papermc/patches/server/0735-Rewrite-entity-bounding-box-lookup-calls.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Thu, 17 Jun 2021 19:55:02 -0700
Subject: [PATCH] Rewrite entity bounding box lookup calls

For whatever reason, Mojang thought it was OK to make this system
scale logn relative to the number of entity sections loaded.
On top of that, they do a hashtable lookup per section - before
this was just a basic array access.

This patch brings back entity slices for lookup only.

diff --git a/src/main/java/io/papermc/paper/world/ChunkEntitySlices.java b/src/main/java/io/papermc/paper/world/ChunkEntitySlices.java
new file mode 100644
index 0000000000000000000000000000000000000000..47b5f75d9f27cf3ab947fd1f69cbd609fb9f2749
--- /dev/null
+++ b/src/main/java/io/papermc/paper/world/ChunkEntitySlices.java
@@ -0,0 +1,500 @@
+package io.papermc.paper.world;
+
+import com.destroystokyo.paper.util.maplist.EntityList;
+import it.unimi.dsi.fastutil.objects.Reference2ObjectMap;
+import it.unimi.dsi.fastutil.objects.Reference2ObjectOpenHashMap;
+import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.util.Mth;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.entity.boss.EnderDragonPart;
+import net.minecraft.world.entity.boss.enderdragon.EnderDragon;
+import net.minecraft.world.phys.AABB;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Predicate;
+
+public final class ChunkEntitySlices {
+
+    protected final int minSection;
+    protected final int maxSection;
+    protected final int chunkX;
+    protected final int chunkZ;
+    protected final ServerLevel world;
+
+    protected final EntityCollectionBySection allEntities;
+    protected final EntityCollectionBySection hardCollidingEntities;
+    protected final Reference2ObjectOpenHashMap<Class<? extends Entity>, EntityCollectionBySection> entitiesByClass;
+    protected final EntityList entities = new EntityList();
+
+    public ChunkHolder.FullChunkStatus status;
+
+    // TODO implement container search optimisations
+
+    public ChunkEntitySlices(final ServerLevel world, final int chunkX, final int chunkZ, final ChunkHolder.FullChunkStatus status,
+                             final int minSection, final int maxSection) { // inclusive, inclusive
+        this.minSection = minSection;
+        this.maxSection = maxSection;
+        this.chunkX = chunkX;
+        this.chunkZ = chunkZ;
+        this.world = world;
+
+        this.allEntities = new EntityCollectionBySection(this);
+        this.hardCollidingEntities = new EntityCollectionBySection(this);
+        this.entitiesByClass = new Reference2ObjectOpenHashMap<>();
+
+        this.status = status;
+    }
+
+    // Paper start - optimise CraftChunk#getEntities
+    public org.bukkit.entity.Entity[] getChunkEntities() {
+        List<org.bukkit.entity.Entity> ret = new java.util.ArrayList<>();
+        final Entity[] entities = this.entities.getRawData();
+        for (int i = 0, size = Math.min(entities.length, this.entities.size()); i < size; ++i) {
+            final Entity entity = entities[i];
+            if (entity == null) {
+                continue;
+            }
+            final org.bukkit.entity.Entity bukkit = entity.getBukkitEntity();
+            if (bukkit != null && bukkit.isValid()) {
+                ret.add(bukkit);
+            }
+        }
+
+        return ret.toArray(new org.bukkit.entity.Entity[0]);
+    }
+    // Paper end - optimise CraftChunk#getEntities
+
+    public boolean isEmpty() {
+        return this.entities.size() == 0;
+    }
+
+    private void updateTicketLevels() {
+        final Entity[] entities = this.entities.getRawData();
+        for (int i = 0, size = Math.min(entities.length, this.entities.size()); i < size; ++i) {
+            final Entity entity = entities[i];
+            entity.chunkStatus = this.status;
+        }
+    }
+
+    public synchronized void updateStatus(final ChunkHolder.FullChunkStatus status) {
+        this.status = status;
+        this.updateTicketLevels();
+    }
+
+    public synchronized void addEntity(final Entity entity, final int chunkSection) {
+        if (!this.entities.add(entity)) {
+            return;
+        }
+        entity.chunkStatus = this.status;
+        final int sectionIndex = chunkSection - this.minSection;
+
+        this.allEntities.addEntity(entity, sectionIndex);
+
+        if (entity.hardCollides()) {
+            this.hardCollidingEntities.addEntity(entity, sectionIndex);
+        }
+
+        for (final Iterator<Reference2ObjectMap.Entry<Class<? extends Entity>, EntityCollectionBySection>> iterator =
+             this.entitiesByClass.reference2ObjectEntrySet().fastIterator(); iterator.hasNext();) {
+            final Reference2ObjectMap.Entry<Class<? extends Entity>, EntityCollectionBySection> entry = iterator.next();
+
+            if (entry.getKey().isInstance(entity)) {
+                entry.getValue().addEntity(entity, sectionIndex);
+            }
+        }
+    }
+
+    public synchronized void removeEntity(final Entity entity, final int chunkSection) {
+        if (!this.entities.remove(entity)) {
+            return;
+        }
+        entity.chunkStatus = ChunkHolder.FullChunkStatus.INACCESSIBLE;
+        final int sectionIndex = chunkSection - this.minSection;
+
+        this.allEntities.removeEntity(entity, sectionIndex);
+
+        if (entity.hardCollides()) {
+            this.hardCollidingEntities.removeEntity(entity, sectionIndex);
+        }
+
+        for (final Iterator<Reference2ObjectMap.Entry<Class<? extends Entity>, EntityCollectionBySection>> iterator =
+             this.entitiesByClass.reference2ObjectEntrySet().fastIterator(); iterator.hasNext();) {
+            final Reference2ObjectMap.Entry<Class<? extends Entity>, EntityCollectionBySection> entry = iterator.next();
+
+            if (entry.getKey().isInstance(entity)) {
+                entry.getValue().removeEntity(entity, sectionIndex);
+            }
+        }
+    }
+
+    public void getHardCollidingEntities(final Entity except, final AABB box, final List<Entity> into, final Predicate<? super Entity> predicate) {
+        this.hardCollidingEntities.getEntities(except, box, into, predicate);
+    }
+
+    public void getEntities(final Entity except, final AABB box, final List<Entity> into, final Predicate<? super Entity> predicate) {
+        this.allEntities.getEntitiesWithEnderDragonParts(except, box, into, predicate);
+    }
+
+    public <T extends Entity> void getEntities(final EntityType<?> type, final AABB box, final List<? super T> into,
+                                               final Predicate<? super T> predicate) {
+        this.allEntities.getEntities(type, box, (List)into, (Predicate)predicate);
+    }
+
+    protected EntityCollectionBySection initClass(final Class<? extends Entity> clazz) {
+        final EntityCollectionBySection ret = new EntityCollectionBySection(this);
+
+        for (int sectionIndex = 0; sectionIndex < this.allEntities.entitiesBySection.length; ++sectionIndex) {
+            final BasicEntityList<Entity> sectionEntities = this.allEntities.entitiesBySection[sectionIndex];
+            if (sectionEntities == null) {
+                continue;
+            }
+
+            final Entity[] storage = sectionEntities.storage;
+
+            for (int i = 0, len = Math.min(storage.length, sectionEntities.size()); i < len; ++i) {
+                final Entity entity = storage[i];
+
+                if (clazz.isInstance(entity)) {
+                    ret.addEntity(entity, sectionIndex);
+                }
+            }
+        }
+
+        return ret;
+    }
+
+    public <T extends Entity> void getEntities(final Class<? extends T> clazz, final Entity except, final AABB box, final List<? super T> into,
+                                               final Predicate<? super T> predicate) {
+        EntityCollectionBySection collection = this.entitiesByClass.get(clazz);
+        if (collection != null) {
+            collection.getEntitiesWithEnderDragonParts(except, clazz, box, (List)into, (Predicate)predicate);
+        } else {
+            synchronized (this) {
+                this.entitiesByClass.putIfAbsent(clazz, collection = this.initClass(clazz));
+            }
+            collection.getEntitiesWithEnderDragonParts(except, clazz, box, (List)into, (Predicate)predicate);
+        }
+    }
+
+    public synchronized void updateEntity(final Entity entity) {
+        /*// TODO
+        if (prev aabb != entity.getBoundingBox()) {
+            this.entityMap.delete(entity, prev aabb);
+            this.entityMap.insert(entity, prev aabb = entity.getBoundingBox());
+        }*/
+    }
+
+    protected static final class BasicEntityList<E extends Entity> {
+
+        protected static final Entity[] EMPTY = new Entity[0];
+        protected static final int DEFAULT_CAPACITY = 4;
+
+        protected E[] storage;
+        protected int size;
+
+        public BasicEntityList() {
+            this(0);
+        }
+
+        public BasicEntityList(final int cap) {
+            this.storage = (E[])(cap <= 0 ? EMPTY : new Entity[cap]);
+        }
+
+        public boolean isEmpty() {
+            return this.size == 0;
+        }
+
+        public int size() {
+            return this.size;
+        }
+
+        private void resize() {
+            if (this.storage == EMPTY) {
+                this.storage = (E[])new Entity[DEFAULT_CAPACITY];
