Add debug for sync chunk loads

This patch adds a tool to find calls to getChunkAt which would load
chunks, however it must be enabled by setting the startup flag
-Dpaper.debug-sync-loads=true

- To get a debug log for sync loads, the command is
  /paper syncloadinfo
- To clear clear the currently stored sync load info, use
  /paper syncloadinfo clear

paper-server/patches/sources/net/minecraft/server/level/ServerChunkCache.java.patch

@@ -14,12 +14,10 @@
  
      public ServerChunkCache(ServerLevel world, LevelStorageSource.LevelStorageAccess session, DataFixer dataFixer, StructureTemplateManager structureTemplateManager, Executor workerExecutor, ChunkGenerator chunkGenerator, int viewDistance, int simulationDistance, boolean dsync, ChunkProgressListener worldGenerationProgressListener, ChunkStatusUpdateListener chunkStatusChangeListener, Supplier<DimensionDataStorage> persistentStateManagerFactory) {
          this.level = world;
-@@ -93,8 +100,66 @@
+@@ -95,6 +102,64 @@
-         this.distanceManager = this.chunkMap.getDistanceManager();
-         this.distanceManager.updateSimulationDistance(simulationDistance);
          this.clearCache();
-+    }
+     }
-+
+ 
 +    // CraftBukkit start - properly implement isChunkLoaded
 +    public boolean isChunkLoaded(int chunkX, int chunkZ) {
 +        ChunkHolder chunk = this.chunkMap.getUpdatingChunkIfPresent(ChunkPos.asLong(chunkX, chunkZ));
@@ -50,8 +48,8 @@
 +
 +    public <T> void addTicketAtLevel(TicketType<T> ticketType, ChunkPos chunkPos, int ticketLevel, T identifier) {
 +        this.distanceManager.addTicket(ticketType, chunkPos, ticketLevel, identifier);
-     }
++    }
- 
++
 +    public <T> void removeTicketAtLevel(TicketType<T> ticketType, ChunkPos chunkPos, int ticketLevel, T identifier) {
 +        this.distanceManager.removeTicket(ticketType, chunkPos, ticketLevel, identifier);
 +    }
@@ -90,16 +88,18 @@
                          return ichunkaccess;
                      }
                  }
-@@ -151,7 +216,7 @@
+@@ -150,8 +215,9 @@
+ 
              Objects.requireNonNull(completablefuture);
              chunkproviderserver_b.managedBlock(completablefuture::isDone);
++            // com.destroystokyo.paper.io.SyncLoadFinder.logSyncLoad(this.level, x, z); // Paper - Add debug for sync chunk loads
              ChunkResult<ChunkAccess> chunkresult = (ChunkResult) completablefuture.join();
 -            ChunkAccess ichunkaccess1 = (ChunkAccess) chunkresult.orElse((Object) null);
 +            ChunkAccess ichunkaccess1 = (ChunkAccess) chunkresult.orElse(null); // CraftBukkit - decompile error
  
              if (ichunkaccess1 == null && create) {
                  throw (IllegalStateException) Util.pauseInIde(new IllegalStateException("Chunk not there when requested: " + chunkresult.getError()));
-@@ -231,7 +296,15 @@
+@@ -231,7 +297,15 @@
          int l = ChunkLevel.byStatus(leastStatus);
          ChunkHolder playerchunk = this.getVisibleChunkIfPresent(k);
  
@@ -116,7 +116,7 @@
              this.distanceManager.addTicket(TicketType.UNKNOWN, chunkcoordintpair, l, chunkcoordintpair);
              if (this.chunkAbsent(playerchunk, l)) {
                  ProfilerFiller gameprofilerfiller = Profiler.get();
-@@ -250,7 +323,7 @@
+@@ -250,7 +324,7 @@
      }
  
      private boolean chunkAbsent(@Nullable ChunkHolder holder, int maxLevel) {
@@ -125,7 +125,7 @@
      }
  
      @Override
-@@ -279,7 +352,7 @@
+@@ -279,7 +353,7 @@
          return this.mainThreadProcessor.pollTask();
      }
  
@@ -134,7 +134,7 @@
          boolean flag = this.distanceManager.runAllUpdates(this.chunkMap);
          boolean flag1 = this.chunkMap.promoteChunkMap();
  
-@@ -309,18 +382,40 @@
+@@ -309,18 +383,40 @@
  
      @Override
      public void close() throws IOException {
@@ -177,7 +177,7 @@
              this.distanceManager.purgeStaleTickets();
          }
  
