From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Fri, 14 Feb 2020 01:24:39 -0800
Subject: [PATCH] Optimise TickListServer by rewriting it

In my profiling TickListServer showed up as
~10% for saving chunks and ~5% for the scheduling
of items on a server with ~90 players at
view distance = 5. Most of the performance
loss is unneccessary.

TickListServer has numerous performance issues:
 1. Handling scheduled items is O(nlogn)
 2. Getting scheduled items for a chunk is O(n),
    with n being the the number of scheduled items
    for all chunks (hits saving very hard)
 3. Checking if an item is scheduled for the current tick is O(n),
    with n being the number of items scheduled for current tick
 4. Items not in ticking chunks are churned in the scheduler

The biggest issues are 4 & 2.

We solve 1 by splitting up scheduled items into short and long scheduled,
where we expect the vast majority of our entries to be in the short scheduled
set. Handling short scheduled items is O(n) due to how the comparison
process is reduced to mapping. See TickListServerInterval. However,
this isn't memory-efficient - which is why long scheduled exists.
Long scheduled is handled the same as TickListServer.

2 is solved by mapping what entries are in what chunks.

3 is solved by mapping what blocks have what scheduled for them.

4 is solved by moving the items that are not in ticking chunks
into a map of entries for that chunk. Once the chunk is moved
to ticking, the items are re-scheduled.

This patch has also added two flags to debug excessive tick delays:
-Dpaper.ticklist-warn-on-excessive-delay=true (false by default)
and -Dpaper.ticklist-excessive-delay-threshold=ticks which
sets the excessive tick delay to the specified ticks (defaults to
60 * 20 ticks, aka 60 seconds)

diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
index 0fcabd12408a8209da5cb3332e217f98983aec02..9b1845024d16a7875ba3406da92efb003f58f8cb 100644
--- a/src/main/java/com/destroystokyo/paper/PaperConfig.java
+++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
@@ -349,6 +349,13 @@ public class PaperConfig {
         maxBookTotalSizeMultiplier = getDouble("settings.book-size.total-multiplier", maxBookTotalSizeMultiplier);
     }
 