+            } else {
+                this.storage = Arrays.copyOf(this.storage, this.storage.length * 2);
+            }
+        }
+
+        public void add(final E entity) {
+            final int idx = this.size++;
+            if (idx >= this.storage.length) {
+                this.resize();
+                this.storage[idx] = entity;
+            } else {
+                this.storage[idx] = entity;
+            }
+        }
+
+        public int indexOf(final E entity) {
+            final E[] storage = this.storage;
+
+            for (int i = 0, len = Math.min(this.storage.length, this.size); i < len; ++i) {
+                if (storage[i] == entity) {
+                    return i;
+                }
+            }
+
+            return -1;
+        }
+
+        public boolean remove(final E entity) {
+            final int idx = this.indexOf(entity);
+            if (idx == -1) {
+                return false;
+            }
+
+            final int size = --this.size;
+            final E[] storage = this.storage;
+            if (idx != size) {
+                System.arraycopy(storage, idx + 1, storage, idx, size - idx);
+            }
+
+            storage[size] = null;
+
+            return true;
+        }
+
+        public boolean has(final E entity) {
+            return this.indexOf(entity) != -1;
+        }
+    }
+
+    protected static final class EntityCollectionBySection {
+
+        protected final ChunkEntitySlices manager;
+        protected final long[] nonEmptyBitset;
+        protected final BasicEntityList<Entity>[] entitiesBySection;
+        protected int count;
+
+        public EntityCollectionBySection(final ChunkEntitySlices manager) {
+            this.manager = manager;
+
+            final int sectionCount = manager.maxSection - manager.minSection + 1;
+
+            this.nonEmptyBitset = new long[(sectionCount + (Long.SIZE - 1)) >>> 6]; // (sectionCount + (Long.SIZE - 1)) / Long.SIZE
+            this.entitiesBySection = new BasicEntityList[sectionCount];
+        }
+
+        public void addEntity(final Entity entity, final int sectionIndex) {
+            BasicEntityList<Entity> list = this.entitiesBySection[sectionIndex];
+
+            if (list != null && list.has(entity)) {
+                return;
+            }
+
+            if (list == null) {
+                this.entitiesBySection[sectionIndex] = list = new BasicEntityList<>();
+                this.nonEmptyBitset[sectionIndex >>> 6] |= (1L << (sectionIndex & (Long.SIZE - 1)));
+            }
+
+            list.add(entity);
+            ++this.count;
+        }
+
+        public void removeEntity(final Entity entity, final int sectionIndex) {
+            final BasicEntityList<Entity> list = this.entitiesBySection[sectionIndex];
+
+            if (list == null || !list.remove(entity)) {
+                return;
+            }
+
+            --this.count;
+
+            if (list.isEmpty()) {
+                this.entitiesBySection[sectionIndex] = null;
+                this.nonEmptyBitset[sectionIndex >>> 6] ^= (1L << (sectionIndex & (Long.SIZE - 1)));
+            }
+        }
+
+        public void getEntities(final Entity except, final AABB box, final List<Entity> into, final Predicate<? super Entity> predicate) {
+            if (this.count == 0) {
+                return;
+            }
+
+            final int minSection = this.manager.minSection;
+            final int maxSection = this.manager.maxSection;
+
+            final int min = Mth.clamp(Mth.floor(box.minY - 2.0) >> 4, minSection, maxSection);
+            final int max = Mth.clamp(Mth.floor(box.maxY + 2.0) >> 4, minSection, maxSection);
+
+            // TODO use the bitset
+
+            final BasicEntityList<Entity>[] entitiesBySection = this.entitiesBySection;
+
+            for (int section = min; section <= max; ++section) {
+                final BasicEntityList<Entity> list = entitiesBySection[section - minSection];
+
+                if (list == null) {
+                    continue;
+                }
+
+                final Entity[] storage = list.storage;
+
+                for (int i = 0, len = Math.min(storage.length, list.size()); i < len; ++i) {
+                    final Entity entity = storage[i];
+
+                    if (entity == null || entity == except || !entity.getBoundingBox().intersects(box)) {
+                        continue;
+                    }
+
+                    if (predicate != null && !predicate.test(entity)) {
+                        continue;
+                    }
+
+                    into.add(entity);
+                }
+            }
+        }
+
+        public void getEntitiesWithEnderDragonParts(final Entity except, final AABB box, final List<Entity> into,
+                                                    final Predicate<? super Entity> predicate) {
+            if (this.count == 0) {
+                return;
+            }
+
+            final int minSection = this.manager.minSection;
+            final int maxSection = this.manager.maxSection;
+
+            final int min = Mth.clamp(Mth.floor(box.minY - 2.0) >> 4, minSection, maxSection);
+            final int max = Mth.clamp(Mth.floor(box.maxY + 2.0) >> 4, minSection, maxSection);
+
+            // TODO use the bitset
+
+            final BasicEntityList<Entity>[] entitiesBySection = this.entitiesBySection;
+
+            for (int section = min; section <= max; ++section) {
+                final BasicEntityList<Entity> list = entitiesBySection[section - minSection];
+
+                if (list == null) {
+                    continue;
+                }
+
+                final Entity[] storage = list.storage;
+
+                for (int i = 0, len = Math.min(storage.length, list.size()); i < len; ++i) {
+                    final Entity entity = storage[i];
+
+                    if (entity == null || entity == except || !entity.getBoundingBox().intersects(box)) {
+                        continue;
+                    }
+
+                    if (predicate == null || predicate.test(entity)) {
+                        into.add(entity);
+                    } // else: continue to test the ender dragon parts
+
+                    if (entity instanceof EnderDragon) {
+                        for (final EnderDragonPart part : ((EnderDragon)entity).subEntities) {
+                            if (part == except || !part.getBoundingBox().intersects(box)) {
+                                continue;
+                            }
+
+                            if (predicate != null && !predicate.test(part)) {
+                                continue;
+                            }
+
+                            into.add(part);
+                        }
+                    }
+                }
+            }
+        }
+
+        public void getEntitiesWithEnderDragonParts(final Entity except, final Class<?> clazz, final AABB box, final List<Entity> into,
+                                                    final Predicate<? super Entity> predicate) {
+            if (this.count == 0) {
+                return;
+            }
+
+            final int minSection = this.manager.minSection;
+            final int maxSection = this.manager.maxSection;
+
+            final int min = Mth.clamp(Mth.floor(box.minY - 2.0) >> 4, minSection, maxSection);
+            final int max = Mth.clamp(Mth.floor(box.maxY + 2.0) >> 4, minSection, maxSection);
+
+            // TODO use the bitset
+
+            final BasicEntityList<Entity>[] entitiesBySection = this.entitiesBySection;
+
+            for (int section = min; section <= max; ++section) {
+                final BasicEntityList<Entity> list = entitiesBySection[section - minSection];
+
+                if (list == null) {
+                    continue;
+                }
+
+                final Entity[] storage = list.storage;
+
+                for (int i = 0, len = Math.min(storage.length, list.size()); i < len; ++i) {
+                    final Entity entity = storage[i];
+
+                    if (entity == null || entity == except || !entity.getBoundingBox().intersects(box)) {
+                        continue;
+                    }
+
+                    if (predicate == null || predicate.test(entity)) {
+                        into.add(entity);
+                    } // else: continue to test the ender dragon parts
+
+                    if (entity instanceof EnderDragon) {
+                        for (final EnderDragonPart part : ((EnderDragon)entity).subEntities) {
+                            if (part == except || !part.getBoundingBox().intersects(box) || !clazz.isInstance(part)) {
+                                continue;
+                            }
+
+                            if (predicate != null && !predicate.test(part)) {
+                                continue;
+                            }
+
+                            into.add(part);
+                        }
+                    }
+                }
+            }
+        }
+
+        public <T extends Entity> void getEntities(final EntityType<?> type, final AABB box, final List<? super T> into,
+                                                   final Predicate<? super T> predicate) {
+            if (this.count == 0) {
+                return;
+            }
+
+            final int minSection = this.manager.minSection;
+            final int maxSection = this.manager.maxSection;