-@@ -401,14 +496,22 @@
+@@ -401,14 +497,22 @@
  
          this.lastSpawnState = spawnercreature_d;
          profiler.popPush("spawnAndTick");
@@ -203,7 +203,7 @@
          } else {
              list1 = List.of();
          }
-@@ -420,7 +523,7 @@
+@@ -420,7 +524,7 @@
              ChunkPos chunkcoordintpair = chunk.getPos();
  
              chunk.incrementInhabitedTime(timeDelta);
@@ -212,7 +212,7 @@
                  NaturalSpawner.spawnForChunk(this.level, chunk, spawnercreature_d, list1);
              }
  
-@@ -541,10 +644,16 @@
+@@ -541,10 +645,16 @@
  
      @Override
      public void setSpawnSettings(boolean spawnMonsters) {
@@ -231,7 +231,7 @@
      public String getChunkDebugData(ChunkPos pos) {
          return this.chunkMap.getChunkDebugData(pos);
      }
-@@ -618,14 +727,20 @@
+@@ -618,14 +728,20 @@
          }
  
          @Override

paper-server/patches/sources/net/minecraft/server/level/ServerLevel.java.patch

@@ -61,7 +61,7 @@
      private int lastSpawnChunkRadius;
      final EntityTickList entityTickList = new EntityTickList();
      public final PersistentEntitySectionManager<Entity> entityManager;
-@@ -214,52 +226,194 @@
+@@ -214,54 +226,203 @@
      private final boolean tickTime;
      private final RandomSequences randomSequences;
  
@@ -129,7 +129,7 @@
 +        }
 +        int minBlockX = Mth.floor(axisalignedbb.minX - 1.0E-7D) - 3;
 +        int minBlockZ = Mth.floor(axisalignedbb.minZ - 1.0E-7D) - 3;
-+
+ 
 +        int maxBlockX = Mth.floor(axisalignedbb.maxX + 1.0E-7D) + 3;
 +        int maxBlockZ = Mth.floor(axisalignedbb.maxZ + 1.0E-7D) + 3;
 +
@@ -209,7 +209,7 @@
 +        ChunkGenerator chunkgenerator = worlddimension.generator();
 +        // CraftBukkit start
 +        this.serverLevelData.setWorld(this);
- 
++
 +        if (biomeProvider != null) {
 +            BiomeSource worldChunkManager = new CustomWorldChunkManager(this.getWorld(), biomeProvider, this.server.registryAccess().lookupOrThrow(Registries.BIOME));
 +            if (chunkgenerator instanceof NoiseBasedChunkGenerator cga) {
@@ -279,8 +279,17 @@
 +        this.getCraftServer().addWorld(this.getWorld()); // CraftBukkit
      }
  
++    // Paper start
++    @Override
++    public boolean hasChunk(int chunkX, int chunkZ) {
++        return this.getChunkSource().getChunkAtIfLoadedImmediately(chunkX, chunkZ) != null;
++    }
++    // Paper end
++
      /** @deprecated */
-@@ -305,12 +459,20 @@
+     @Deprecated
+     @VisibleForTesting
+@@ -305,12 +466,20 @@
          long j;
  
          if (this.sleepStatus.areEnoughSleeping(i) && this.sleepStatus.areEnoughDeepSleeping(i, this.players)) {
@@ -304,7 +313,7 @@
              if (this.getGameRules().getBoolean(GameRules.RULE_WEATHER_CYCLE) && this.isRaining()) {
                  this.resetWeatherCycle();
              }
-@@ -345,7 +507,7 @@
+@@ -345,7 +514,7 @@
  
          this.handlingTick = false;
          gameprofilerfiller.pop();
@@ -313,7 +322,7 @@
  
          if (flag1) {
              this.resetEmptyTime();
-@@ -359,6 +521,7 @@
+@@ -359,6 +528,7 @@
                  gameprofilerfiller.pop();
              }
  
@@ -321,7 +330,7 @@
              this.entityTickList.forEach((entity) -> {
                  if (!entity.isRemoved()) {
                      if (!tickratemanager.isEntityFrozen(entity)) {
-@@ -429,7 +592,7 @@
+@@ -429,7 +599,7 @@
  
      private void wakeUpAllPlayers() {
          this.sleepStatus.removeAllSleepers();
@@ -330,7 +339,7 @@
              entityplayer.stopSleepInBed(false, false);
          });
      }
-@@ -442,12 +605,12 @@
+@@ -442,12 +612,12 @@
          ProfilerFiller gameprofilerfiller = Profiler.get();
  
          gameprofilerfiller.push("thunder");
@@ -345,7 +354,7 @@
  
                  if (flag1) {
                      SkeletonHorse entityhorseskeleton = (SkeletonHorse) EntityType.SKELETON_HORSE.create(this, EntitySpawnReason.EVENT);
-@@ -456,7 +619,7 @@
+@@ -456,7 +626,7 @@
                          entityhorseskeleton.setTrap(true);
                          entityhorseskeleton.setAge(0);
                          entityhorseskeleton.setPos((double) blockposition.getX(), (double) blockposition.getY(), (double) blockposition.getZ());
@@ -354,7 +363,7 @@
                      }
                  }
  