+    public static boolean useOptimizedTickList = true;
+    private static void useOptimizedTickList() {
+        if (config.contains("settings.use-optimized-ticklist")) { // don't add default, hopefully temporary config
+            useOptimizedTickList = config.getBoolean("settings.use-optimized-ticklist");
+        }
+    }
+
     public static boolean asyncChunks = false;
     private static void asyncChunks() {
         ConfigurationSection section;
diff --git a/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java b/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
new file mode 100644
index 0000000000000000000000000000000000000000..e7624948ea4aa1a07d84ed3d295cfe2dd354fd14
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/server/ticklist/PaperTickList.java
@@ -0,0 +1,628 @@
+package com.destroystokyo.paper.server.ticklist;
+
+import net.minecraft.server.MCUtil;
+import net.minecraft.server.MinecraftServer;
+import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ObjectRBTreeSet;
+import net.minecraft.server.BlockPosition;
+import net.minecraft.server.ChunkCoordIntPair;
+import net.minecraft.server.ChunkProviderServer;
+import net.minecraft.server.CrashReport;
+import net.minecraft.server.CrashReportSystemDetails;
+import net.minecraft.server.IBlockData;
+import net.minecraft.server.MinecraftKey;
+import net.minecraft.server.NBTTagList;
+import net.minecraft.server.NextTickListEntry;
+import net.minecraft.server.ReportedException;
+import net.minecraft.server.StructureBoundingBox;
+import net.minecraft.server.TickListPriority;
+import net.minecraft.server.TickListServer;
+import net.minecraft.server.WorldServer;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+public final class PaperTickList<T> extends TickListServer<T> { // extend to avoid breaking ABI
+
+    // in the order the state is expected to change (mostly)
+    public static final int STATE_UNSCHEDULED    = 1 << 0;
+    public static final int STATE_SCHEDULED      = 1 << 1; // scheduled for some tick
+    public static final int STATE_PENDING_TICK   = 1 << 2; // for this tick
+    public static final int STATE_TICKING        = 1 << 3;
+    public static final int STATE_TICKED         = 1 << 4; // after this, it gets thrown back to unscheduled
+    public static final int STATE_CANCELLED_TICK = 1 << 5; // still gets moved to unscheduled after tick
+
+    private static final int SHORT_SCHEDULE_TICK_THRESHOLD = 20 * 20 + 1; // 20 seconds
+
+    private final WorldServer world;
+    private final Predicate<T> excludeFromScheduling;
+    private final Function<T, MinecraftKey> getMinecraftKeyFrom;
+    //private final Function<MinecraftKey, T> getObjectFronMinecraftKey;
+    private final Consumer<NextTickListEntry<T>> tickFunction;
+
+    private final co.aikar.timings.Timing timingCleanup; // Paper
+    private final co.aikar.timings.Timing timingTicking; // Paper
+    private final co.aikar.timings.Timing timingFinished;
+
+    // note: remove ops / add ops suck on fastutil, a chained hashtable implementation would work better, but Long...
+    // try to alleviate with a very small load factor
+    private final Long2ObjectOpenHashMap<ArrayList<NextTickListEntry<T>>> entriesByBlock = new Long2ObjectOpenHashMap<>(1024, 0.25f);
+    private final Long2ObjectOpenHashMap<ObjectRBTreeSet<NextTickListEntry<T>>> entriesByChunk = new Long2ObjectOpenHashMap<>(1024, 0.25f);
+    private final Long2ObjectOpenHashMap<ArrayList<NextTickListEntry<T>>> pendingChunkTickLoad = new Long2ObjectOpenHashMap<>(1024, 0.5f);
+
+    // fastutil has O(1) first/last while TreeMap/TreeSet are log(n)
+    private final ObjectRBTreeSet<NextTickListEntry<T>> longScheduled = new ObjectRBTreeSet<>(TickListServerInterval.ENTRY_COMPARATOR);
+
+    private final ArrayDeque<NextTickListEntry<T>> toTickThisTick = new ArrayDeque<>();
+
+    private final TickListServerInterval<T>[] shortScheduled = new TickListServerInterval[SHORT_SCHEDULE_TICK_THRESHOLD];
+    {
+        for (int i = 0, len = this.shortScheduled.length; i < len; ++i) {
+            this.shortScheduled[i] = new TickListServerInterval<>();
+        }
+    }
+    private int shortScheduledIndex;
+
+    private long currentTick;
+
+    private static final boolean WARN_ON_EXCESSIVE_DELAY = Boolean.getBoolean("paper.ticklist-warn-on-excessive-delay");
+    private static final long EXCESSIVE_DELAY_THRESHOLD = Long.getLong("paper.ticklist-excessive-delay-threshold", 60 * 20).longValue(); // 1 min dfl
+
+    // assume index < length
+    private static int getWrappedIndex(final int start, final int length, final int index) {
+        final int next = start + index;
+        return next < length ? next : next - length;
+    }
+
+    private static int getNextIndex(final int curr, final int length) {
+        final int next = curr + 1;
+        return next < length ? next : 0;
+    }
+
+    public PaperTickList(final WorldServer world, final Predicate<T> excludeFromScheduling, final Function<T, MinecraftKey> getMinecraftKeyFrom,
+                         final Consumer<NextTickListEntry<T>> tickFunction, final String timingsType) {
+        super(world, excludeFromScheduling, getMinecraftKeyFrom, tickFunction, timingsType);
+        this.world = world;
+        this.excludeFromScheduling = excludeFromScheduling;
+        this.getMinecraftKeyFrom = getMinecraftKeyFrom;
+        this.tickFunction = tickFunction;
+        this.timingCleanup = co.aikar.timings.WorldTimingsHandler.getTickList(world, timingsType + " - Cleanup"); // Paper
+        this.timingTicking = co.aikar.timings.WorldTimingsHandler.getTickList(world, timingsType + " - Ticking"); // Paper
+        this.timingFinished = co.aikar.timings.WorldTimingsHandler.getTickList(world, timingsType + " - Finish");
+        this.currentTick = this.world.getTime();
+    }
+
+    private void queueEntryForTick(final NextTickListEntry<T> entry, final ChunkProviderServer chunkProvider) {
+        if (entry.tickState == STATE_SCHEDULED) {
+            if (chunkProvider.isTickingReadyMainThread(entry.getPosition())) {
+                this.toTickThisTick.add(entry);
+                entry.tickState = STATE_PENDING_TICK;
+            } else {
+                // we dump them to a map to avoid constantly re-scheduling them
+                this.addToNotTickingReady(entry);
+            }
+        }
+    }
+
+    private void addToNotTickingReady(final NextTickListEntry<T> entry) {
+        this.pendingChunkTickLoad.computeIfAbsent(MCUtil.getCoordinateKey(entry.getPosition()), (long keyInMap) -> {
+            return new ArrayList<>();
+        }).add(entry);
+    }
+
+    private void addToSchedule(final NextTickListEntry<T> entry) {
+        long delay = entry.getTargetTick() - (this.currentTick + 1);
+        if (delay < SHORT_SCHEDULE_TICK_THRESHOLD) {
+            if (delay < 0) {
+                // longScheduled orders by tick time, short scheduled does not
+                this.longScheduled.add(entry);
+            } else {
+                this.shortScheduled[getWrappedIndex(this.shortScheduledIndex, SHORT_SCHEDULE_TICK_THRESHOLD, (int)delay)].addEntryLast(entry);
+            }
+        } else {
+            this.longScheduled.add(entry);
+        }
+    }
+
+    private void removeEntry(final NextTickListEntry<T> entry) {
+        entry.tickState = STATE_CANCELLED_TICK;
+        // short/long scheduled will skip the entry
+
+        final BlockPosition pos = entry.getPosition();
+        final long blockKey = MCUtil.getBlockKey(pos);
+
+        final ArrayList<NextTickListEntry<T>> currentEntries = this.entriesByBlock.get(blockKey);
+
+        if (currentEntries.size() == 1) {
+            // it should contain our entry
+            this.entriesByBlock.remove(blockKey);
+        } else {
+            // it's more likely that this entry is at the start of the list than the end
+            for (int i = 0, len = currentEntries.size(); i < len; ++i) {
+                final NextTickListEntry<T> currentEntry = currentEntries.get(i);
+                if (currentEntry == entry) {
+                    currentEntries.remove(i);
+                    break;
+                }
+            }
+        }
+
+        final long chunkKey = MCUtil.getCoordinateKey(entry.getPosition());
+
+        ObjectRBTreeSet<NextTickListEntry<T>> set = this.entriesByChunk.get(chunkKey);
+
+        set.remove(entry);
+
+        if (set.isEmpty()) {
+            this.entriesByChunk.remove(chunkKey);
+        }
+
+        ArrayList<NextTickListEntry<T>> pendingTickingLoad = this.pendingChunkTickLoad.get(chunkKey);
+
+        if (pendingTickingLoad != null) {
+            for (int i = 0, len = pendingTickingLoad.size(); i < len; ++i) {
+                if (pendingTickingLoad.get(i) == entry) {
+                    pendingTickingLoad.remove(i);
+                    break;
+                }
+            }
+
+            if (pendingTickingLoad.isEmpty()) {
+                this.pendingChunkTickLoad.remove(chunkKey);
+            }
+        }
+
+        long delay = entry.getTargetTick() - (this.currentTick + 1);
+        if (delay >= SHORT_SCHEDULE_TICK_THRESHOLD) {
+            this.longScheduled.remove(entry);
+        }
+    }
+
+    public void onChunkSetTicking(final int chunkX, final int chunkZ) {
+        final ArrayList<NextTickListEntry<T>> pending = this.pendingChunkTickLoad.remove(MCUtil.getCoordinateKey(chunkX, chunkZ));
+        if (pending == null) {
+            return;
+        }
+
+        for (int i = 0, size = pending.size(); i < size; ++i) {
+            final NextTickListEntry<T> entry = pending.get(i);
+            // already in all the relevant reference maps, just need to add to longScheduled or shortScheduled
+            this.addToSchedule(entry);
+        }
+    }
+
+    private void prepare() {
+        final long currentTick = this.currentTick;
+
+        final ChunkProviderServer chunkProvider = this.world.getChunkProvider();
+
+        // here we setup what's going to tick
+
+        // we don't remove items from shortScheduled (but do from longScheduled) because they're cleared at the end of
+        // this tick
+        if (this.longScheduled.isEmpty() || this.longScheduled.first().getTargetTick() > currentTick) {
+            // nothing in longScheduled to worry about
+            final TickListServerInterval<T> interval = this.shortScheduled[this.shortScheduledIndex];
+            for (int i = 0, len = interval.byPriority.length; i < len; ++i) {
+                for (final Iterator<NextTickListEntry<T>> iterator = interval.byPriority[i].iterator(); iterator.hasNext();) {
+                    this.queueEntryForTick(iterator.next(), chunkProvider);
+                }
+            }
+        } else {
+            final TickListServerInterval<T> interval = this.shortScheduled[this.shortScheduledIndex];
+
+            // combine interval and longScheduled, keeping order
+            final Comparator<NextTickListEntry<T>> comparator = (Comparator)TickListServerInterval.ENTRY_COMPARATOR;
+            final Iterator<NextTickListEntry<T>> longScheduledIterator = this.longScheduled.iterator();
+            NextTickListEntry<T> longCurrent = longScheduledIterator.next();
+
+            for (int i = 0, len = interval.byPriority.length; i < len; ++i) {
+                for (final Iterator<NextTickListEntry<T>> iterator = interval.byPriority[i].iterator(); iterator.hasNext();) {
+                    final NextTickListEntry<T> shortCurrent = iterator.next();
+                    if (longCurrent != null) {
+                        // drain longCurrent until we can add shortCurrent
+                        while (comparator.compare(longCurrent, shortCurrent) <= 0) {