+
+            final int min = Mth.clamp(Mth.floor(box.minY - 2.0) >> 4, minSection, maxSection);
+            final int max = Mth.clamp(Mth.floor(box.maxY + 2.0) >> 4, minSection, maxSection);
+
+            // TODO use the bitset
+
+            final BasicEntityList<Entity>[] entitiesBySection = this.entitiesBySection;
+
+            for (int section = min; section <= max; ++section) {
+                final BasicEntityList<Entity> list = entitiesBySection[section - minSection];
+
+                if (list == null) {
+                    continue;
+                }
+
+                final Entity[] storage = list.storage;
+
+                for (int i = 0, len = Math.min(storage.length, list.size()); i < len; ++i) {
+                    final Entity entity = storage[i];
+
+                    if (entity == null || (type != null && entity.getType() != type) || !entity.getBoundingBox().intersects(box)) {
+                        continue;
+                    }
+
+                    if (predicate != null && !predicate.test((T)entity)) {
+                        continue;
+                    }
+
+                    into.add((T)entity);
+                }
+            }
+        }
+    }
+}
diff --git a/src/main/java/io/papermc/paper/world/EntitySliceManager.java b/src/main/java/io/papermc/paper/world/EntitySliceManager.java
new file mode 100644
index 0000000000000000000000000000000000000000..3ba094e640d7fe7803e2bbdab8ff3beb6f50e8a0
--- /dev/null
+++ b/src/main/java/io/papermc/paper/world/EntitySliceManager.java
@@ -0,0 +1,391 @@
+package io.papermc.paper.world;
+
+import io.papermc.paper.util.CoordinateUtils;
+import io.papermc.paper.util.WorldUtil;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.util.Mth;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.entity.EntityType;
+import net.minecraft.world.phys.AABB;
+import java.util.List;
+import java.util.concurrent.locks.StampedLock;
+import java.util.function.Predicate;
+
+public final class EntitySliceManager {
+
+    protected static final int REGION_SHIFT = 5;
+    protected static final int REGION_MASK = (1 << REGION_SHIFT) - 1;
+    protected static final int REGION_SIZE = 1 << REGION_SHIFT;
+
+    public final ServerLevel world;
+
+    private final StampedLock stateLock = new StampedLock();
+    protected final Long2ObjectOpenHashMap<ChunkSlicesRegion> regions = new Long2ObjectOpenHashMap<>(64, 0.7f);
+
+    private final int minSection; // inclusive
+    private final int maxSection; // inclusive
+
+    protected final Long2ObjectOpenHashMap<ChunkHolder.FullChunkStatus> statusMap = new Long2ObjectOpenHashMap<>();
+    {
+        this.statusMap.defaultReturnValue(ChunkHolder.FullChunkStatus.INACCESSIBLE);
+    }
+
+    public EntitySliceManager(final ServerLevel world) {
+        this.world = world;
+        this.minSection = WorldUtil.getMinSection(world);
+        this.maxSection = WorldUtil.getMaxSection(world);
+    }
+
+    public void chunkStatusChange(final int x, final int z, final ChunkHolder.FullChunkStatus newStatus) {
+        if (newStatus == ChunkHolder.FullChunkStatus.INACCESSIBLE) {
+            this.statusMap.remove(CoordinateUtils.getChunkKey(x, z));
+        } else {
+            this.statusMap.put(CoordinateUtils.getChunkKey(x, z), newStatus);
+            final ChunkEntitySlices slices = this.getChunk(x, z);
+            if (slices != null) {
+                slices.updateStatus(newStatus);
+            }
+        }
+    }
+
+    public synchronized void addEntity(final Entity entity) {
+        final BlockPos pos = entity.blockPosition();
+        final int sectionX = pos.getX() >> 4;
+        final int sectionY = Mth.clamp(pos.getY() >> 4, this.minSection, this.maxSection);
+        final int sectionZ = pos.getZ() >> 4;
+        final ChunkEntitySlices slices = this.getOrCreateChunk(sectionX, sectionZ);
+        slices.addEntity(entity, sectionY);
+
+        entity.sectionX = sectionX;
+        entity.sectionY = sectionY;
+        entity.sectionZ = sectionZ;
+    }
+
+    public synchronized void removeEntity(final Entity entity) {
+        final ChunkEntitySlices slices = this.getChunk(entity.sectionX, entity.sectionZ);
+        slices.removeEntity(entity, entity.sectionY);
+        if (slices.isEmpty()) {
+            this.removeChunk(entity.sectionX, entity.sectionZ);
+        }
+    }
+
+    public void moveEntity(final Entity entity) {
+        final BlockPos newPos = entity.blockPosition();
+        final int newSectionX = newPos.getX() >> 4;
+        final int newSectionY = Mth.clamp(newPos.getY() >> 4, this.minSection, this.maxSection);
+        final int newSectionZ = newPos.getZ() >> 4;
+
+        if (newSectionX == entity.sectionX && newSectionY == entity.sectionY && newSectionZ == entity.sectionZ) {
+            return;
+        }
+
+        synchronized (this) {
+            // are we changing chunks?
+            if (newSectionX != entity.sectionX || newSectionZ != entity.sectionZ) {
+                final ChunkEntitySlices slices = this.getOrCreateChunk(newSectionX, newSectionZ);
+                final ChunkEntitySlices old = this.getChunk(entity.sectionX, entity.sectionZ);
+                synchronized (old) {
+                    old.removeEntity(entity, entity.sectionY);
+                    if (old.isEmpty()) {
+                        this.removeChunk(entity.sectionX, entity.sectionZ);
+                    }
+                }
+
+                synchronized (slices) {
+                    slices.addEntity(entity, newSectionY);
+
+                    entity.sectionX = newSectionX;
+                    entity.sectionY = newSectionY;
+                    entity.sectionZ = newSectionZ;
+                }
+            } else {
+                final ChunkEntitySlices slices = this.getChunk(newSectionX, newSectionZ);
+                // same chunk
+                synchronized (slices) {
+                    slices.removeEntity(entity, entity.sectionY);
+                    slices.addEntity(entity, newSectionY);
+                }
+                entity.sectionY = newSectionY;
+            }
+        }
+
+    }
+
+    public void getEntities(final Entity except, final AABB box, final List<Entity> into, final Predicate<? super Entity> predicate) {
+        final int minChunkX = (Mth.floor(box.minX) - 2) >> 4;
+        final int minChunkZ = (Mth.floor(box.minZ) - 2) >> 4;
+        final int maxChunkX = (Mth.floor(box.maxX) + 2) >> 4;
+        final int maxChunkZ = (Mth.floor(box.maxZ) + 2) >> 4;
+
+        final int minRegionX = minChunkX >> REGION_SHIFT;
+        final int minRegionZ = minChunkZ >> REGION_SHIFT;
+        final int maxRegionX = maxChunkX >> REGION_SHIFT;
+        final int maxRegionZ = maxChunkZ >> REGION_SHIFT;
+
+        for (int currRegionZ = minRegionZ; currRegionZ <= maxRegionZ; ++currRegionZ) {
+            final int minZ = currRegionZ == minRegionZ ? minChunkZ & REGION_MASK : 0;
+            final int maxZ = currRegionZ == maxRegionZ ? maxChunkZ & REGION_MASK : REGION_MASK;
+
+            for (int currRegionX = minRegionX; currRegionX <= maxRegionX; ++currRegionX) {
+                final ChunkSlicesRegion region = this.getRegion(currRegionX, currRegionZ);
+
+                if (region == null) {
+                    continue;
+                }
+
+                final int minX = currRegionX == minRegionX ? minChunkX & REGION_MASK : 0;
+                final int maxX = currRegionX == maxRegionX ? maxChunkX & REGION_MASK : REGION_MASK;
+
+                for (int currZ = minZ; currZ <= maxZ; ++currZ) {
+                    for (int currX = minX; currX <= maxX; ++currX) {
+                        final ChunkEntitySlices chunk = region.get(currX | (currZ << REGION_SHIFT));
+                        if (chunk == null || !chunk.status.isOrAfter(ChunkHolder.FullChunkStatus.BORDER)) {
+                            continue;
+                        }
+
+                        chunk.getEntities(except, box, into, predicate);
+                    }
+                }
+            }
+        }
+    }
+
+    public void getHardCollidingEntities(final Entity except, final AABB box, final List<Entity> into, final Predicate<? super Entity> predicate) {
+        final int minChunkX = (Mth.floor(box.minX) - 2) >> 4;
+        final int minChunkZ = (Mth.floor(box.minZ) - 2) >> 4;
+        final int maxChunkX = (Mth.floor(box.maxX) + 2) >> 4;
+        final int maxChunkZ = (Mth.floor(box.maxZ) + 2) >> 4;
+
+        final int minRegionX = minChunkX >> REGION_SHIFT;
+        final int minRegionZ = minChunkZ >> REGION_SHIFT;
+        final int maxRegionX = maxChunkX >> REGION_SHIFT;
+        final int maxRegionZ = maxChunkZ >> REGION_SHIFT;
+
+        for (int currRegionZ = minRegionZ; currRegionZ <= maxRegionZ; ++currRegionZ) {
+            final int minZ = currRegionZ == minRegionZ ? minChunkZ & REGION_MASK : 0;
+            final int maxZ = currRegionZ == maxRegionZ ? maxChunkZ & REGION_MASK : REGION_MASK;
+
+            for (int currRegionX = minRegionX; currRegionX <= maxRegionX; ++currRegionX) {
+                final ChunkSlicesRegion region = this.getRegion(currRegionX, currRegionZ);
+
+                if (region == null) {
+                    continue;
+                }
+
+                final int minX = currRegionX == minRegionX ? minChunkX & REGION_MASK : 0;
+                final int maxX = currRegionX == maxRegionX ? maxChunkX & REGION_MASK : REGION_MASK;