-@@ -465,18 +628,20 @@
+@@ -465,18 +635,20 @@
                  if (entitylightning != null) {
                      entitylightning.moveTo(Vec3.atBottomCenterOf(blockposition));
                      entitylightning.setVisualOnly(flag1);
@@ -376,7 +385,7 @@
  
          gameprofilerfiller.popPush("tickBlocks");
          if (randomTickSpeed > 0) {
-@@ -521,7 +686,7 @@
+@@ -521,7 +693,7 @@
          Biome biomebase = (Biome) this.getBiome(blockposition1).value();
  
          if (biomebase.shouldFreeze(this, blockposition2)) {
@@ -385,7 +394,7 @@
          }
  
          if (this.isRaining()) {
-@@ -537,10 +702,10 @@
+@@ -537,10 +709,10 @@
                          BlockState iblockdata1 = (BlockState) iblockdata.setValue(SnowLayerBlock.LAYERS, j + 1);
  
                          Block.pushEntitiesUp(iblockdata, iblockdata1, this, blockposition1);
@@ -398,7 +407,7 @@
                  }
              }
  
-@@ -701,33 +866,67 @@
+@@ -701,33 +873,67 @@
              this.rainLevel = Mth.clamp(this.rainLevel, 0.0F, 1.0F);
          }
  
@@ -474,7 +483,7 @@
      }
  
      public void resetEmptyTime() {
-@@ -754,6 +953,13 @@
+@@ -754,6 +960,13 @@
      }
  
      public void tickNonPassenger(Entity entity) {
@@ -488,7 +497,7 @@
          entity.setOldPosAndRot();
          ProfilerFiller gameprofilerfiller = Profiler.get();
  
-@@ -763,6 +969,7 @@
+@@ -763,6 +976,7 @@
          });
          gameprofilerfiller.incrementCounter("tickNonPassenger");
          entity.tick();
@@ -496,7 +505,7 @@
          gameprofilerfiller.pop();
          Iterator iterator = entity.getPassengers().iterator();
  
-@@ -786,6 +993,7 @@
+@@ -786,6 +1000,7 @@
                  });
                  gameprofilerfiller.incrementCounter("tickPassenger");
                  passenger.rideTick();
@@ -504,7 +513,7 @@
                  gameprofilerfiller.pop();
                  Iterator iterator = passenger.getPassengers().iterator();
  
-@@ -810,6 +1018,7 @@
+@@ -810,6 +1025,7 @@
          ServerChunkCache chunkproviderserver = this.getChunkSource();
  
          if (!savingDisabled) {
@@ -512,7 +521,7 @@
              if (progressListener != null) {
                  progressListener.progressStartNoAbort(Component.translatable("menu.savingLevel"));
              }
-@@ -827,11 +1036,19 @@
+@@ -827,11 +1043,19 @@
              }
  
          }
@@ -533,7 +542,7 @@
          }
  
          DimensionDataStorage worldpersistentdata = this.getChunkSource().getDataStorage();
-@@ -903,18 +1120,40 @@
+@@ -903,18 +1127,40 @@
  
      @Override
      public boolean addFreshEntity(Entity entity) {
@@ -577,7 +586,7 @@
          }
  
      }
-@@ -939,41 +1178,93 @@
+@@ -939,41 +1185,93 @@
          this.entityManager.addNewEntity(player);
      }
  
@@ -676,7 +685,7 @@
          while (iterator.hasNext()) {
              ServerPlayer entityplayer = (ServerPlayer) iterator.next();
  
-@@ -982,6 +1273,12 @@
+@@ -982,6 +1280,12 @@
                  double d1 = (double) pos.getY() - entityplayer.getY();
                  double d2 = (double) pos.getZ() - entityplayer.getZ();
  