+                            this.queueEntryForTick(longCurrent, chunkProvider);
+                            longScheduledIterator.remove();
+                            if (longScheduledIterator.hasNext()) {
+                                longCurrent = longScheduledIterator.next();
+                                if (longCurrent.getTargetTick() > currentTick) {
+                                    longCurrent = null;
+                                    break;
+                                }
+                            } else {
+                                longCurrent = null;
+                                break;
+                            }
+                        }
+                    }
+                    this.queueEntryForTick(shortCurrent, chunkProvider);
+                }
+            }
+
+            // add remaining from long scheduled
+            for (;;) {
+                if (longCurrent == null || longCurrent.getTargetTick() > currentTick) {
+                    break;
+                }
+                longScheduledIterator.remove();
+                this.queueEntryForTick(longCurrent, chunkProvider);
+
+                if (longScheduledIterator.hasNext()) {
+                    longCurrent = longScheduledIterator.next();
+                } else {
+                    break;
+                }
+            }
+        }
+    }
+
+    private boolean warnedAboutDesync;
+
+    @Override
+    protected void nextTick() {
+        ++this.currentTick;
+        if (this.currentTick != this.world.getTime()) {
+            if (!this.warnedAboutDesync) {
+                this.warnedAboutDesync = true;
+                MinecraftServer.LOGGER.error("World tick desync detected! Expected " + this.currentTick + " ticks, but got " + this.world.getTime() + " ticks for world '" + this.world.getWorld().getName() + "'", new Throwable());
+                MinecraftServer.LOGGER.error("Preventing redstone from breaking by refusing to accept new tick time");
+            }
+        }
+    }
+
+    @Override
+    public void tick() {
+        final ChunkProviderServer chunkProvider = this.world.getChunkProvider();
+
+        this.world.getMethodProfiler().enter("cleaning");
+        this.timingCleanup.startTiming();
+
+        this.prepare();
+
+        // this must be done here in case something schedules in the tick code
+        this.shortScheduled[this.shortScheduledIndex].clear();
+        this.shortScheduledIndex = getNextIndex(this.shortScheduledIndex, SHORT_SCHEDULE_TICK_THRESHOLD);
+
+        this.timingCleanup.stopTiming();
+        this.world.getMethodProfiler().exitEnter("ticking");
+        this.timingTicking.startTiming();
+
+        for (final NextTickListEntry<T> toTick : this.toTickThisTick) {
+            if (toTick.tickState != STATE_PENDING_TICK) {
+                // onTickEnd gets called at end of tick
+                continue;
+            }
+            try {
+                if (chunkProvider.isTickingReadyMainThread(toTick.getPosition())) {
+                    toTick.tickState = STATE_TICKING;
+                    this.tickFunction.accept(toTick);
+                    if (toTick.tickState == STATE_TICKING) {
+                        toTick.tickState = STATE_TICKED;
+                    } // else it's STATE_CANCELLED_TICK
+                } else {
+                    // re-schedule eventually
+                    toTick.tickState = STATE_SCHEDULED;
+                    this.addToNotTickingReady(toTick);
+                }
+            } catch (final Throwable thr) {
+                // start copy from TickListServer // TODO check on update
+                CrashReport crashreport = CrashReport.a(thr, "Exception while ticking");
+                CrashReportSystemDetails crashreportsystemdetails = crashreport.a("Block being ticked");
+
+                CrashReportSystemDetails.a(crashreportsystemdetails, toTick.getPosition(), (IBlockData) null);
+                throw new ReportedException(crashreport);
+                // end copy from TickListServer
+            }
+        }
+
+        this.timingTicking.stopTiming();
+        this.world.getMethodProfiler().exit();
+        this.timingFinished.startTiming();
+
+        // finished ticking, actual cleanup time
+        for (int i = 0, len = this.toTickThisTick.size(); i < len; ++i) {
+            final NextTickListEntry<T> entry = this.toTickThisTick.poll();
+            if (entry.tickState != STATE_SCHEDULED) {
+                // some entries get re-scheduled due to their chunk not being loaded/at correct status, so do not
+                // call onTickEnd for them
+                this.onTickEnd(entry);
+            }
+        }
+
+        this.timingFinished.stopTiming();
+    }
+
+    private void onTickEnd(final NextTickListEntry<T> entry) {
+        if (entry.tickState == STATE_CANCELLED_TICK) {
+            return;
+        }
+        entry.tickState = STATE_UNSCHEDULED;
+
+        final BlockPosition pos = entry.getPosition();
+        final long blockKey = MCUtil.getBlockKey(pos);
+
+        final ArrayList<NextTickListEntry<T>> currentEntries = this.entriesByBlock.get(blockKey);
+
+        if (currentEntries.size() == 1) {
+            // it should contain our entry
+            this.entriesByBlock.remove(blockKey);
+        } else {
+            // it's more likely that this entry is at the start of the list than the end
+            for (int i = 0, len = currentEntries.size(); i < len; ++i) {
+                final NextTickListEntry<T> currentEntry = currentEntries.get(i);
+                if (currentEntry == entry) {
+                    currentEntries.remove(i);
+                    break;
+                }
+            }
+        }
+
+        final long chunkKey = MCUtil.getCoordinateKey(entry.getPosition());
+
+        ObjectRBTreeSet<NextTickListEntry<T>> set = this.entriesByChunk.get(chunkKey);
+
+        set.remove(entry);
+
+        if (set.isEmpty()) {
+            this.entriesByChunk.remove(chunkKey);
+        }
+
+        // already removed from longScheduled or shortScheduled
+    }
+
+    @Override
+    public boolean isPendingTickThisTick(final BlockPosition blockposition, final T data) {
+        final ArrayList<NextTickListEntry<T>> entries = this.entriesByBlock.get(MCUtil.getBlockKey(blockposition));
+
+        if (entries == null) {
+            return false;
+        }
+
+        for (int i = 0, size = entries.size(); i < size; ++i) {
+            final NextTickListEntry<T> entry = entries.get(i);
+            if (entry.getData() == data && entry.tickState == STATE_PENDING_TICK) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    @Override
+    public boolean isScheduledForTick(final BlockPosition blockposition, final T data) {
+        final ArrayList<NextTickListEntry<T>> entries = this.entriesByBlock.get(MCUtil.getBlockKey(blockposition));
+
+        if (entries == null) {
+            return false;
+        }
+
+        for (int i = 0, size = entries.size(); i < size; ++i) {
+            final NextTickListEntry<T> entry = entries.get(i);
+            if (entry.getData() == data && entry.tickState == STATE_SCHEDULED) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    @Override
+    public void schedule(BlockPosition blockPosition, T t, int i, TickListPriority tickListPriority) {
+        this.schedule(blockPosition, t, i + this.currentTick, tickListPriority);
+    }
+
+    public void schedule(final NextTickListEntry<T> entry) {
+        this.schedule(entry.getPosition(), entry.getData(), entry.getTargetTick(), entry.getPriority());
+    }
+
+    public void schedule(final BlockPosition pos, final T data, final long targetTick, final TickListPriority priority) {
+        final NextTickListEntry<T> entry = new NextTickListEntry<>(pos, data, targetTick, priority);
+        if (this.excludeFromScheduling.test(entry.getData())) {
+            return;
+        }
+
+        if (WARN_ON_EXCESSIVE_DELAY) {
+            final long delay = entry.getTargetTick() - this.currentTick;
+            if (delay >= EXCESSIVE_DELAY_THRESHOLD) {
+                MinecraftServer.LOGGER.warn("Entry " + entry.toString() + " has been scheduled with an excessive delay of: " + delay, new Throwable());
+            }
+        }
+
+        final long blockKey = MCUtil.getBlockKey(pos);
+
+        final ArrayList<NextTickListEntry<T>> currentEntries = this.entriesByBlock.computeIfAbsent(blockKey, (long keyInMap) -> new ArrayList<>(3));
+
+        if (currentEntries.isEmpty()) {
+            currentEntries.add(entry);
+        } else {
+            for (int i = 0, size = currentEntries.size(); i < size; ++i) {
+                final NextTickListEntry<T> currentEntry = currentEntries.get(i);
+
+                // entries are only blocked from scheduling if currentEntry.equals(toSchedule) && currentEntry is scheduled to tick (NOT including pending)
+                if (currentEntry.getData() == entry.getData() && currentEntry.tickState == STATE_SCHEDULED) {
+                    // can't add
+                    return;
+                }
+            }
+            currentEntries.add(entry);
+        }
+
+        entry.tickState = STATE_SCHEDULED;
+
+        this.entriesByChunk.computeIfAbsent(MCUtil.getCoordinateKey(entry.getPosition()), (final long keyInMap) -> {
+            return new ObjectRBTreeSet<>(TickListServerInterval.ENTRY_COMPARATOR);
+        }).add(entry);
+
+        this.addToSchedule(entry);
+    }
+
+    public void scheduleAll(final Iterator<NextTickListEntry<T>> iterator) {
+        while (iterator.hasNext()) {
+            this.schedule(iterator.next());
+        }
+    }
+
+    // this is not the standard interception calculation, but it's the one vanilla uses
+    // i.e the y value is ignored? the x, z calc isn't correct?
+    // however for the copy op they use the correct intersection, after using this one of course...
+    private static boolean isBlockInSortof(final StructureBoundingBox boundingBox, final BlockPosition pos) {
+        return pos.getX() >= boundingBox.getMinX() && pos.getX() < boundingBox.getMaxX() && pos.getZ() >= boundingBox.getMinZ() && pos.getZ() < boundingBox.getMaxZ();
+    }
+
+    @Override
+    public List<NextTickListEntry<T>> getEntriesInBoundingBox(final StructureBoundingBox structureboundingbox, final boolean removeReturned, final boolean excludeTicked) {
+        if (structureboundingbox.getMinX() == structureboundingbox.getMaxX() || structureboundingbox.getMinZ() == structureboundingbox.getMaxZ()) {
+            return Collections.emptyList(); // vanilla behaviour, check isBlockInSortof above
+        }
+
+        final int lowerChunkX = structureboundingbox.getMinX() >> 4;
+        final int upperChunkX = (structureboundingbox.getMaxX() - 1) >> 4; // subtract 1 since maxX is exclusive
+        final int lowerChunkZ = structureboundingbox.getMinZ() >> 4;
+        final int upperChunkZ = (structureboundingbox.getMaxZ() - 1) >> 4; // subtract 1 since maxZ is exclusive
+
+        final int xChunksLength = (upperChunkX - lowerChunkX + 1);
+        final int zChunksLength = (upperChunkZ - lowerChunkZ + 1);
+
+        final ObjectRBTreeSet<NextTickListEntry<T>>[] containingChunks = new ObjectRBTreeSet[xChunksLength * zChunksLength];
+
+        final int offset = (xChunksLength * -lowerChunkZ - lowerChunkX);
+        int totalEntries = 0;
+        for (int currChunkX = lowerChunkX; currChunkX <= upperChunkX; ++currChunkX) {
+            for (int currChunkZ = lowerChunkZ; currChunkZ <= upperChunkZ; ++currChunkZ) {
+                // todo optimize
+                //final int index = (currChunkX - lowerChunkX) + xChunksLength * (currChunkZ - lowerChunkZ);
+                final int index = offset + currChunkX + xChunksLength * currChunkZ;