+
+                for (int currZ = minZ; currZ <= maxZ; ++currZ) {
+                    for (int currX = minX; currX <= maxX; ++currX) {
+                        final ChunkEntitySlices chunk = region.get(currX | (currZ << REGION_SHIFT));
+                        if (chunk == null || !chunk.status.isOrAfter(ChunkHolder.FullChunkStatus.BORDER)) {
+                            continue;
+                        }
+
+                        chunk.getHardCollidingEntities(except, box, into, predicate);
+                    }
+                }
+            }
+        }
+    }
+
+    public <T extends Entity> void getEntities(final EntityType<?> type, final AABB box, final List<? super T> into,
+                                               final Predicate<? super T> predicate) {
+        final int minChunkX = (Mth.floor(box.minX) - 2) >> 4;
+        final int minChunkZ = (Mth.floor(box.minZ) - 2) >> 4;
+        final int maxChunkX = (Mth.floor(box.maxX) + 2) >> 4;
+        final int maxChunkZ = (Mth.floor(box.maxZ) + 2) >> 4;
+
+        final int minRegionX = minChunkX >> REGION_SHIFT;
+        final int minRegionZ = minChunkZ >> REGION_SHIFT;
+        final int maxRegionX = maxChunkX >> REGION_SHIFT;
+        final int maxRegionZ = maxChunkZ >> REGION_SHIFT;
+
+        for (int currRegionZ = minRegionZ; currRegionZ <= maxRegionZ; ++currRegionZ) {
+            final int minZ = currRegionZ == minRegionZ ? minChunkZ & REGION_MASK : 0;
+            final int maxZ = currRegionZ == maxRegionZ ? maxChunkZ & REGION_MASK : REGION_MASK;
+
+            for (int currRegionX = minRegionX; currRegionX <= maxRegionX; ++currRegionX) {
+                final ChunkSlicesRegion region = this.getRegion(currRegionX, currRegionZ);
+
+                if (region == null) {
+                    continue;
+                }
+
+                final int minX = currRegionX == minRegionX ? minChunkX & REGION_MASK : 0;
+                final int maxX = currRegionX == maxRegionX ? maxChunkX & REGION_MASK : REGION_MASK;
+
+                for (int currZ = minZ; currZ <= maxZ; ++currZ) {
+                    for (int currX = minX; currX <= maxX; ++currX) {
+                        final ChunkEntitySlices chunk = region.get(currX | (currZ << REGION_SHIFT));
+                        if (chunk == null || !chunk.status.isOrAfter(ChunkHolder.FullChunkStatus.BORDER)) {
+                            continue;
+                        }
+
+                        chunk.getEntities(type, box, (List)into, (Predicate)predicate);
+                    }
+                }
+            }
+        }
+    }
+
+    public <T extends Entity> void getEntities(final Class<? extends T> clazz, final Entity except, final AABB box, final List<? super T> into,
+                                               final Predicate<? super T> predicate) {
+        final int minChunkX = (Mth.floor(box.minX) - 2) >> 4;
+        final int minChunkZ = (Mth.floor(box.minZ) - 2) >> 4;
+        final int maxChunkX = (Mth.floor(box.maxX) + 2) >> 4;
+        final int maxChunkZ = (Mth.floor(box.maxZ) + 2) >> 4;
+
+        final int minRegionX = minChunkX >> REGION_SHIFT;
+        final int minRegionZ = minChunkZ >> REGION_SHIFT;
+        final int maxRegionX = maxChunkX >> REGION_SHIFT;
+        final int maxRegionZ = maxChunkZ >> REGION_SHIFT;
+
+        for (int currRegionZ = minRegionZ; currRegionZ <= maxRegionZ; ++currRegionZ) {
+            final int minZ = currRegionZ == minRegionZ ? minChunkZ & REGION_MASK : 0;
+            final int maxZ = currRegionZ == maxRegionZ ? maxChunkZ & REGION_MASK : REGION_MASK;
+
+            for (int currRegionX = minRegionX; currRegionX <= maxRegionX; ++currRegionX) {
+                final ChunkSlicesRegion region = this.getRegion(currRegionX, currRegionZ);
+
+                if (region == null) {
+                    continue;
+                }
+
+                final int minX = currRegionX == minRegionX ? minChunkX & REGION_MASK : 0;
+                final int maxX = currRegionX == maxRegionX ? maxChunkX & REGION_MASK : REGION_MASK;
+
+                for (int currZ = minZ; currZ <= maxZ; ++currZ) {
+                    for (int currX = minX; currX <= maxX; ++currX) {
+                        final ChunkEntitySlices chunk = region.get(currX | (currZ << REGION_SHIFT));
+                        if (chunk == null || !chunk.status.isOrAfter(ChunkHolder.FullChunkStatus.BORDER)) {
+                            continue;
+                        }
+
+                        chunk.getEntities(clazz, except, box, into, predicate);
+                    }
+                }
+            }
+        }
+    }
+
+    public ChunkEntitySlices getChunk(final int chunkX, final int chunkZ) {
+        final ChunkSlicesRegion region = this.getRegion(chunkX >> REGION_SHIFT, chunkZ >> REGION_SHIFT);
+        if (region == null) {
+            return null;
+        }
+
+        return region.get((chunkX & REGION_MASK) | ((chunkZ & REGION_MASK) << REGION_SHIFT));
+    }
+
+    public ChunkEntitySlices getOrCreateChunk(final int chunkX, final int chunkZ) {
+        final ChunkSlicesRegion region = this.getRegion(chunkX >> REGION_SHIFT, chunkZ >> REGION_SHIFT);
+        ChunkEntitySlices ret;
+        if (region == null || (ret = region.get((chunkX & REGION_MASK) | ((chunkZ & REGION_MASK) << REGION_SHIFT))) == null) {
+            ret = new ChunkEntitySlices(this.world, chunkX, chunkZ, this.statusMap.get(CoordinateUtils.getChunkKey(chunkX, chunkZ)),
+                WorldUtil.getMinSection(this.world), WorldUtil.getMaxSection(this.world));
+
+            this.addChunk(chunkX, chunkZ, ret);
+
+            return ret;
+        }
+
+        return ret;
+    }
+
+    public ChunkSlicesRegion getRegion(final int regionX, final int regionZ) {
+        final long key = CoordinateUtils.getChunkKey(regionX, regionZ);
+        final long attempt = this.stateLock.tryOptimisticRead();
+        if (attempt != 0L) {
+            try {
+                final ChunkSlicesRegion ret = this.regions.get(key);
+
+                if (this.stateLock.validate(attempt)) {
+                    return ret;
+                }
+            } catch (final Error error) {
+                throw error;
+            } catch (final Throwable thr) {
+                // ignore
+            }
+        }
+
+        this.stateLock.readLock();
+        try {
+            return this.regions.get(key);
+        } finally {
+            this.stateLock.tryUnlockRead();
+        }
+    }
+
+    public synchronized void removeChunk(final int chunkX, final int chunkZ) {
+        final long key = CoordinateUtils.getChunkKey(chunkX >> REGION_SHIFT, chunkZ >> REGION_SHIFT);
+        final int relIndex = (chunkX & REGION_MASK) | ((chunkZ & REGION_MASK) << REGION_SHIFT);
+
+        final ChunkSlicesRegion region = this.regions.get(key);
+        final int remaining = region.remove(relIndex);
+
+        if (remaining == 0) {
+            this.stateLock.writeLock();
+            try {
+                this.regions.remove(key);
+            } finally {
+                this.stateLock.tryUnlockWrite();
+            }
+        }
+    }
+
+    public synchronized void addChunk(final int chunkX, final int chunkZ, final ChunkEntitySlices slices) {
+        final long key = CoordinateUtils.getChunkKey(chunkX >> REGION_SHIFT, chunkZ >> REGION_SHIFT);
+        final int relIndex = (chunkX & REGION_MASK) | ((chunkZ & REGION_MASK) << REGION_SHIFT);
+
+        ChunkSlicesRegion region = this.regions.get(key);
+        if (region != null) {
+            region.add(relIndex, slices);
+        } else {
+            region = new ChunkSlicesRegion();
+            region.add(relIndex, slices);
+            this.stateLock.writeLock();
+            try {
+                this.regions.put(key, region);
+            } finally {
+                this.stateLock.tryUnlockWrite();
+            }
+        }
+    }
+
+    public static final class ChunkSlicesRegion {
+
+        protected final ChunkEntitySlices[] slices = new ChunkEntitySlices[REGION_SIZE * REGION_SIZE];
+        protected int sliceCount;
+
+        public ChunkEntitySlices get(final int index) {
+            return this.slices[index];
+        }
+
+        public int remove(final int index) {
+            final ChunkEntitySlices slices = this.slices[index];
+            if (slices == null) {
+                throw new IllegalStateException();
+            }
+
+            this.slices[index] = null;
+
+            return --this.sliceCount;
+        }
+
+        public void add(final int index, final ChunkEntitySlices slices) {
+            final ChunkEntitySlices curr = this.slices[index];
+            if (curr != null) {
+                throw new IllegalStateException();
+            }
+
+            this.slices[index] = slices;
+
+            ++this.sliceCount;
+        }
+    }
+}
diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
index 39d96b4e3dce6d67b568b7b00456de164f6a7241..29b80d074600fa7e20b05d1fe70ac12969b954a4 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -454,7 +454,7 @@ public class ServerLevel extends Level implements WorldGenLevel {
         DataFixer datafixer = minecraftserver.getFixerUpper();
         EntityPersistentStorage<Entity> entitypersistentstorage = new EntityStorage(this, convertable_conversionsession.getDimensionPath(resourcekey).resolve("entities"), datafixer, flag2, minecraftserver);
 
