thenAccept((either) -> { // Paper - ensure main
                 LevelChunk chunk = (LevelChunk)either.left().orElse(null);
                 if (chunk != null) {
                     chunkStorage.callbackExecutor.execute(() -> {
@@ -0,0 +0,0 @@ public class ChunkHolder {
             this.fullChunkFuture = chunkStorage.prepareAccessibleChunk(this);
             this.scheduleFullChunkPromotion(chunkStorage, this.fullChunkFuture, executor, ChunkHolder.FullChunkStatus.BORDER);
             // Paper start - cache ticking ready status
-            this.fullChunkFuture.thenAccept(either -> {
+            ensureMain(this.fullChunkFuture).thenAccept(either -> { // Paper ensureMain
                 final Optional<LevelChunk> left = either.left();
                 if (left.isPresent() && ChunkHolder.this.fullChunkCreateCount == expectCreateCount) {
                     // note: Here is a very good place to add callbacks to logic waiting on this.
                     LevelChunk fullChunk = either.left().get();
                     ChunkHolder.this.isFullChunkReady = true;
                     fullChunk.playerChunk = ChunkHolder.this;
+                    this.chunkMap.getDistanceManager().clearPriorityTickets(pos);
                 }
             });
             this.updateChunkToSave(this.fullChunkFuture, "full");
@@ -0,0 +0,0 @@ public class ChunkHolder {
             this.tickingChunkFuture = chunkStorage.prepareTickingChunk(this);
             this.scheduleFullChunkPromotion(chunkStorage, this.tickingChunkFuture, executor, ChunkHolder.FullChunkStatus.TICKING);
             // Paper start - cache ticking ready status
-            this.tickingChunkFuture.thenAccept(either -> {
+            ensureMain(this.tickingChunkFuture).thenAccept(either -> {// Paper - ensureMain
                 either.ifLeft(chunk -> {
                     // note: Here is a very good place to add callbacks to logic waiting on this.
-                    ChunkHolder.this.isTickingReady = true;
-
+                    LevelChunk fullChunk = either.left().get();
+                    ChunkHolder.this.isFullChunkReady = true;
+                    fullChunk.playerChunk = ChunkHolder.this;
                     // Paper start - rewrite ticklistserver
                     ChunkHolder.this.chunkMap.level.onChunkSetTicking(ChunkHolder.this.pos.x, ChunkHolder.this.pos.z);
                     // Paper end - rewrite ticklistserver
@@ -0,0 +0,0 @@ public class ChunkHolder {
             this.entityTickingChunkFuture = chunkStorage.prepareEntityTickingChunk(this.pos);
             this.scheduleFullChunkPromotion(chunkStorage, this.entityTickingChunkFuture, executor, ChunkHolder.FullChunkStatus.ENTITY_TICKING);
             // Paper start - cache ticking ready status
-            this.entityTickingChunkFuture.thenAccept(either -> {
+            ensureMain(this.entityTickingChunkFuture).thenAccept(either -> {// Paper - ensureMain
                 either.ifLeft(chunk -> {
                     ChunkHolder.this.isEntityTickingReady = true;
                 });
@@ -0,0 +0,0 @@ public class ChunkHolder {
         }
 
         this.onLevelChange.onLevelChange(this.pos, this::getQueueLevel, this.ticketLevel, this::setQueueLevel);
+        // Paper start - raise IO/load priority if priority changes, use our preferred priority
+        priorityBoost = this.chunkMap.getDistanceManager().getChunkPriority(pos);
+        int priority = getDemandedPriority();
+        if (getQueueLevel() > priority) {
+            int ioPriority = PrioritizedTaskQueue.NORMAL_PRIORITY;
+            if (priority <= 10) {
+                ioPriority = PrioritizedTaskQueue.HIGHEST_PRIORITY;
+            } else if (priority <= 20) {
+                ioPriority = PrioritizedTaskQueue.HIGH_PRIORITY;
+            }
+            chunkMap.level.asyncChunkTaskManager.raisePriority(pos.x, pos.z, ioPriority);
+        }
+        if (getQueueLevel() != priority) {
+            this.onLevelChange.onLevelChange(this.pos, this::getQueueLevel, priority, this::setQueueLevel); // use preferred priority
+            int neighborsPriority = getNeighborsPriority();
+            this.neighbors.forEach((neighbor, neighborDesired) -> neighbor.setNeighborPriority(this, neighborsPriority));
+        }
+        // Paper end
         this.oldTicketLevel = this.ticketLevel;
         // CraftBukkit start
         // ChunkLoadEvent: Called after the chunk is loaded: isChunkLoaded returns true and chunk is ready to be modified by plugins.
         if (!playerchunk_state.isOrAfter(ChunkHolder.FullChunkStatus.BORDER) && playerchunk_state1.isOrAfter(ChunkHolder.FullChunkStatus.BORDER)) {
-            this.getFutureIfPresentUnchecked(ChunkStatus.FULL).thenAccept((either) -> {
+            this.getStatusFutureUncheckedMain(ChunkStatus.FULL).thenAccept((either) -> {// Paper - ensure main
                 LevelChunk chunk = (LevelChunk)either.left().orElse(null);
                 if (chunk != null) {
                     chunkStorage.callbackExecutor.execute(() -> {
@@ -0,0 +0,0 @@ public class ChunkHolder {
     @FunctionalInterface
     public interface LevelChangeListener {
 