+                final ObjectRBTreeSet<NextTickListEntry<T>> set = containingChunks[index] = this.entriesByChunk.get(MCUtil.getCoordinateKey(currChunkX, currChunkZ));
+                if (set != null) {
+                    totalEntries += set.size();
+                }
+            }
+        }
+
+        final List<NextTickListEntry<T>> ret = new ArrayList<>(totalEntries);
+
+        final int matchOne = (STATE_SCHEDULED | STATE_PENDING_TICK) | (excludeTicked ? 0 : (STATE_TICKING | STATE_TICKED));
+
+        MCUtil.mergeSortedSets((NextTickListEntry<T> entry) -> {
+            if (!isBlockInSortof(structureboundingbox, entry.getPosition())) {
+                return;
+            }
+            final int tickState = entry.tickState;
+            if ((tickState & matchOne) == 0) {
+                return;
+            }
+
+            ret.add(entry);
+            return;
+        }, TickListServerInterval.ENTRY_COMPARATOR, containingChunks);
+
+        if (removeReturned) {
+            for (NextTickListEntry<T> entry : ret) {
+                this.removeEntry(entry);
+            }
+        }
+
+        return ret;
+    }
+
+    @Override
+    public void copy(StructureBoundingBox structureboundingbox, BlockPosition blockposition) {
+        // start copy from TickListServer // TODO check on update
+        List<NextTickListEntry<T>> list = this.getEntriesInBoundingBox(structureboundingbox, false, false);
+        Iterator<NextTickListEntry<T>> iterator = list.iterator();
+
+        while (iterator.hasNext()) {
+            NextTickListEntry<T> nextticklistentry = iterator.next();
+
+            if (structureboundingbox.hasPoint( nextticklistentry.getPosition())) {
+                BlockPosition blockposition1 = nextticklistentry.getPosition().add(blockposition);
+                T t0 = nextticklistentry.getData();
+
+                this.schedule(new NextTickListEntry<>(blockposition1, t0, nextticklistentry.getTargetTick(), nextticklistentry.getPriority()));
+            }
+        }
+        // end copy from TickListServer
+    }
+
+    @Override
+    public List<NextTickListEntry<T>> getEntriesInChunk(ChunkCoordIntPair chunkPos, boolean removeReturned, boolean excludeTicked) {
+        // Vanilla DOES get the entries 2 blocks out of the chunk too, but that doesn't matter since we ignore chunks
+        // not at ticking status, and ticking status requires neighbours loaded
+        // so with this method we will reduce scheduler churning
+        final int matchOne = (STATE_SCHEDULED | STATE_PENDING_TICK) | (excludeTicked ? 0 : (STATE_TICKING | STATE_TICKED));
+
+        final ObjectRBTreeSet<NextTickListEntry<T>> entries = this.entriesByChunk.get(MCUtil.getCoordinateKey(chunkPos));
+
+        if (entries == null) {
+            return Collections.emptyList();
+        }
+
+        final List<NextTickListEntry<T>> ret = new ArrayList<>(entries.size());
+
+        for (NextTickListEntry<T> entry : entries) {
+            if ((entry.tickState & matchOne) == 0) {
+                continue;
+            }
+            ret.add(entry);
+        }
+
+        if (removeReturned) {
+            for (NextTickListEntry<T> entry : ret) {
+                this.removeEntry(entry);
+            }
+        }
+
+        return ret;
+    }
+
+    @Override
+    public NBTTagList serialize(ChunkCoordIntPair chunkcoordintpair) {
+        // start copy from TickListServer  // TODO check on update
+        List<NextTickListEntry<T>> list = this.getEntriesInChunk(chunkcoordintpair, false, true);
+
+        return TickListServer.serialize(this.getMinecraftKeyFrom, list, this.currentTick);
+        // end copy from TickListServer
+    }
+
+    @Override
+    public int getTotalScheduledEntries() {
+        // good thing this is only used in debug reports // TODO check on update
+        int ret = 0;
+
+        for (NextTickListEntry<T> entry : this.longScheduled) {
+            if (entry.tickState == STATE_SCHEDULED) {
+                ++ret;
+            }
+        }
+
+        for (Iterator<Long2ObjectMap.Entry<ArrayList<NextTickListEntry<T>>>> iterator = this.pendingChunkTickLoad.long2ObjectEntrySet().iterator(); iterator.hasNext();) {
+            ArrayList<NextTickListEntry<T>> list = iterator.next().getValue();
+
+            for (NextTickListEntry<T> entry : list) {
+                if (entry.tickState == STATE_SCHEDULED) {
+                    ++ret;
+                }
+            }
+        }
+
+        for (TickListServerInterval<T> interval : this.shortScheduled) {
+            for (Iterable<NextTickListEntry<T>> set : interval.byPriority) {
+                for (NextTickListEntry<T> entry : set) {
+                    if (entry.tickState == STATE_SCHEDULED) {
+                        ++ret;
+                    }
+                }
+            }
+        }
+
+        return ret;
+    }
+}
diff --git a/src/main/java/com/destroystokyo/paper/server/ticklist/TickListServerInterval.java b/src/main/java/com/destroystokyo/paper/server/ticklist/TickListServerInterval.java
new file mode 100644
index 0000000000000000000000000000000000000000..13cf1a55a9babbffccbca1acfbe1c496e8925521
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/server/ticklist/TickListServerInterval.java
@@ -0,0 +1,41 @@
+package com.destroystokyo.paper.server.ticklist;
+
+import com.destroystokyo.paper.util.set.LinkedSortedSet;
+import net.minecraft.server.NextTickListEntry;
+import net.minecraft.server.TickListPriority;
+import java.util.Comparator;
+
+// represents a set of entries to tick at a specified time
+public final class TickListServerInterval<T> {
+
+    public static final int TOTAL_PRIORITIES = TickListPriority.values().length;
+    public static final Comparator<NextTickListEntry<?>> ENTRY_COMPARATOR_BY_ID = (entry1, entry2) -> {
+        return Long.compare(entry1.getId(), entry2.getId());
+    };
+    public static final Comparator<NextTickListEntry<?>> ENTRY_COMPARATOR = (Comparator)NextTickListEntry.comparator();
+
+    // we do not record the interval, this class is meant to be used on a ring buffer
+
+    // inlined enum map for TickListPriority
+    public final LinkedSortedSet<NextTickListEntry<T>>[] byPriority = new LinkedSortedSet[TOTAL_PRIORITIES];
+
+    {
+        for (int i = 0, len = this.byPriority.length; i < len; ++i) {
+            this.byPriority[i] = new LinkedSortedSet<>(ENTRY_COMPARATOR_BY_ID);
+        }
+    }
+
+    public void addEntryLast(final NextTickListEntry<T> entry) {
+        this.byPriority[entry.getPriority().ordinal()].addLast(entry);
+    }
+
+    public void addEntryFirst(final NextTickListEntry<T> entry) {
+        this.byPriority[entry.getPriority().ordinal()].addFirst(entry);
+    }
+
+    public void clear() {
+        for (int i = 0, len = this.byPriority.length; i < len; ++i) {
+            this.byPriority[i].clear(); // O(1) clear
+        }
+    }
+}
diff --git a/src/main/java/com/destroystokyo/paper/util/set/LinkedSortedSet.java b/src/main/java/com/destroystokyo/paper/util/set/LinkedSortedSet.java
new file mode 100644
index 0000000000000000000000000000000000000000..118988c39e58f28e8a2851792b9c014f341f06fc
--- /dev/null
+++ b/src/main/java/com/destroystokyo/paper/util/set/LinkedSortedSet.java
@@ -0,0 +1,142 @@
+package com.destroystokyo.paper.util.set;
+
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+public final class LinkedSortedSet<E> implements Iterable<E> {
+
+    public final Comparator<? super E> comparator;
+
+    protected Link<E> head;
+    protected Link<E> tail;
+
+    public LinkedSortedSet() {
+        this((Comparator)Comparator.naturalOrder());
+    }
+
+    public LinkedSortedSet(final Comparator<? super E> comparator) {
+        this.comparator = comparator;
+    }
+
+    public void clear() {
+        this.head = this.tail = null;
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
+
+            Link<E> next = LinkedSortedSet.this.head;
+
+            @Override
+            public boolean hasNext() {
+                return this.next != null;
+            }
+
+            @Override
+            public E next() {
+                final Link<E> next = this.next;
+                if (next == null) {
+                    throw new NoSuchElementException();
+                }
+                this.next = next.next;
+                return next.element;
+            }
+        };
+    }
+
+    public boolean addLast(final E element) {
+        final Comparator<? super E> comparator = this.comparator;
+
+        Link<E> curr = this.tail;
+        if (curr != null) {
+            int compare;
+
+            while ((compare = comparator.compare(element, curr.element)) < 0) {
+                Link<E> prev = curr;
+                curr = curr.prev;
+                if (curr != null) {
+                    continue;
+                }
+                this.head = prev.prev = new Link<>(element, null, prev);
+                return true;
+            }
+
+            if (compare != 0) {
+                // insert after curr
+                final Link<E> next = curr.next;
+                final Link<E> insert = new Link<>(element, curr, next);
+                curr.next = insert;
+
+                if (next == null) {
+                    this.tail = insert;
+                } else {
+                    next.prev = insert;
+                }
+                return true;
+            }
+
+            return false;
+        } else {
+            this.head = this.tail = new Link<>(element);
+            return true;
+        }
+    }
+
+    public boolean addFirst(final E element) {
+        final Comparator<? super E> comparator = this.comparator;
+
+        Link<E> curr = this.head;
+        if (curr != null) {
+            int compare;
+
+            while ((compare = comparator.compare(element, curr.element)) > 0) {
+                Link<E> prev = curr;
+                curr = curr.next;
+                if (curr != null) {
+                    continue;
+                }
+                this.tail = prev.next = new Link<>(element, prev, null);
+                return true;
+            }
+
+            if (compare != 0) {
+                // insert before curr
+                final Link<E> prev = curr.prev;
+                final Link<E> insert = new Link<>(element, prev, curr);
+                curr.prev = insert;
+
+                if (prev == null) {
+                    this.head = insert;
+                } else {
+                    prev.next = insert;
+                }
+                return true;
+            }
+
+            return false;
+        } else {
+            this.head = this.tail = new Link<>(element);
+            return true;
+        }
+    }
+
+    protected static final class Link<E> {
+        public E element;
+        public Link<E> prev;
+        public Link<E> next;
+
+        public Link() {}
+
+        public Link(final E element) {
+            this.element = element;
+        }
+
+        public Link(final E element, final Link<E> prev, final Link<E> next) {
+            this.element = element;
+            this.prev = prev;
+            this.next = next;
+        }
+    }
+}
diff --git a/src/main/java/net/minecraft/server/BlockPosition.java b/src/main/java/net/minecraft/server/BlockPosition.java
index 253423acc3c3697a5e47136f34da92617e719753..52ae74571b0d671a294900caedaa400b62d4ea34 100644
--- a/src/main/java/net/minecraft/server/BlockPosition.java
+++ b/src/main/java/net/minecraft/server/BlockPosition.java
@@ -105,6 +105,7 @@ public class BlockPosition extends BaseBlockPosition {
         return i == 0 && j == 0 && k == 0 ? this : new BlockPosition(this.getX() + i, this.getY() + j, this.getZ() + k);
     }
 