-        this.entityManager = new PersistentEntitySectionManager<>(Entity.class, new ServerLevel.EntityCallbacks(), entitypersistentstorage);
+        this.entityManager = new PersistentEntitySectionManager<>(Entity.class, new ServerLevel.EntityCallbacks(), entitypersistentstorage, this.entitySliceManager); // Paper
         StructureTemplateManager structuretemplatemanager = minecraftserver.getStructureManager();
         int j = this.spigotConfig.viewDistance; // Spigot
         int k = this.spigotConfig.simulationDistance; // Spigot
diff --git a/src/main/java/net/minecraft/server/level/WorldGenRegion.java b/src/main/java/net/minecraft/server/level/WorldGenRegion.java
index 32d6e4b194c3c4eca7009059f8d185896b5ae556..51d3150e732f95be13f5f54d994dab1fa89ed3f2 100644
--- a/src/main/java/net/minecraft/server/level/WorldGenRegion.java
+++ b/src/main/java/net/minecraft/server/level/WorldGenRegion.java
@@ -498,4 +498,21 @@ public class WorldGenRegion implements WorldGenLevel {
     public long nextSubTickCount() {
         return this.subTickCount.getAndIncrement();
     }
+
+    // Paper start
+    // No-op, this class doesn't provide entity access
+    @Override
+    public List<Entity> getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate) {
+        return Collections.emptyList();
+    }
+
+    @Override
+    public void getEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into) {}
+
+    @Override
+    public void getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into) {}
+
+    @Override
+    public <T> void getEntitiesByClass(Class<? extends T> clazz, Entity except, AABB box, List<? super T> into, Predicate<? super T> predicate) {}
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index 6f3147713b5bec3b2771e1ec52917fd4aee681bc..9567822f314cd3978ed63bb867e57b610d76228e 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -490,6 +490,56 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
     }
     // Paper end - make end portalling safe
 