+        default void changePriority(ChunkPos chunkcoordintpair, IntSupplier intsupplier, int i, IntConsumer intconsumer) { onLevelChange(chunkcoordintpair, intsupplier, i, intconsumer); } // Paper - OBFHELPER
         void onLevelChange(ChunkPos pos, IntSupplier levelGetter, int targetLevel, IntConsumer levelSetter);
     }
 
diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     public final ServerLevel level;
     private final ThreadedLevelLightEngine lightEngine;
     private final BlockableEventLoop<Runnable> mainThreadExecutor;
+    final java.util.concurrent.Executor mainInvokingExecutor; // Paper
     public final ChunkGenerator generator;
     private final Supplier<DimensionDataStorage> overworldDataStorage; public final Supplier<DimensionDataStorage> getWorldPersistentDataSupplier() { return this.overworldDataStorage; } // Paper - OBFHELPER
     private final PoiManager poiManager;
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
         @Override
         public void execute(Runnable runnable) {
+            org.spigotmc.AsyncCatcher.catchOp("Callback Executor execute"); // Paper
             if (this.queue == null) {
                 this.queue = new java.util.ArrayDeque<>();
             }
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
         @Override
         public void run() {
+            org.spigotmc.AsyncCatcher.catchOp("Callback Executor run"); // Paper
             if (this.queue == null) {
                 return;
             }
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         this.level = world;
         this.generator = chunkGenerator;
         this.mainThreadExecutor = mainThreadExecutor;
+        // Paper start
+        this.mainInvokingExecutor = (run) -> {
+            if (MCUtil.isMainThread()) {
+                run.run();
+            } else {
+                mainThreadExecutor.execute(run);
+            }
+        };
+        // Paper end
         ProcessorMailbox<Runnable> threadedmailbox = ProcessorMailbox.create(executor, "worldgen");
 
         Objects.requireNonNull(mainThreadExecutor);
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         this.playerViewDistanceTickMap = new com.destroystokyo.paper.util.misc.PlayerAreaMap(this.pooledLinkedPlayerHashSets,
             (ServerPlayer player, int rangeX, int rangeZ, int currPosX, int currPosZ, int prevPosX, int prevPosZ,
              com.destroystokyo.paper.util.misc.PooledLinkedHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> newState) -> {
+                checkHighPriorityChunks(player);
                 if (newState.size() != 1) {
                     return;
                 }
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                 }
                 ChunkPos chunkPos = new ChunkPos(rangeX, rangeZ);
                 ChunkMap.this.level.getChunkSource().removeTicketAtLevel(TicketType.PLAYER, chunkPos, 31, chunkPos); // entity ticking level, TODO check on update
-            });
+                ChunkMap.this.level.getChunkSource().clearPriorityTickets(chunkPos);
+            }, (player, prevPos, newPos) -> {
+            player.lastHighPriorityChecked = -1; // reset and recheck
+            checkHighPriorityChunks(player);
+        });
         this.playerViewDistanceNoTickMap = new com.destroystokyo.paper.util.misc.PlayerAreaMap(this.pooledLinkedPlayerHashSets);
         this.playerViewDistanceBroadcastMap = new com.destroystokyo.paper.util.misc.PlayerAreaMap(this.pooledLinkedPlayerHashSets,
             (ServerPlayer player, int rangeX, int rangeZ, int currPosX, int currPosZ, int prevPosX, int prevPosZ,
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
             });
         // Paper end - no-tick view distance
     }
+    // Paper start - Chunk Prioritization
+    public void queueHolderUpdate(ChunkHolder playerchunk) {
+        Runnable runnable = () -> {
+            if (isUnloading(playerchunk)) {
+                return; // unloaded
+            }
+            distanceManager.pendingChunkUpdates.add(playerchunk);
+            if (!distanceManager.pollingPendingChunkUpdates) {
+                level.getChunkSource().runDistanceManagerUpdates();
+            }
+        };
+        if (MCUtil.isMainThread()) {
+            // We can't use executor here because it will not execute tasks if its currently in the middle of executing tasks...
+            runnable.run();
+        } else {
+            mainThreadExecutor.execute(runnable);
+        }
+    }
 
     // Paper start
+    private boolean isUnloading(ChunkHolder playerchunk) {
+        return playerchunk == null || toDrop.contains(playerchunk.pos.toLong());
+    }
+
+    private void updateChunkPriorityMap(it.unimi.dsi.fastutil.longs.Long2IntOpenHashMap map, long chunk, int level) {
+        int prev = map.getOrDefault(chunk, -1);
+        if (level > prev) {
+            map.put(chunk, level);
+        }
+    }
+
+    public void checkHighPriorityChunks(ServerPlayer player) {
+        int currentTick = MinecraftServer.currentTick;
+        if (currentTick - player.lastHighPriorityChecked < 20 || !player.isRealPlayer) { // weed out fake players
+            return;
+        }
+        player.lastHighPriorityChecked = currentTick;
+        it.unimi.dsi.fastutil.longs.Long2IntOpenHashMap priorities = new it.unimi.dsi.fastutil.longs.Long2IntOpenHashMap();
+
+        int viewDistance = getEffectiveNoTickViewDistance();
+        net.minecraft.core.BlockPos.MutableBlockPos pos = new net.minecraft.core.BlockPos.MutableBlockPos();
+
+        // Prioritize circular near
+        double playerChunkX = Mth.floor(player.getX()) >> 4;
+        double playerChunkZ = Mth.floor(player.getZ()) >> 4;
+        pos.setValues(player.getX(), 0, player.getZ());
+        double twoThirdModifier = 2D / 3D;
+        MCUtil.getSpiralOutChunks(pos, Math.min(6, viewDistance)).forEach(coord -> {
+            if (shouldSkipPrioritization(coord)) return;
+
+            double dist = MCUtil.distance(playerChunkX, 0, playerChunkZ, coord.x, 0, coord.z);
+            // Prioritize immediate
+            if (dist <= 4) {
+                updateChunkPriorityMap(priorities, coord.toLong(), (int) (27 - dist));
+                return;
+            }
+
+            // Prioritize nearby chunks
+            updateChunkPriorityMap(priorities, coord.toLong(), (int) (20 - dist * twoThirdModifier));
+        });
+
+        // Prioritize Frustum near 3
+        ChunkPos front3 = player.getChunkInFront(3);
+        pos.setValues(front3.x << 4, 0, front3.z << 4);
+        MCUtil.getSpiralOutChunks(pos, Math.min(5, viewDistance)).forEach(coord -> {
+            if (shouldSkipPrioritization(coord)) return;
+
+            double dist = MCUtil.distance(playerChunkX, 0, playerChunkZ, coord.x, 0, coord.z);
+            updateChunkPriorityMap(priorities, coord.toLong(), (int) (25 - dist * twoThirdModifier));
+        });
+
+        // Prioritize Frustum near 5
+        if (viewDistance > 4) {
+            ChunkPos front5 = player.getChunkInFront(5);
+            pos.setValues(front5.x << 4, 0, front5.z << 4);
+            MCUtil.getSpiralOutChunks(pos, 4).forEach(coord -> {
+                if (shouldSkipPrioritization(coord)) return;
+
+                double dist = MCUtil.distance(playerChunkX, 0, playerChunkZ, coord.x, 0, coord.z);
+                updateChunkPriorityMap(priorities, coord.toLong(), (int) (25 - dist * twoThirdModifier));
+            });
+        }
+
+        // Prioritize Frustum far 7
+        if (viewDistance > 6) {
+            ChunkPos front7 = player.getChunkInFront(7);
+            pos.setValues(front7.x << 4, 0, front7.z << 4);
+            MCUtil.getSpiralOutChunks(pos, 3).forEach(coord -> {
+                if (shouldSkipPrioritization(coord)) {
+                    return;
+                }
+                double dist = MCUtil.distance(playerChunkX, 0, playerChunkZ, coord.x, 0, coord.z);
+                updateChunkPriorityMap(priorities, coord.toLong(), (int) (25 - dist * twoThirdModifier));
+            });
+        }
+
+        if (priorities.isEmpty()) return;
+        distanceManager.delayDistanceManagerTick = true;
+        priorities.long2IntEntrySet().fastForEach(entry -> distanceManager.markHighPriority(new ChunkPos(entry.getLongKey()), entry.getIntValue()));
+        distanceManager.delayDistanceManagerTick = false;
+        level.getChunkSource().runDistanceManagerUpdates();
+
+    }
+
+    private boolean shouldSkipPrioritization(ChunkPos coord) {
+        if (playerViewDistanceNoTickMap.getObjectsInRange(coord.toLong()) == null) return true;
+        ChunkHolder chunk = getUpdatingChunkIfPresent(coord.toLong());
+        return chunk != null && (chunk.isFullChunkReady());
+    }
+    // Paper end
     public void updatePlayerMobTypeMap(Entity entity) {
         if (!this.level.paperConfig.perPlayerMobSpawns) {
             return;
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         List<CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>>> list = Lists.newArrayList();
         int j = centerChunk.x;
         int k = centerChunk.z;
+        ChunkHolder requestingNeighbor = getUpdatingChunkIfPresent(centerChunk.toLong()); // Paper
 