+    public final BlockPosition add(BaseBlockPosition baseblockposition) { return this.a(baseblockposition); } // Paper - OBFHELPER
     public BlockPosition a(BaseBlockPosition baseblockposition) {
         return this.b(baseblockposition.getX(), baseblockposition.getY(), baseblockposition.getZ());
     }
diff --git a/src/main/java/net/minecraft/server/ChunkProviderServer.java b/src/main/java/net/minecraft/server/ChunkProviderServer.java
index 45a91ab94f40ca9d8c469e468c6b66952babcf11..ce671ecabc402053b160df0f9d64d22b784d165c 100644
--- a/src/main/java/net/minecraft/server/ChunkProviderServer.java
+++ b/src/main/java/net/minecraft/server/ChunkProviderServer.java
@@ -203,6 +203,13 @@ public class ChunkProviderServer extends IChunkProvider {
     }
     // Paper end
 
+    // Paper start - rewrite ticklistserver
+    public final boolean isTickingReadyMainThread(BlockPosition pos) {
+        PlayerChunk chunk = this.playerChunkMap.getUpdatingChunk(MCUtil.getCoordinateKey(pos));
+        return chunk != null && chunk.isTickingReady();
+    }
+    // Paper end - rewrite ticklistserver
+
     public ChunkProviderServer(WorldServer worldserver, Convertable.ConversionSession convertable_conversionsession, DataFixer datafixer, DefinedStructureManager definedstructuremanager, Executor executor, ChunkGenerator chunkgenerator, int i, boolean flag, WorldLoadListener worldloadlistener, Supplier<WorldPersistentData> supplier) {
         this.world = worldserver;
         this.serverThreadQueue = new ChunkProviderServer.a(worldserver);
diff --git a/src/main/java/net/minecraft/server/NextTickListEntry.java b/src/main/java/net/minecraft/server/NextTickListEntry.java
index 33cfeabdee03195a294f303f28044a313cb1c4ed..2287e47d1b891135a5f2579ec324c70589141192 100644
--- a/src/main/java/net/minecraft/server/NextTickListEntry.java
+++ b/src/main/java/net/minecraft/server/NextTickListEntry.java
@@ -5,11 +5,13 @@ import java.util.Comparator;
 public class NextTickListEntry<T> {
 