+    // Paper start
+    /**
+     * Overriding this field will cause memory leaks.
+     */
+    private final boolean hardCollides;
+
+    private static final java.util.Map<Class<? extends Entity>, Boolean> cachedOverrides = java.util.Collections.synchronizedMap(new java.util.WeakHashMap<>());
+    {
+        /* // Goodbye, broken on reobf...
+        Boolean hardCollides = cachedOverrides.get(this.getClass());
+        if (hardCollides == null) {
+            try {
+                java.lang.reflect.Method getHardCollisionBoxEntityMethod = Entity.class.getMethod("canCollideWith", Entity.class);
+                java.lang.reflect.Method hasHardCollisionBoxMethod = Entity.class.getMethod("canBeCollidedWith");
+                if (!this.getClass().getMethod(hasHardCollisionBoxMethod.getName(), hasHardCollisionBoxMethod.getParameterTypes()).equals(hasHardCollisionBoxMethod)
+                        || !this.getClass().getMethod(getHardCollisionBoxEntityMethod.getName(), getHardCollisionBoxEntityMethod.getParameterTypes()).equals(getHardCollisionBoxEntityMethod)) {
+                    hardCollides = Boolean.TRUE;
+                } else {
+                    hardCollides = Boolean.FALSE;
+                }
+                cachedOverrides.put(this.getClass(), hardCollides);
+            }
+            catch (ThreadDeath thr) { throw thr; }
+            catch (Throwable thr) {
+                // shouldn't happen, just explode
+                throw new RuntimeException(thr);
+            }
+        } */
+        this.hardCollides = this instanceof Boat
+            || this instanceof net.minecraft.world.entity.monster.Shulker
+            || this instanceof net.minecraft.world.entity.vehicle.AbstractMinecart
+            || this.shouldHardCollide();
+    }
+
+    // plugins can override
+    protected boolean shouldHardCollide() {
+        return false;
+    }
+
+    public final boolean hardCollides() {
+        return this.hardCollides;
+    }
+
+    public net.minecraft.server.level.ChunkHolder.FullChunkStatus chunkStatus;
+
+    public int sectionX = Integer.MIN_VALUE;
+    public int sectionY = Integer.MIN_VALUE;
+    public int sectionZ = Integer.MIN_VALUE;
+    // Paper end
+
     public Entity(EntityType<?> type, Level world) {
         this.id = Entity.ENTITY_COUNTER.incrementAndGet();
         this.passengers = ImmutableList.of();
@@ -2358,11 +2408,11 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
         return InteractionResult.PASS;
     }
 