         for (int l = -margin; l <= margin; ++l) {
             for (int i1 = -margin; i1 <= margin; ++i1) {
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
 
                 ChunkStatus chunkstatus = (ChunkStatus) distanceToStatus.apply(j1);
                 CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> completablefuture = playerchunk.getOrScheduleFuture(chunkstatus, this);
+                // Paper start
+                if (requestingNeighbor != null && requestingNeighbor != playerchunk && !completablefuture.isDone()) {
+                    requestingNeighbor.onNeighborRequest(playerchunk, chunkstatus);
+                    completablefuture.thenAccept(either -> {
+                        requestingNeighbor.onNeighborDone(playerchunk, chunkstatus, either.left().orElse(null));
+                    });
+                }
+                // Paper end
 
                 list.add(completablefuture);
             }
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
         };
 
         CompletableFuture<CompoundTag> chunkSaveFuture = this.level.asyncChunkTaskManager.getChunkSaveFuture(pos.x, pos.z);
+        ChunkHolder playerChunk = getUpdatingChunkIfPresent(pos.toLong());
+        int chunkPriority = playerChunk != null ? playerChunk.getQueueLevel() : 33;
+        int priority = com.destroystokyo.paper.io.PrioritizedTaskQueue.NORMAL_PRIORITY;
+
+        if (chunkPriority <= 10) {
+            priority = com.destroystokyo.paper.io.PrioritizedTaskQueue.HIGHEST_PRIORITY;
+        } else if (chunkPriority <= 20) {
+            priority = com.destroystokyo.paper.io.PrioritizedTaskQueue.HIGH_PRIORITY;
+        }
+        boolean isHighestPriority = priority == com.destroystokyo.paper.io.PrioritizedTaskQueue.HIGHEST_PRIORITY;
         if (chunkSaveFuture != null) {
-            this.level.asyncChunkTaskManager.scheduleChunkLoad(pos.x, pos.z,
-                com.destroystokyo.paper.io.PrioritizedTaskQueue.HIGH_PRIORITY, chunkHolderConsumer, false, chunkSaveFuture);
-            this.level.asyncChunkTaskManager.raisePriority(pos.x, pos.z, com.destroystokyo.paper.io.PrioritizedTaskQueue.HIGH_PRIORITY);
+            this.level.asyncChunkTaskManager.scheduleChunkLoad(pos.x, pos.z, priority, chunkHolderConsumer, isHighestPriority, chunkSaveFuture);
         } else {
-            this.level.asyncChunkTaskManager.scheduleChunkLoad(pos.x, pos.z,
-                com.destroystokyo.paper.io.PrioritizedTaskQueue.NORMAL_PRIORITY, chunkHolderConsumer, false);
+            this.level.asyncChunkTaskManager.scheduleChunkLoad(pos.x, pos.z, priority, chunkHolderConsumer, isHighestPriority);
         }
+        this.level.asyncChunkTaskManager.raisePriority(pos.x, pos.z, priority);
         return ret;
         // Paper end
     }
@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
             long i = playerchunk.getPos().toLong();
 
             Objects.requireNonNull(playerchunk);
-            mailbox.tell(ChunkTaskPriorityQueueSorter.message(runnable, i, playerchunk::getTicketLevel));
+            mailbox.tell(ChunkTaskPriorityQueueSorter.message(runnable, i, () -> 1)); // Paper - final loads are always urgent!
         });
     }
 
diff --git a/src/main/java/net/minecraft/server/level/DistanceManager.java b/src/main/java/net/minecraft/server/level/DistanceManager.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/DistanceManager.java
+++ b/src/main/java/net/minecraft/server/level/DistanceManager.java
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
     }
 
     private static int getTicketLevelAt(SortedArraySet<Ticket<?>> arraysetsorted) {
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::getLowestTicketLevel"); // Paper
         return !arraysetsorted.isEmpty() ? ((Ticket) arraysetsorted.first()).getTicketLevel() : ChunkMap.MAX_CHUNK_DISTANCE + 1;
     }
 