     private static final java.util.concurrent.atomic.AtomicLong COUNTER = new java.util.concurrent.atomic.AtomicLong(); // Paper - async chunk loading
-    private final T e;
-    public final BlockPosition a;
-    public final long b;
-    public final TickListPriority c;
-    private final long f;
+    private final T e; public final T getData() { return this.e; } // Paper - OBFHELPER
+    public final BlockPosition a; public final BlockPosition getPosition() { return this.a; } // Paper - OBFHELPER
+    public final long b; public final long getTargetTick() { return this.b; } // Paper - OBFHELPER
+    public final TickListPriority c; public final TickListPriority getPriority() { return this.c; } // Paper - OBFHELPER
+    private final long f; public final long getId() { return this.f; } // Paper - OBFHELPER
+    private final int hash; // Paper
+    public int tickState; // Paper
 
     public NextTickListEntry(BlockPosition blockposition, T t0) {
         this(blockposition, t0, 0L, TickListPriority.NORMAL);
@@ -21,6 +23,7 @@ public class NextTickListEntry<T> {
         this.e = t0;
         this.b = i;
         this.c = ticklistpriority;
+        this.hash = this.computeHash(); // Paper
     }
 
     public boolean equals(Object object) {
@@ -33,19 +36,31 @@ public class NextTickListEntry<T> {
         }
     }
 
+    // Paper start - optimize hashcode
+    @Override
     public int hashCode() {
+        return this.hash;
+    }
+    public final int computeHash() {
+        // Paper end - optimize hashcode
         return this.a.hashCode();
     }
 
-    public static <T> Comparator<Object> a() { // Paper - decompile fix
-        return Comparator.comparingLong((nextticklistentry) -> {
-            return ((NextTickListEntry<T>) nextticklistentry).b; // Paper - decompile fix
-        }).thenComparing((nextticklistentry) -> {
-            return ((NextTickListEntry<T>) nextticklistentry).c; // Paper - decompile fix
-        }).thenComparingLong((nextticklistentry) -> {
-            return ((NextTickListEntry<T>) nextticklistentry).f; // Paper - decompile fix
-        });
+    // Paper start - let's not use more functional code for no reason.
+    public static <T> Comparator<Object> comparator() { return NextTickListEntry.a(); } // Paper - OBFHELPER
+    public static <T> Comparator<Object> a() {
+        return (Comparator)(Comparator<NextTickListEntry>)(NextTickListEntry nextticklistentry, NextTickListEntry nextticklistentry1) -> {
+            int i = Long.compare(nextticklistentry.getTargetTick(), nextticklistentry1.getTargetTick());
+
+            if (i != 0) {
+                return i;
+            } else {
+                i = nextticklistentry.getPriority().compareTo(nextticklistentry1.getPriority());
+                return i != 0 ? i : Long.compare(nextticklistentry.getId(), nextticklistentry1.getId());
+            }
+        };
     }
+    // Paper end - let's not use more functional code for no reason.
 
     public String toString() {
         return this.e + ": " + this.a + ", " + this.b + ", " + this.c + ", " + this.f;
diff --git a/src/main/java/net/minecraft/server/PlayerChunk.java b/src/main/java/net/minecraft/server/PlayerChunk.java
index 301836c7d465afe82737b0aa5ad68bf51122ff6b..054a3156f7b7b7077422b4951adf7bf45df42bfc 100644
--- a/src/main/java/net/minecraft/server/PlayerChunk.java
+++ b/src/main/java/net/minecraft/server/PlayerChunk.java
@@ -467,7 +467,9 @@ public class PlayerChunk {
                     PlayerChunk.this.isTickingReady = true;
 
 
-
+                    // Paper start - rewrite ticklistserver
+                    PlayerChunk.this.chunkMap.world.onChunkSetTicking(PlayerChunk.this.location.x, PlayerChunk.this.location.z);
+                    // Paper end - rewrite ticklistserver
 