-    public boolean canCollideWith(Entity other) {
+    public boolean canCollideWith(Entity other) { // Paper - diff on change, hard colliding entities override this - TODO CHECK ON UPDATE - AbstractMinecart/Boat override
         return other.canBeCollidedWith() && !this.isPassengerOfSameVehicle(other);
     }
 
-    public boolean canBeCollidedWith() {
+    public boolean canBeCollidedWith() { // Paper - diff on change, hard colliding entities override this TODO CHECK ON UPDATE - Boat/Shulker override
         return false;
     }
 
diff --git a/src/main/java/net/minecraft/world/level/EntityGetter.java b/src/main/java/net/minecraft/world/level/EntityGetter.java
index 1a3be6f0570c7c746eafa36544debe90d7629432..c0817ef8927f00e2fd3fbf3289f8041fcb494049 100644
--- a/src/main/java/net/minecraft/world/level/EntityGetter.java
+++ b/src/main/java/net/minecraft/world/level/EntityGetter.java
@@ -18,6 +18,18 @@ import net.minecraft.world.phys.shapes.Shapes;
 import net.minecraft.world.phys.shapes.VoxelShape;
 
 public interface EntityGetter {
+
+    // Paper start
+    List<Entity> getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate);
+
+    void getEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into);
+
+    void getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into);
+
+    <T> void getEntitiesByClass(Class<? extends T> clazz, Entity except, final AABB box, List<? super T> into,
+                                Predicate<? super T> predicate);
+    // Paper end
+
     List<Entity> getEntities(@Nullable Entity except, AABB box, Predicate<? super Entity> predicate);
 
     <T extends Entity> List<T> getEntities(EntityTypeTest<Entity, T> filter, AABB box, Predicate<? super T> predicate);
diff --git a/src/main/java/net/minecraft/world/level/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index 2a4e6c6f732d9cd2567352b7fca2c284b0bb9c1b..4f484e71c93a5243d242e116e2f204ead407f598 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -293,6 +293,7 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
         this.entityLimiter = new org.spigotmc.TickLimiter(spigotConfig.entityMaxTickTime);
         this.tileLimiter = new org.spigotmc.TickLimiter(spigotConfig.tileMaxTickTime);
         this.chunkPacketBlockController = this.paperConfig().anticheat.antiXray.enabled ? new com.destroystokyo.paper.antixray.ChunkPacketBlockControllerAntiXray(this, executor) : com.destroystokyo.paper.antixray.ChunkPacketBlockController.NO_OPERATION_INSTANCE; // Paper - Anti-Xray
+        this.entitySliceManager = new io.papermc.paper.world.EntitySliceManager((ServerLevel)this); // Paper
     }
 
     // Paper start
@@ -967,26 +968,7 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
     public List<Entity> getEntities(@Nullable Entity except, AABB box, Predicate<? super Entity> predicate) {
         this.getProfiler().incrementCounter("getEntities");
         List<Entity> list = Lists.newArrayList();
-
-        this.getEntities().get(box, (entity1) -> {
-            if (entity1 != except && predicate.test(entity1)) {
-                list.add(entity1);
-            }
-
-            if (entity1 instanceof EnderDragon) {
-                EnderDragonPart[] aentitycomplexpart = ((EnderDragon) entity1).getSubEntities();
-                int i = aentitycomplexpart.length;
-
-                for (int j = 0; j < i; ++j) {
-                    EnderDragonPart entitycomplexpart = aentitycomplexpart[j];
-
-                    if (entity1 != except && predicate.test(entitycomplexpart)) {
-                        list.add(entitycomplexpart);
-                    }
-                }
-            }
-
-        }, predicate == net.minecraft.world.entity.EntitySelector.CONTAINER_ENTITY_SELECTOR); // Paper
+        this.entitySliceManager.getEntities(except, box, list, predicate); // Paper - optimise this call
         return list;
     }
 
@@ -995,27 +977,22 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
         this.getProfiler().incrementCounter("getEntities");
         List<T> list = Lists.newArrayList();
 
-        this.getEntities().get(filter, box, (entity) -> {
-            if (predicate.test(entity)) {
-                list.add(entity);
-            }
-
-            if (entity instanceof EnderDragon) {
-                EnderDragon entityenderdragon = (EnderDragon) entity;
-                EnderDragonPart[] aentitycomplexpart = entityenderdragon.getSubEntities();
-                int i = aentitycomplexpart.length;
-
-                for (int j = 0; j < i; ++j) {
-                    EnderDragonPart entitycomplexpart = aentitycomplexpart[j];
-                    T t0 = filter.tryCast(entitycomplexpart); // CraftBukkit - decompile error
-
-                    if (t0 != null && predicate.test(t0)) {
-                        list.add(t0);
-                    }
-                }
+        // Paper start - optimise this call
+        if (filter instanceof net.minecraft.world.entity.EntityType) {
+            this.entitySliceManager.getEntities((net.minecraft.world.entity.EntityType)filter, box, list, predicate);
+        } else {
+            Predicate<? super T> test = (obj) -> {
+                return filter.tryCast(obj) != null;
+            };
+            predicate = predicate == null ? test : test.and((Predicate)predicate);
+            Class base;
+            if (filter == null || (base = filter.getBaseClass()) == null || base == Entity.class) {
+                this.entitySliceManager.getEntities((Entity) null, box, (List)list, (Predicate)predicate);
+            } else {
+                this.entitySliceManager.getEntities(base, null, box, (List)list, (Predicate)predicate); // Paper - optimise this call
             }
-
-        });
+        }
+        // Paper end - optimise this call
         return list;
     }
 
@@ -1342,4 +1319,46 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
     public long nextSubTickCount() {
         return (long) (this.subTickCount++);
     }
+
+    // Paper start
+    protected final io.papermc.paper.world.EntitySliceManager entitySliceManager;
+
+    public org.bukkit.entity.Entity[] getChunkEntities(int chunkX, int chunkZ) {
+        io.papermc.paper.world.ChunkEntitySlices slices = this.entitySliceManager.getChunk(chunkX, chunkZ);
+        if (slices == null) {
+            return new org.bukkit.entity.Entity[0];
+        }
+        return slices.getChunkEntities();
+    }
+
+    @Override
+    public List<Entity> getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate) {
+        List<Entity> ret = new java.util.ArrayList<>();
+        this.entitySliceManager.getEntities(except, box, ret, predicate);
+        return ret;
+    }
+
+    @Override
+    public void getEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into) {
+        this.entitySliceManager.getEntities(except, box, into, predicate);
+    }
+
+    @Override
+    public void getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into) {
+        this.entitySliceManager.getHardCollidingEntities(except, box, into, predicate);
+    }
+
+    @Override
+    public <T> void getEntitiesByClass(Class<? extends T> clazz, Entity except, final AABB box, List<? super T> into,
+                                       Predicate<? super T> predicate) {
+        this.entitySliceManager.getEntities((Class)clazz, except, box, (List)into, (Predicate)predicate);
+    }
+
+    @Override
+    public <T extends Entity> List<T> getEntitiesOfClass(Class<T> entityClass, AABB box, Predicate<? super T> predicate) {
+        List<T> ret = new java.util.ArrayList<>();
+        this.entitySliceManager.getEntities(entityClass, null, box, ret, predicate);
+        return ret;
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java b/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java
index a1a52669c19af22e3b5267d43584cb00d1646453..f635b610e68d129aa0ae60c54b83da6943946436 100644
--- a/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java
+++ b/src/main/java/net/minecraft/world/level/entity/PersistentEntitySectionManager.java
@@ -49,8 +49,10 @@ public class PersistentEntitySectionManager<T extends EntityAccess> implements A
     private final Long2ObjectMap<PersistentEntitySectionManager.ChunkLoadStatus> chunkLoadStatuses = new Long2ObjectOpenHashMap();
     private final LongSet chunksToUnload = new LongOpenHashSet();
     private final Queue<ChunkEntities<T>> loadingInbox = Queues.newConcurrentLinkedQueue();
+    public final io.papermc.paper.world.EntitySliceManager entitySliceManager; // Paper
 