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
 
     public boolean runAllUpdates(ChunkMap playerchunkmap) {
         //this.f.a(); // Paper - no longer used
+        org.spigotmc.AsyncCatcher.catchOp("DistanceManagerTick"); // Paper
         this.playerTicketManager.runAllUpdates();
         int i = Integer.MAX_VALUE - this.ticketTracker.runDistanceUpdates(Integer.MAX_VALUE);
         boolean flag = i != 0;
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
 
         // Paper start
         if (!this.pendingChunkUpdates.isEmpty()) {
+            this.pollingPendingChunkUpdates = true; try {
             while(!this.pendingChunkUpdates.isEmpty()) {
                 ChunkHolder remove = this.pendingChunkUpdates.remove();
                 remove.isUpdateQueued = false;
                 remove.updateFutures(playerchunkmap, this.mainThreadExecutor);
             }
+            } finally { this.pollingPendingChunkUpdates = false; }
             // Paper end
             return true;
         } else {
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
             return flag;
         }
     }
+    boolean pollingPendingChunkUpdates = false; // Paper
 
     boolean addTicket(long i, Ticket<?> ticket) { // CraftBukkit - void -> boolean
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::addTicket"); // Paper
         SortedArraySet<Ticket<?>> arraysetsorted = this.getTickets(i);
         int j = DistanceManager.getTicketLevelAt(arraysetsorted);
         Ticket<?> ticket1 = (Ticket) arraysetsorted.addOrGet(ticket); // CraftBukkit - decompile error
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
     }
 
     boolean removeTicket(long i, Ticket<?> ticket) { // CraftBukkit - void -> boolean
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::removeTicket"); // Paper
         SortedArraySet<Ticket<?>> arraysetsorted = this.getTickets(i);
+        int oldLevel = getTicketLevelAt(arraysetsorted); // Paper
 
         boolean removed = false; // CraftBukkit
         if (arraysetsorted.remove(ticket)) {
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
             this.tickets.remove(i);
         }
 
-        this.ticketTracker.update(i, DistanceManager.getTicketLevelAt(arraysetsorted), false);
+        int newLevel = getTicketLevelAt(arraysetsorted); // Paper
+        if (newLevel > oldLevel) this.ticketTracker.update(i, newLevel, false); // Paper
         return removed; // CraftBukkit
     }
 
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
         this.addTicketAtLevel(type, pos, level, argument);
     }
 
+    // Paper start
+    public static final int PRIORITY_TICKET_LEVEL = ChunkMap.MAX_CHUNK_DISTANCE;
+    public static final int URGENT_PRIORITY = 29;
+    public boolean delayDistanceManagerTick = false;
+    public boolean markUrgent(ChunkPos coords) {
+        return addPriorityTicket(coords, TicketType.URGENT, URGENT_PRIORITY);
+    }
+    public boolean markHighPriority(ChunkPos coords, int priority) {
+        priority = Math.min(URGENT_PRIORITY - 1, Math.max(1, priority));
+        return addPriorityTicket(coords, TicketType.PRIORITY, priority);
+    }
+
+    public void markAreaHighPriority(ChunkPos center, int priority, int radius) {
+        delayDistanceManagerTick = true;
+        priority = Math.min(URGENT_PRIORITY - 1, Math.max(1, priority));
+        int finalPriority = priority;
+        net.minecraft.server.MCUtil.getSpiralOutChunks(center.getWorldPosition(), radius).forEach(coords -> {
+            addPriorityTicket(coords, TicketType.PRIORITY, finalPriority);
+        });
+        delayDistanceManagerTick = false;
+        chunkMap.level.getChunkSource().runDistanceManagerUpdates();
+    }
+
+    public void clearAreaPriorityTickets(ChunkPos center, int radius) {
+        delayDistanceManagerTick = true;
+        net.minecraft.server.MCUtil.getSpiralOutChunks(center.getWorldPosition(), radius).forEach(coords -> {
+            this.removeTicket(coords.toLong(), new Ticket<ChunkPos>(TicketType.PRIORITY, PRIORITY_TICKET_LEVEL, coords));
+        });
+        delayDistanceManagerTick = false;
+        chunkMap.level.getChunkSource().runDistanceManagerUpdates();
+    }
+
+    private boolean hasPlayerTicket(ChunkPos coords, int level) {
+        SortedArraySet<Ticket<?>> tickets = this.tickets.get(coords.toLong());
+        if (tickets == null || tickets.isEmpty()) {
+            return false;
+        }
+        for (Ticket<?> ticket : tickets) {
+            if (ticket.getType() == TicketType.PLAYER && ticket.getTicketLevel() == level) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private boolean addPriorityTicket(ChunkPos coords, TicketType<ChunkPos> ticketType, int priority) {
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::addPriorityTicket");
+        long pair = coords.toLong();
+        ChunkHolder chunk = chunkMap.getUpdatingChunkIfPresent(pair);
+        boolean needsTicket = chunkMap.playerViewDistanceNoTickMap.getObjectsInRange(pair) != null && !hasPlayerTicket(coords, 33);
+
+        if (needsTicket) {
+            Ticket<?> ticket = new Ticket<>(TicketType.PLAYER, 33, coords);
+            ticketsToRelease.add(pair);
+            addTicket(pair, ticket);
+        }
+        if ((chunk != null && chunk.isFullChunkReady())) {
+            if (needsTicket) {
+                chunkMap.level.getChunkSource().runDistanceManagerUpdates();
+            }
+            return needsTicket;
+        }
+
+        boolean success;
+        if (!(success = updatePriorityTicket(coords, ticketType, priority))) {
+            Ticket<ChunkPos> ticket = new Ticket<ChunkPos>(ticketType, PRIORITY_TICKET_LEVEL, coords);
+            ticket.priority = priority;
+            success = this.addTicket(pair, ticket);
+        } else {
+            if (chunk == null) {
+                chunk = chunkMap.getUpdatingChunkIfPresent(pair);
+            }
+            chunkMap.queueHolderUpdate(chunk);
+        }
+
+        //chunkMap.world.getWorld().spawnParticle(priority <= 15 ? org.bukkit.Particle.EXPLOSION_HUGE : org.bukkit.Particle.EXPLOSION_NORMAL, chunkMap.world.getWorld().getPlayers(), null, coords.x << 4, 70, coords.z << 4, 2, 0, 0, 0, 1, null, true);
+
+        chunkMap.level.getChunkSource().runDistanceManagerUpdates();
+
+        return success;
+    }
+
+    private boolean updatePriorityTicket(ChunkPos coords, TicketType<ChunkPos> type, int priority) {
+        SortedArraySet<Ticket<?>> tickets = this.tickets.get(coords.toLong());
+        if (tickets == null) {
+            return false;
+        }
+        for (Ticket<?> ticket : tickets) {
+            if (ticket.getType() == type) {
+                // We only support increasing, not decreasing, too complicated
+                ticket.setCurrentTick(this.ticketTickCounter);
+                ticket.priority = Math.max(ticket.priority, priority);
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public int getChunkPriority(ChunkPos coords) {
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::getChunkPriority");
+        SortedArraySet<Ticket<?>> tickets = this.tickets.get(coords.toLong());
+        if (tickets == null) {
+            return 0;
+        }
+        for (Ticket<?> ticket : tickets) {
+            if (ticket.getType() == TicketType.URGENT) {
+                return URGENT_PRIORITY;
+            }
+        }
+        for (Ticket<?> ticket : tickets) {
+            if (ticket.getType() == TicketType.PRIORITY && ticket.priority > 0) {
+                return ticket.priority;
+            }
+        }
+        return 0;
+    }
+
+    public void clearPriorityTickets(ChunkPos coords) {
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::clearPriority");
+        this.removeTicket(coords.toLong(), new Ticket<ChunkPos>(TicketType.PRIORITY, PRIORITY_TICKET_LEVEL, coords));
+    }
+
+    public void clearUrgent(ChunkPos coords) {
+        org.spigotmc.AsyncCatcher.catchOp("ChunkMapDistance::clearUrgent");
+        this.removeTicket(coords.toLong(), new Ticket<ChunkPos>(TicketType.URGENT, PRIORITY_TICKET_LEVEL, coords));
+    }
+    // Paper end
     public <T> boolean addTicketAtLevel(TicketType<T> ticketType, ChunkPos chunkcoordintpair, int level, T identifier) {
         return this.addTicket(chunkcoordintpair.toLong(), new Ticket<>(ticketType, level, identifier));
         // CraftBukkit end
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
 