                 }
             });
diff --git a/src/main/java/net/minecraft/server/StructureBoundingBox.java b/src/main/java/net/minecraft/server/StructureBoundingBox.java
index 7873db26b336c97f909e5391e58ee53feaf59b9a..447eb2ba84789edf9bac2e2ffb2dec7cb4596cbf 100644
--- a/src/main/java/net/minecraft/server/StructureBoundingBox.java
+++ b/src/main/java/net/minecraft/server/StructureBoundingBox.java
@@ -4,12 +4,12 @@ import com.google.common.base.MoreObjects;
 
 public class StructureBoundingBox {
 
-    public int a;
-    public int b;
-    public int c;
-    public int d;
-    public int e;
-    public int f;
+    public int a; public final int getMinX() { return this.a; } // Paper - OBFHELPER
+    public int b; public final int getMinY() { return this.b; } // Paper - OBFHELPER
+    public int c; public final int getMinZ() { return this.c; } // Paper - OBFHELPER
+    public int d; public final int getMaxX() { return this.d; } // Paper - OBFHELPER
+    public int e; public final int getMaxY() { return this.e; } // Paper - OBFHELPER
+    public int f; public final int getMaxZ() { return this.f; } // Paper - OBFHELPER
 
     public StructureBoundingBox() {}
 
@@ -88,6 +88,7 @@ public class StructureBoundingBox {
         this.e = 512;
     }
 
+    public final boolean intersects(StructureBoundingBox boundingBox) { return this.b(boundingBox); } // Paper - OBFHELPER
     public boolean b(StructureBoundingBox structureboundingbox) {
         return this.d >= structureboundingbox.a && this.a <= structureboundingbox.d && this.f >= structureboundingbox.c && this.c <= structureboundingbox.f && this.e >= structureboundingbox.b && this.b <= structureboundingbox.e;
     }
@@ -122,6 +123,7 @@ public class StructureBoundingBox {
         this.a(baseblockposition.getX(), baseblockposition.getY(), baseblockposition.getZ());
     }
 
+    public final boolean hasPoint(BaseBlockPosition baseblockposition) { return this.b(baseblockposition); } // Paper - OBFHELPER
     public boolean b(BaseBlockPosition baseblockposition) {
         return baseblockposition.getX() >= this.a && baseblockposition.getX() <= this.d && baseblockposition.getZ() >= this.c && baseblockposition.getZ() <= this.f && baseblockposition.getY() >= this.b && baseblockposition.getY() <= this.e;
     }
diff --git a/src/main/java/net/minecraft/server/TickListChunk.java b/src/main/java/net/minecraft/server/TickListChunk.java
index f94234b0a247e378ff9056d6c418464d619a356b..8af1229c3da63a838b0bec1cafde1e41cf5cf551 100644
--- a/src/main/java/net/minecraft/server/TickListChunk.java
+++ b/src/main/java/net/minecraft/server/TickListChunk.java
@@ -57,6 +57,8 @@ public class TickListChunk<T> implements TickList<T> {
         return nbttaglist;
     }
 
+    private static final int MAX_TICK_DELAY = Integer.getInteger("paper.ticklist-max-tick-delay", -1).intValue(); // Paper - clean up broken entries
+
     public static <T> TickListChunk<T> a(NBTTagList nbttaglist, Function<T, MinecraftKey> function, Function<MinecraftKey, T> function1) {
         List<TickListChunk.a<T>> list = Lists.newArrayList();
 
@@ -67,7 +69,14 @@ public class TickListChunk<T> implements TickList<T> {
             if (t0 != null) {
                 BlockPosition blockposition = new BlockPosition(nbttagcompound.getInt("x"), nbttagcompound.getInt("y"), nbttagcompound.getInt("z"));
 
-                list.add(new TickListChunk.a<>(t0, blockposition, nbttagcompound.getInt("t"), TickListPriority.a(nbttagcompound.getInt("p"))));
+                // Paper start - clean up broken entries
+                int delay = nbttagcompound.getInt("t");
+                if (MAX_TICK_DELAY > 0 && delay > MAX_TICK_DELAY) {
+                    MinecraftServer.LOGGER.warn("Dropping tick for pos " + blockposition + ", tick delay " + delay);
+                    continue;
+                }
+                list.add(new TickListChunk.a<>(t0, blockposition, delay, TickListPriority.a(nbttagcompound.getInt("p"))));
+                // Paper end - clean up broken entries
             }
         }
 
diff --git a/src/main/java/net/minecraft/server/TickListServer.java b/src/main/java/net/minecraft/server/TickListServer.java
index 3b8f56c0f0507ebdd9ac20be70688b4c0cfe4cf8..3e148b7e99554a1abe257dd3c9acafb914e1ebc8 100644
--- a/src/main/java/net/minecraft/server/TickListServer.java
+++ b/src/main/java/net/minecraft/server/TickListServer.java
@@ -38,7 +38,16 @@ public class TickListServer<T> implements TickList<T> {
     private final co.aikar.timings.Timing timingTicking; // Paper
     // Paper end
 
+    // Paper start
+    protected void nextTick() {}
+    // Paper end
+
     public void b() {
+        // Paper start - allow overriding
+        this.tick();
+    }
+    public void tick() {
+        // Paper end
         int i = this.nextTickList.size();
 
         if (false) { // CraftBukkit
@@ -106,10 +115,20 @@ public class TickListServer<T> implements TickList<T> {
 
     @Override
     public boolean b(BlockPosition blockposition, T t0) {
+        // Paper start - allow overriding
+        return this.isPendingTickThisTick(blockposition, t0);
+    }
+    public boolean isPendingTickThisTick(BlockPosition blockposition, T t0) {
+        // Paper end
         return this.f.contains(new NextTickListEntry<>(blockposition, t0));
     }
 
     public List<NextTickListEntry<T>> a(ChunkCoordIntPair chunkcoordintpair, boolean flag, boolean flag1) {
+        // Paper start - allow overriding
+        return this.getEntriesInChunk(chunkcoordintpair, flag, flag1);
+    }
+    public List<NextTickListEntry<T>> getEntriesInChunk(ChunkCoordIntPair chunkcoordintpair, boolean flag, boolean flag1) {
+        // Paper end
         int i = (chunkcoordintpair.x << 4) - 2;
         int j = i + 16 + 2;
         int k = (chunkcoordintpair.z << 4) - 2;
@@ -119,6 +138,11 @@ public class TickListServer<T> implements TickList<T> {
     }
 
     public List<NextTickListEntry<T>> a(StructureBoundingBox structureboundingbox, boolean flag, boolean flag1) {
+        // Paper start - allow overriding
+        return this.getEntriesInBoundingBox(structureboundingbox, flag, flag1);
+    }
+    public List<NextTickListEntry<T>> getEntriesInBoundingBox(StructureBoundingBox structureboundingbox, boolean flag, boolean flag1) {
+        // Paper end
         List<NextTickListEntry<T>> list = this.a((List) null, this.nextTickList, structureboundingbox, flag);
 
         if (flag && list != null) {
@@ -158,6 +182,11 @@ public class TickListServer<T> implements TickList<T> {
     }
 
     public void a(StructureBoundingBox structureboundingbox, BlockPosition blockposition) {
+        // Paper start - allow overriding
+        this.copy(structureboundingbox, blockposition);
+    }
+    public void copy(StructureBoundingBox structureboundingbox, BlockPosition blockposition) {
+        // Paper end
         List<NextTickListEntry<T>> list = this.a(structureboundingbox, false, false);
         Iterator iterator = list.iterator();
 