-    public PersistentEntitySectionManager(Class<T> entityClass, LevelCallback<T> handler, EntityPersistentStorage<T> dataAccess) {
+    public PersistentEntitySectionManager(Class<T> entityClass, LevelCallback<T> handler, EntityPersistentStorage<T> dataAccess, io.papermc.paper.world.EntitySliceManager entitySliceManager) { // Paper
+        this.entitySliceManager = entitySliceManager; // Paper
         this.sectionStorage = new EntitySectionStorage<>(entityClass, this.chunkVisibility);
         this.chunkVisibility.defaultReturnValue(Visibility.HIDDEN);
         this.chunkLoadStatuses.defaultReturnValue(PersistentEntitySectionManager.ChunkLoadStatus.FRESH);
@@ -124,6 +126,7 @@ public class PersistentEntitySectionManager<T extends EntityAccess> implements A
             EntitySection<T> entitysection = this.sectionStorage.getOrCreateSection(i);
 
             entitysection.add(entity);
+            this.entitySliceManager.addEntity((Entity)entity); // Paper
             entity.setLevelCallback(new PersistentEntitySectionManager.Callback(entity, i, entitysection));
             if (!existing) {
                 this.callbacks.onCreated(entity);
@@ -181,6 +184,7 @@ public class PersistentEntitySectionManager<T extends EntityAccess> implements A
         io.papermc.paper.util.TickThread.ensureTickThread("Asynchronous chunk ticking status update"); // Paper
         Visibility visibility = Visibility.fromFullChunkStatus(levelType);
 
+        this.entitySliceManager.chunkStatusChange(chunkPos.x, chunkPos.z, levelType); // Paper
         this.updateChunkStatus(chunkPos, visibility);
     }
 
@@ -467,6 +471,7 @@ public class PersistentEntitySectionManager<T extends EntityAccess> implements A
             long i = SectionPos.asLong(blockposition);
 
             if (i != this.currentSectionKey) {
+                PersistentEntitySectionManager.this.entitySliceManager.moveEntity((Entity)this.entity); // Paper
                 Visibility visibility = this.currentSection.getStatus();
 
                 if (!this.currentSection.remove(this.entity)) {
@@ -524,6 +529,7 @@ public class PersistentEntitySectionManager<T extends EntityAccess> implements A
             if (!this.currentSection.remove(this.entity)) {
                 PersistentEntitySectionManager.LOGGER.warn("Entity {} wasn't found in section {} (destroying due to {})", new Object[]{this.entity, SectionPos.of(this.currentSectionKey), reason});
             }
+            PersistentEntitySectionManager.this.entitySliceManager.removeEntity((Entity)this.entity); // Paper
 
             Visibility visibility = PersistentEntitySectionManager.getEffectiveStatus(this.entity, this.currentSection.getStatus());
 
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftChunk.java b/src/main/java/org/bukkit/craftbukkit/CraftChunk.java
index 518dfbb7dbd4221937636cf46d27109de6f431a4..e86b3ee5c8225d9f789cf426cc1418fde0fa12f0 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftChunk.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftChunk.java
@@ -134,9 +134,7 @@ public class CraftChunk implements Chunk {
         long pair = ChunkPos.asLong(x, z);
 
         if (entityManager.areEntitiesLoaded(pair)) {
-            return entityManager.getEntities(new ChunkPos(this.x, this.z)).stream()
-                    .map(net.minecraft.world.entity.Entity::getBukkitEntity)
-                    .filter(Objects::nonNull).toArray(Entity[]::new);
+            return getCraftWorld().getHandle().getChunkEntities(this.x, this.z); // Paper - optimise this
         }
 
         entityManager.ensureChunkQueuedForLoad(pair); // Start entity loading
@@ -172,9 +170,7 @@ public class CraftChunk implements Chunk {
             }
         }
 
-        return entityManager.getEntities(new ChunkPos(this.x, this.z)).stream()
-                .map(net.minecraft.world.entity.Entity::getBukkitEntity)
-                .filter(Objects::nonNull).toArray(Entity[]::new);
+        return getCraftWorld().getHandle().getChunkEntities(this.x, this.z); // Paper - optimise this
     }
 
     @Override
diff --git a/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java b/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java
index 3bedc22c253c3632b5624c05e78ed3671e5d30ce..fbd82b6be6604bf854e01ed5718e4e072f42b265 100644
--- a/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java
+++ b/src/main/java/org/bukkit/craftbukkit/util/DummyGeneratorAccess.java
@@ -254,4 +254,20 @@ public class DummyGeneratorAccess implements WorldGenLevel {
     public boolean destroyBlock(BlockPos pos, boolean drop, Entity breakingEntity, int maxUpdateDepth) {
         return false; // SPIGOT-6515
     }
+
+    // Paper start
+    @Override
+    public List<Entity> getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate) {
+        return java.util.Collections.emptyList();
+    }
+
+    @Override
+    public void getEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into) {}
+
+    @Override
+    public void getHardCollidingEntities(Entity except, AABB box, Predicate<? super Entity> predicate, List<Entity> into) {}
+
+    @Override
+    public <T> void getEntitiesByClass(Class<? extends T> clazz, Entity except, AABB box, List<? super T> into, Predicate<? super T> predicate) {}
+    // Paper end
 }
diff --git a/src/main/java/org/spigotmc/ActivationRange.java b/src/main/java/org/spigotmc/ActivationRange.java
index 0508f43ad396679d3372ae4caf029086a1524109..b1ed97618d08d7691d24f89e9e9b0ed0f2bddd09 100644
--- a/src/main/java/org/spigotmc/ActivationRange.java
+++ b/src/main/java/org/spigotmc/ActivationRange.java
@@ -211,7 +211,13 @@ public class ActivationRange
             ActivationType.VILLAGER.boundingBox = player.getBoundingBox().inflate( villagerActivationRange, worldHeight, villagerActivationRange );
             // Paper end
 
-            world.getEntities().get(maxBB, ActivationRange::activateEntity);
+            // Paper start
+            java.util.List<Entity> entities = world.getEntities((Entity)null, maxBB, null);
+            for (int i = 0; i < entities.size(); i++) {
+                Entity entity = entities.get(i);
+                ActivationRange.activateEntity(entity);
+            }
+            // Paper end
         }
         MinecraftTimings.entityActivationCheckTimer.stopTiming();
     }