         public void updateViewDistance(int watchDistance) {
             ObjectIterator objectiterator = this.chunks.long2ByteEntrySet().iterator();
+            // Paper start - set the view distance before scheduling chunk loads/unloads
+            int lastViewDistance = viewDistance;
+            this.viewDistance = watchDistance;
+            // Paper end
 
             while (objectiterator.hasNext()) {
                 it.unimi.dsi.fastutil.longs.Long2ByteMap.Entry it_unimi_dsi_fastutil_longs_long2bytemap_entry = (it.unimi.dsi.fastutil.longs.Long2ByteMap.Entry) objectiterator.next();
                 byte b0 = it_unimi_dsi_fastutil_longs_long2bytemap_entry.getByteValue();
                 long j = it_unimi_dsi_fastutil_longs_long2bytemap_entry.getLongKey();
 
-                this.onLevelChange(j, b0, this.haveTicketFor(b0), b0 <= watchDistance - 2);
+                this.onLevelChange(j, b0, b0 <= lastViewDistance - 2, this.haveTicketFor(b0)); // Paper
             }
 
-            this.viewDistance = watchDistance;
+            //this.e = i; // Paper - view distance is now set further up
         }
 
         private void onLevelChange(long pos, int distance, boolean oldWithinViewDistance, boolean withinViewDistance) {
             if (oldWithinViewDistance != withinViewDistance) {
-                Ticket<?> ticket = new Ticket<>(TicketType.PLAYER, 33, new ChunkPos(pos)); // Paper - no-tick view distance
+                ChunkPos coords = new ChunkPos(pos); // Paper
+                Ticket<?> ticket = new Ticket<>(TicketType.PLAYER, 33, coords); // Paper - no-tick view distance
 
                 if (withinViewDistance) {
-                    DistanceManager.this.ticketThrottlerInput.tell(ChunkTaskPriorityQueueSorter.message(() -> {
+                    scheduleChunkLoad(pos, net.minecraft.server.MinecraftServer.currentTick, distance, (priority) -> { // Paper - smarter ticket delay based on frustum and distance
+                    // Paper start - recheck its still valid if not cancel
+                    if (!isChunkInRange(pos)) {
+                        DistanceManager.this.ticketThrottlerReleaser.tell(ChunkTaskPriorityQueueSorter.release(() -> {
+                            DistanceManager.this.mainThreadExecutor.execute(() -> {
+                                DistanceManager.this.removeTicket(pos, ticket);
+                                DistanceManager.this.clearPriorityTickets(coords);
+                            });
+                        }, pos, false));
+                        return;
+                    }
+                    // abort early if we got a ticket already
+                    if (hasPlayerTicket(coords, 33)) return;
+                    // skip player ticket throttle for near chunks
+                    if (priority <= 3) {
+                        DistanceManager.this.addTicket(pos, ticket);
+                        DistanceManager.this.ticketsToRelease.add(pos);
+                        return;
+                    }
+                    // Paper end
+                    DistanceManager.this.ticketThrottlerInput.tell(ChunkTaskPriorityQueueSorter.message(() -> { // CraftBukkit - decompile error
                         DistanceManager.this.mainThreadExecutor.execute(() -> {
-                            if (this.haveTicketFor(this.getLevel(pos))) {
+                            if (isChunkInRange(pos)) { if (!hasPlayerTicket(coords, 33)) { // Paper - high priority might of already added it
                                 DistanceManager.this.addTicket(pos, ticket);
                                 DistanceManager.this.ticketsToRelease.add(pos);
-                            } else {
-                                DistanceManager.this.ticketThrottlerReleaser.tell(ChunkTaskPriorityQueueSorter.release(() -> {
+                            }} else { // Paper
+                                DistanceManager.this.ticketThrottlerReleaser.tell(ChunkTaskPriorityQueueSorter.release(() -> { // CraftBukkit - decompile error
                                 }, pos, false));
                             }
 