@@ -175,11 +204,17 @@ public class TickListServer<T> implements TickList<T> {
     }
 
     public NBTTagList a(ChunkCoordIntPair chunkcoordintpair) {
+        // Paper start - allow overriding
+        return this.serialize(chunkcoordintpair);
+    }
+    public NBTTagList serialize(ChunkCoordIntPair chunkcoordintpair) {
+        // Paper end
         List<NextTickListEntry<T>> list = this.a(chunkcoordintpair, false, true);
 
         return a(this.b, list, this.e.getTime());
     }
 
+    public static <T> NBTTagList serialize(Function<T, MinecraftKey> function, Iterable<NextTickListEntry<T>> iterable, long i) { return TickListServer.a(function, iterable, i); } // Paper - OBFHELPER
     private static <T> NBTTagList a(Function<T, MinecraftKey> function, Iterable<NextTickListEntry<T>> iterable, long i) {
         NBTTagList nbttaglist = new NBTTagList();
         Iterator iterator = iterable.iterator();
@@ -202,11 +237,21 @@ public class TickListServer<T> implements TickList<T> {
 
     @Override
     public boolean a(BlockPosition blockposition, T t0) {
+        // Paper start - allow overriding
+        return this.isScheduledForTick(blockposition, t0);
+    }
+    public boolean isScheduledForTick(BlockPosition blockposition, T t0) {
+        // Paper end
         return this.nextTickListHash.contains(new NextTickListEntry<>(blockposition, t0));
     }
 
     @Override
     public void a(BlockPosition blockposition, T t0, int i, TickListPriority ticklistpriority) {
+        // Paper start - allow overriding
+        this.schedule(blockposition, t0, i, ticklistpriority);
+    }
+    public void schedule(BlockPosition blockposition, T t0, int i, TickListPriority ticklistpriority) {
+        // Paper end
         if (!this.a.test(t0)) {
             this.a(new NextTickListEntry<>(blockposition, t0, (long) i + this.e.getTime(), ticklistpriority));
         }
@@ -222,6 +267,11 @@ public class TickListServer<T> implements TickList<T> {
     }
 
     public int a() {
+        // Paper start - allow overriding
+        return this.getTotalScheduledEntries();
+    }
+    public int getTotalScheduledEntries() {
+        // Paper end
         return this.nextTickListHash.size();
     }
 }
diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
index 52b1f4afc47d91603e1829275daecf8e9dd4cb1f..f816b3baf956729ffa8b404cc1baa5e64888e714 100644
--- a/src/main/java/net/minecraft/server/WorldServer.java
+++ b/src/main/java/net/minecraft/server/WorldServer.java
@@ -186,6 +186,15 @@ public class WorldServer extends World implements GeneratorAccessSeed {
     }
     // Paper end
 
+    // Paper start - rewrite ticklistserver
+    void onChunkSetTicking(int chunkX, int chunkZ) {
+        if (com.destroystokyo.paper.PaperConfig.useOptimizedTickList) {
+            ((com.destroystokyo.paper.server.ticklist.PaperTickList) this.nextTickListBlock).onChunkSetTicking(chunkX, chunkZ);
+            ((com.destroystokyo.paper.server.ticklist.PaperTickList) this.nextTickListFluid).onChunkSetTicking(chunkX, chunkZ);
+        }
+    }
+    // Paper end - rewrite ticklistserver
+
     // Add env and gen to constructor, WorldData -> WorldDataServer
     public WorldServer(MinecraftServer minecraftserver, Executor executor, Convertable.ConversionSession convertable_conversionsession, IWorldDataServer iworlddataserver, ResourceKey<World> resourcekey, DimensionManager dimensionmanager, WorldLoadListener worldloadlistener, ChunkGenerator chunkgenerator, boolean flag, long i, List<MobSpawner> list, boolean flag1, org.bukkit.World.Environment env, org.bukkit.generator.ChunkGenerator gen) {
         super(iworlddataserver, resourcekey, dimensionmanager, minecraftserver::getMethodProfiler, false, flag, i, gen, env, executor); // Paper pass executor
@@ -193,12 +202,21 @@ public class WorldServer extends World implements GeneratorAccessSeed {
         convertable = convertable_conversionsession;
         uuid = WorldUUID.getUUID(convertable_conversionsession.folder.toFile());
         // CraftBukkit end
-        this.nextTickListBlock = new TickListServer<>(this, (block) -> {
-            return block == null || block.getBlockData().isAir();
-        }, IRegistry.BLOCK::getKey, this::b, "Blocks"); // Paper - Timings
-        this.nextTickListFluid = new TickListServer<>(this, (fluidtype) -> {
-            return fluidtype == null || fluidtype == FluidTypes.EMPTY;
-        }, IRegistry.FLUID::getKey, this::a, "Fluids"); // Paper - Timings
+        if (com.destroystokyo.paper.PaperConfig.useOptimizedTickList) {
+            this.nextTickListBlock = new com.destroystokyo.paper.server.ticklist.PaperTickList<>(this, (block) -> {
+                return block == null || block.getBlockData().isAir();
+            }, IRegistry.BLOCK::getKey, this::b, "Blocks"); // Paper - Timings
+            this.nextTickListFluid = new com.destroystokyo.paper.server.ticklist.PaperTickList<>(this, (fluidtype) -> {
+                return fluidtype == null || fluidtype == FluidTypes.EMPTY;
+            }, IRegistry.FLUID::getKey, this::a, "Fluids"); // Paper - Timings
+        } else {
+            this.nextTickListBlock = new TickListServer<>(this, (block) -> {
+                return block == null || block.getBlockData().isAir();
+            }, IRegistry.BLOCK::getKey, this::b, "Blocks"); // Paper - Timings
+            this.nextTickListFluid = new TickListServer<>(this, (fluidtype) -> {
+                return fluidtype == null || fluidtype == FluidTypes.EMPTY;
+            }, IRegistry.FLUID::getKey, this::a, "Fluids"); // Paper - Timings
+        }
         this.navigators = Sets.newHashSet();
         this.L = new ObjectLinkedOpenHashSet();
         this.Q = flag1;
@@ -531,7 +549,9 @@ public class WorldServer extends World implements GeneratorAccessSeed {
         if (this.Q) {
             long i = this.worldData.getTime() + 1L;
 
-            this.worldDataServer.setTime(i);
+            this.worldDataServer.setTime(i); // Paper - diff on change, we want the below to be ran right after this
+            this.nextTickListBlock.nextTick(); // Paper
+            this.nextTickListFluid.nextTick(); // Paper
             this.worldDataServer.u().a(this.server, i);
             if (this.worldData.q().getBoolean(GameRules.DO_DAYLIGHT_CYCLE)) {
                 this.setDayTime(this.worldData.getDayTime() + 1L);