                         });
                     }, pos, () -> {
-                        return distance;
+                        return Math.min(ChunkMap.MAX_CHUNK_DISTANCE, priority); // Paper
                     }));
+                    }); // Paper
                 } else {
                     DistanceManager.this.ticketThrottlerReleaser.tell(ChunkTaskPriorityQueueSorter.release(() -> {
                         DistanceManager.this.mainThreadExecutor.execute(() -> {
                             DistanceManager.this.removeTicket(pos, ticket);
+                            DistanceManager.this.clearPriorityTickets(coords); // Paper
                         });
                     }, pos, true));
                 }
@@ -0,0 +0,0 @@ public abstract class DistanceManager {
 
         }
 
+        // Paper start - smart scheduling of player tickets
+        private boolean isChunkInRange(long i) {
+            return this.haveTicketFor(this.getLevel(i));
+        }
+        public void scheduleChunkLoad(long i, long startTick, int initialDistance, java.util.function.Consumer<Integer> task) {
+            long elapsed = net.minecraft.server.MinecraftServer.currentTick - startTick;
+            ChunkPos chunkPos = new ChunkPos(i);
+            ChunkHolder updatingChunk = chunkMap.getUpdatingChunkIfPresent(i);
+            if ((updatingChunk != null && updatingChunk.isFullChunkReady()) || !isChunkInRange(i) || getChunkPriority(chunkPos) > 0) { // Copied from above
+                // no longer needed
+                task.accept(1);
+                return;
+            }
+
+            int desireDelay = 0;
+            double minDist = Double.MAX_VALUE;
+            com.destroystokyo.paper.util.misc.PooledLinkedHashSets.PooledObjectLinkedOpenHashSet<ServerPlayer> players = chunkMap.playerViewDistanceNoTickMap.getObjectsInRange(i);
+            if (elapsed == 0 && initialDistance <= 4) {
+                // Aim for no delay on initial 6 chunk radius tickets save on performance of the below code to only > 6
+                minDist = initialDistance;
+            } else if (players != null) {
+                Object[] backingSet = players.getBackingSet();
+
+                net.minecraft.core.BlockPos blockPos = chunkPos.getWorldPosition();
+
+                boolean isFront = false;
+                net.minecraft.core.BlockPos.MutableBlockPos pos = new net.minecraft.core.BlockPos.MutableBlockPos();
+                for (int index = 0, len = backingSet.length; index < len; ++index) {
+                    if (!(backingSet[index] instanceof ServerPlayer)) {
+                        continue;
+                    }
+                    ServerPlayer player = (ServerPlayer) backingSet[index];
+
+                    ChunkPos pointInFront = player.getChunkInFront(5);
+                    pos.setValues(pointInFront.x << 4, 0, pointInFront.z << 4);
+                    double frontDist = net.minecraft.server.MCUtil.distanceSq(pos, blockPos);
+
+                    pos.setValues(player.getX(), 0, player.getZ());
+                    double center = net.minecraft.server.MCUtil.distanceSq(pos, blockPos);
+
+                    double dist = Math.min(frontDist, center);
+                    if (!isFront) {
+                        ChunkPos pointInBack = player.getChunkInFront(-7);
+                        pos.setValues(pointInBack.x << 4, 0, pointInBack.z << 4);
+                        double backDist = net.minecraft.server.MCUtil.distanceSq(pos, blockPos);
+                        if (frontDist < backDist) {
+                            isFront = true;
+                        }
+                    }
+                    if (dist < minDist) {
+                        minDist = dist;
+                    }
+                }
+                if (minDist == Double.MAX_VALUE) {
+                    minDist = 15;
+                } else {
+                    minDist = Math.sqrt(minDist) / 16;
+                }
+                if (minDist > 4) {
+                    int desiredTimeDelayMax = isFront ?
+                        (minDist < 10 ? 7 : 15) : // Front
+                        (minDist < 10 ? 15 : 45); // Back
+                    desireDelay += (desiredTimeDelayMax * 20) * (minDist / 32);
+                }
+            } else {
+                minDist = initialDistance;
+                desireDelay = 1;
+            }
+            long delay = desireDelay - elapsed;
+            if (delay <= 0 && minDist > 4 && minDist < Double.MAX_VALUE) {
+                boolean hasAnyNeighbor = false;
+                for (int x = -1; x <= 1; x++) {
+                    for (int z = -1; z <= 1; z++) {
+                        if (x == 0 && z == 0) continue;
+                        long pair = ChunkPos.asLong(chunkPos.x + x, chunkPos.z + z);
+                        ChunkHolder neighbor = chunkMap.getUpdatingChunkIfPresent(pair);
+                        ChunkStatus current = neighbor != null ? neighbor.getChunkHolderStatus() : null;
+                        if (current != null && current.isOrAfter(ChunkStatus.LIGHT)) {
+                            hasAnyNeighbor = true;
+                        }
+                    }
+                }
+                if (!hasAnyNeighbor) {
+                    delay += 20;
+                }
+            }
+            if (delay <= 0) {
+                task.accept((int) minDist);
+            } else {
+                int taskDelay = (int) Math.min(delay, minDist >= 10 ? 40 : (minDist < 6 ? 5 : 20));
+                net.minecraft.server.MCUtil.scheduleTask(taskDelay, () -> scheduleChunkLoad(i, startTick, initialDistance, task), "Player Ticket Delayer");
+            }
+        }
+        // Paper end
+
         @Override
         public void runAllUpdates() {
             super.runAllUpdates();
diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
     public <T> void removeTicketAtLevel(TicketType<T> ticketType, ChunkPos chunkPos, int ticketLevel, T identifier) {
         this.distanceManager.removeTicketAtLevel(ticketType, chunkPos, ticketLevel, identifier);
     }
+
+    public boolean markUrgent(ChunkPos coords) {
+        return this.distanceManager.markUrgent(coords);
+    }
+
+    public boolean markHighPriority(ChunkPos coords, int priority) {
+        return this.distanceManager.markHighPriority(coords, priority);
+    }
+
+    public void markAreaHighPriority(ChunkPos center, int priority, int radius) {
+        this.distanceManager.markAreaHighPriority(center, priority, radius);
+    }
+
+    public void clearAreaPriorityTickets(ChunkPos center, int radius) {
+        this.distanceManager.clearAreaPriorityTickets(center, radius);
+    }
+
+    public void clearPriorityTickets(ChunkPos coords) {
+        this.distanceManager.clearPriorityTickets(coords);
+    }
     // Paper end - async chunk io
 
     @Nullable
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
             Objects.requireNonNull(completablefuture);
             if (!completablefuture.isDone()) { // Paper
                 // Paper start - async chunk io/loading
+                ChunkPos pair = new ChunkPos(x1, z1);
+                this.distanceManager.markUrgent(pair);
                 this.level.asyncChunkTaskManager.raisePriority(x1, z1, com.destroystokyo.paper.io.PrioritizedTaskQueue.HIGHEST_PRIORITY);
                 com.destroystokyo.paper.io.chunk.ChunkTaskManager.pushChunkWait(this.level, x1, z1);
                 // Paper end
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
             chunkproviderserver_a.managedBlock(completablefuture::isDone);
                 com.destroystokyo.paper.io.chunk.ChunkTaskManager.popChunkWait(); // Paper - async chunk debug
                 this.level.timings.syncChunkLoad.stopTiming(); // Paper
+                this.distanceManager.clearPriorityTickets(pair); // Paper
+                this.distanceManager.clearUrgent(pair); // Paper
             } // Paper
             ichunkaccess = (ChunkAccess) ((Either) completablefuture.join()).map((ichunkaccess1) -> {
                 return ichunkaccess1;
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
         if (flag && !currentlyUnloading) {
             // CraftBukkit end
             this.distanceManager.addTicket(TicketType.UNKNOWN, chunkcoordintpair, l, chunkcoordintpair);
+            if (isUrgent) this.distanceManager.markUrgent(chunkcoordintpair); // Paper
             if (this.chunkAbsent(playerchunk, l)) {
                 ProfilerFiller gameprofilerfiller = this.level.getProfiler();
 
                 gameprofilerfiller.push("chunkLoad");
+                distanceManager.delayDistanceManagerTick = false; // Paper - ensure this is never false
                 this.runDistanceManagerUpdates();
                 playerchunk = this.getVisibleChunkIfPresent(k);
                 gameprofilerfiller.pop();
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
                 }
             }
         }
-
-        return this.chunkAbsent(playerchunk, l) ? ChunkHolder.UNLOADED_CHUNK_FUTURE : playerchunk.getOrScheduleFuture(chunkstatus, this.chunkMap);
+        // Paper start
+        CompletableFuture<Either<ChunkAccess, ChunkHolder.ChunkLoadingFailure>> future = this.chunkAbsent(playerchunk, l) ? ChunkHolder.UNLOADED_CHUNK_FUTURE : playerchunk.getOrScheduleFuture(chunkstatus, this.chunkMap);
+        if (isUrgent) {
+            future.thenAccept(either -> this.distanceManager.clearUrgent(chunkcoordintpair));
+        }
+        return future;
+        // Paper end
     }
 
     private boolean chunkAbsent(@Nullable ChunkHolder holder, int maxLevel) {
@@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
     }
 
     public boolean runDistanceManagerUpdates() { // Paper - packate-private -> public
+        if (distanceManager.delayDistanceManagerTick) return false; // Paper
         boolean flag = this.distanceManager.runAllUpdates(this.chunkMap);
         boolean flag1 = this.chunkMap.promoteChunkMap();
 
diff --git a/src/main/java/net/minecraft/server/level/ServerPlayer.java b/src/main/java/net/minecraft/server/level/ServerPlayer.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/ServerPlayer.java
+++ b/src/main/java/net/minecraft/server/level/ServerPlayer.java
@@ -0,0 +0,0 @@ public class ServerPlayer extends Player {
     private int lastRecordedArmor = Integer.MIN_VALUE;
     private int lastRecordedLevel = Integer.MIN_VALUE;
     private int lastRecordedExperience = Integer.MIN_VALUE;
+    public long lastHighPriorityChecked; // Paper
+    public void forceCheckHighPriority() {
+        lastHighPriorityChecked = -1;
+        getLevel().getChunkSource().chunkMap.checkHighPriorityChunks(this);
+    }
+    public boolean isRealPlayer; // Paper
     private float lastSentHealth = -1.0E8F;
     private int lastSentFood = -99999999;
     private boolean lastFoodSaturationZero = true;
@@ -0,0 +0,0 @@ public class ServerPlayer extends Player {
         this.maxHealthCache = this.getMaxHealth();
         this.cachedSingleMobDistanceMap = new com.destroystokyo.paper.util.PooledHashSets.PooledObjectLinkedOpenHashSet<>(this); // Paper
     }
+    // Paper start
+    public BlockPos getPointInFront(double inFront) {
+        double rads = Math.toRadians(net.minecraft.server.MCUtil.normalizeYaw(this.getYRot()+90)); // MC rotates yaw 90 for some odd reason
+        final double x = getX() + inFront * Math.cos(rads);
+        final double z = getZ() + inFront * Math.sin(rads);
+        return new BlockPos(x, getY(), z);
+    }
+
+    public ChunkPos getChunkInFront(double inFront) {
+        double rads = Math.toRadians(net.minecraft.server.MCUtil.normalizeYaw(this.getYRot()+90)); // MC rotates yaw 90 for some odd reason
+        final double x = getX() + (inFront * 16) * Math.cos(rads);
+        final double z = getZ() + (inFront * 16) * Math.sin(rads);
+        return new ChunkPos(Mth.floor(x) >> 4, Mth.floor(z) >> 4);
+    }
+    // Paper end
 
     // Yes, this doesn't match Vanilla, but it's the best we can do for now.
     // If this is an issue, PRs are welcome
@@ -0,0 +0,0 @@ public class ServerPlayer extends Player {
             if (valid && !this.isSpectator() || !this.touchingUnloadedChunk()) { // Paper - don't tick dead players that are not in the world currently (pending respawn)
                 super.tick();
             }
+            if (valid && isAlive() && connection != null) ((ServerLevel)level).getChunkSource().chunkMap.checkHighPriorityChunks(this); // Paper
 
             for (int i = 0; i < this.getInventory().getContainerSize(); ++i) {
                 ItemStack itemstack = this.getInventory().getItem(i);
diff --git a/src/main/java/net/minecraft/server/level/Ticket.java b/src/main/java/net/minecraft/server/level/Ticket.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/Ticket.java
+++ b/src/main/java/net/minecraft/server/level/Ticket.java
@@ -0,0 +0,0 @@ public final class Ticket<T> implements Comparable<Ticket<?>> {
     public final T key; public final T getObjectReason() { return this.key; } // Paper - OBFHELPER
     private long createdTick; public final long getCreationTick() { return this.createdTick; } // Paper - OBFHELPER
     public long delayUnloadBy; // Paper
+    public int priority = 0; // Paper
 
     protected Ticket(TicketType<T> type, int level, T argument) {
         this.type = type;
@@ -0,0 +0,0 @@ public final class Ticket<T> implements Comparable<Ticket<?>> {
         return this.ticketLevel;
     }
 
+    public final void setCurrentTick(long i) { this.setCreatedTick(i); } // Paper - OBFHELPER
     protected void setCreatedTick(long tickCreated) {
         this.createdTick = tickCreated;
     }
diff --git a/src/main/java/net/minecraft/server/level/TicketType.java b/src/main/java/net/minecraft/server/level/TicketType.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/level/TicketType.java
+++ b/src/main/java/net/minecraft/server/level/TicketType.java
@@ -0,0 +0,0 @@ import net.minecraft.world.level.ChunkPos;
 public class TicketType<T> {
     public static final TicketType<Long> FUTURE_AWAIT = create("future_await", Long::compareTo); // Paper
     public static final TicketType<Long> ASYNC_LOAD = create("async_load", Long::compareTo); // Paper
+    public static final TicketType<ChunkPos> PRIORITY = create("priority", Comparator.comparingLong(ChunkPos::toLong), 300); // Paper
+    public static final TicketType<ChunkPos> URGENT = create("urgent", Comparator.comparingLong(ChunkPos::toLong), 300); // Paper
 
     private final String name;
     private final Comparator<T> comparator;
diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
@@ -0,0 +0,0 @@ public class ServerGamePacketListenerImpl implements ServerPlayerConnection, Ser
 
         this.awaitingTeleportTime = this.tickCount;
         this.player.absMoveTo(d0, d1, d2, f, f1);
+        this.player.forceCheckHighPriority(); // Paper
         this.player.connection.send(new ClientboundPlayerPositionPacket(d0 - d3, d1 - d4, d2 - d5, f - f2, f1 - f3, set, this.awaitingTeleport, flag));
     }
 
diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/net/minecraft/server/players/PlayerList.java
+++ b/src/main/java/net/minecraft/server/players/PlayerList.java
@@ -0,0 +0,0 @@ public abstract class PlayerList {
         net.minecraft.server.level.ChunkMap playerChunkMap = worldserver1.getChunkSource().chunkMap;
         net.minecraft.server.level.DistanceManager distanceManager = playerChunkMap.distanceManager;
         distanceManager.addTicketAtLevel(net.minecraft.server.level.TicketType.LOGIN, pos, 31, pos.toLong());
-        worldserver1.getChunkSource().runDistanceManagerUpdates();
-        worldserver1.getChunkSource().getChunkAtAsynchronously(chunkX, chunkZ, true, true).thenApply(chunk -> {
+        worldserver1.getChunkSource().markAreaHighPriority(pos, 28, 3);
+        worldserver1.getChunkSource().getChunkAtAsynchronously(chunkX, chunkZ, true, false).thenApply(chunk -> {
             net.minecraft.server.level.ChunkHolder updatingChunk = playerChunkMap.getUpdatingChunkIfPresent(pos.toLong());
             if (updatingChunk != null) {
                 return updatingChunk.getEntityTickingFuture();
@@ -0,0 +0,0 @@ public abstract class PlayerList {
         SocketAddress socketaddress = loginlistener.connection.getRemoteAddress();
 
         ServerPlayer entity = new ServerPlayer(this.server, this.server.getLevel(Level.OVERWORLD), gameprofile);
+        entity.isRealPlayer = true; // Paper
         Player player = entity.getBukkitEntity();
         PlayerLoginEvent event = new PlayerLoginEvent(player, hostname, ((java.net.InetSocketAddress) socketaddress).getAddress(), ((java.net.InetSocketAddress) loginlistener.connection.getRawAddress()).getAddress());
 
@@ -0,0 +0,0 @@ public abstract class PlayerList {
         // CraftBukkit end
 
         worldserver1.getChunkSource().addRegionTicket(net.minecraft.server.level.TicketType.POST_TELEPORT, new net.minecraft.world.level.ChunkPos(location.getBlockX() >> 4, location.getBlockZ() >> 4), 1, entityplayer.getId()); // Paper
+        entityplayer1.forceCheckHighPriority(); // Player
         while (avoidSuffocation && !worldserver1.noCollision(entityplayer1) && entityplayer1.getY() < (double) worldserver1.getMaxBuildHeight()) {
             entityplayer1.setPos(entityplayer1.getX(), entityplayer1.getY() + 1.0D, entityplayer1.getZ());
         }
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -0,0 +0,0 @@ public class CraftWorld implements World {
             return future;
         }
 
+        if (!urgent) {
+            // if not urgent, at least use a slightly boosted priority
+            world.getChunkSource().markHighPriority(new ChunkPos(x, z), 1);
+        }
         return this.world.getChunkSource().getChunkAtAsynchronously(x, z, gen, urgent).thenComposeAsync((either) -> {
             net.minecraft.world.level.chunk.LevelChunk chunk = (net.minecraft.world.level.chunk.LevelChunk) either.left().orElse(null);
             if (chunk != null) addTicket(x, z); // Paper
diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
@@ -0,0 +0,0 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
         throw new UnsupportedOperationException("Cannot set rotation of players. Consider teleporting instead.");
     }
 
+    // Paper start
+    @Override
+    public java.util.concurrent.CompletableFuture<Boolean> teleportAsync(Location loc, @javax.annotation.Nonnull PlayerTeleportEvent.TeleportCause cause) {
+        ((CraftWorld)loc.getWorld()).getHandle().getChunkSource().markAreaHighPriority(new net.minecraft.world.level.ChunkPos(net.minecraft.util.Mth.floor(loc.getX()) >> 4, net.minecraft.util.Mth.floor(loc.getZ()) >> 4), 28, 3); // Paper - load area high priority
+        return super.teleportAsync(loc, cause);
+    }
+    // Paper end
     @Override
     public boolean teleport(Location location, PlayerTeleportEvent.TeleportCause cause) {
         Preconditions.checkArgument(location != null, "location");