@@ -689,7 +698,7 @@
                  if (d0 * d0 + d1 * d1 + d2 * d2 < 1024.0D) {
                      entityplayer.connection.send(new ClientboundBlockDestructionPacket(entityId, pos, progress));
                  }
-@@ -1030,7 +1327,7 @@
+@@ -1030,7 +1334,7 @@
  
      @Override
      public void levelEvent(@Nullable Player player, int eventId, BlockPos pos, int data) {
@@ -698,7 +707,7 @@
      }
  
      public int getLogicalHeight() {
-@@ -1060,7 +1357,18 @@
+@@ -1060,7 +1364,18 @@
              Iterator iterator = this.navigatingMobs.iterator();
  
              while (iterator.hasNext()) {
@@ -718,7 +727,7 @@
                  PathNavigation navigationabstract = entityinsentient.getNavigation();
  
                  if (navigationabstract.shouldRecomputePath(pos)) {
-@@ -1086,11 +1394,13 @@
+@@ -1086,11 +1401,13 @@
  
      @Override
      public void updateNeighborsAt(BlockPos pos, Block block) {
@@ -732,7 +741,7 @@
          this.neighborUpdater.updateNeighborsAtExceptFromFacing(pos, sourceBlock, (Direction) null, orientation);
      }
  
-@@ -1126,9 +1436,20 @@
+@@ -1126,9 +1443,20 @@
  
      @Override
      public void explode(@Nullable Entity entity, @Nullable DamageSource damageSource, @Nullable ExplosionDamageCalculator behavior, double x, double y, double z, float power, boolean createFire, Level.ExplosionInteraction explosionSourceType, ParticleOptions smallParticle, ParticleOptions largeParticle, Holder<SoundEvent> soundEvent) {
@@ -754,7 +763,7 @@
              case NONE:
                  explosion_effect = Explosion.BlockInteraction.KEEP;
                  break;
-@@ -1144,16 +1465,27 @@
+@@ -1144,16 +1472,27 @@
              case TRIGGER:
                  explosion_effect = Explosion.BlockInteraction.TRIGGER_BLOCK;
                  break;
@@ -785,7 +794,7 @@
          Iterator iterator = this.players.iterator();
  
          while (iterator.hasNext()) {
-@@ -1162,10 +1494,11 @@
+@@ -1162,10 +1501,11 @@
              if (entityplayer.distanceToSqr(vec3d) < 4096.0D) {
                  Optional<Vec3> optional = Optional.ofNullable((Vec3) serverexplosion.getHitPlayers().get(entityplayer));
  
@@ -798,7 +807,7 @@
      }
  
      private Explosion.BlockInteraction getDestroyType(GameRules.Key<GameRules.BooleanValue> decayRule) {
-@@ -1226,17 +1559,29 @@
+@@ -1226,17 +1566,29 @@
      }
  
      public <T extends ParticleOptions> int sendParticles(T parameters, double x, double y, double z, int count, double offsetX, double offsetY, double offsetZ, double speed) {
@@ -834,7 +843,7 @@
                  ++j;
              }
          }
-@@ -1292,7 +1637,7 @@
+@@ -1292,7 +1644,7 @@
  
      @Nullable
      public BlockPos findNearestMapStructure(TagKey<Structure> structureTag, BlockPos pos, int radius, boolean skipReferencedStructures) {
@@ -843,7 +852,7 @@
              return null;
          } else {
              Optional<HolderSet.Named<Structure>> optional = this.registryAccess().lookupOrThrow(Registries.STRUCTURE).get(structureTag);
-@@ -1334,11 +1679,22 @@
+@@ -1334,11 +1686,22 @@
      @Nullable
      @Override
      public MapItemSavedData getMapData(MapId id) {
@@ -867,7 +876,7 @@
          this.getServer().overworld().getDataStorage().set(id.key(), state);
      }
  
-@@ -1649,6 +2005,11 @@
+@@ -1649,6 +2012,11 @@
      @Override
      public void blockUpdated(BlockPos pos, Block block) {
          if (!this.isDebug()) {
@@ -879,7 +888,7 @@
              this.updateNeighborsAt(pos, block);
          }
  
-@@ -1668,12 +2029,12 @@
+@@ -1668,12 +2036,12 @@
      }
  
      public boolean isFlat() {
@@ -894,7 +903,7 @@
      }
  
      @Nullable
-@@ -1696,7 +2057,7 @@
+@@ -1696,7 +2064,7 @@
      private static <T> String getTypeCount(Iterable<T> items, Function<T, String> classifier) {
          try {
              Object2IntOpenHashMap<String> object2intopenhashmap = new Object2IntOpenHashMap();
@@ -903,7 +912,7 @@
  
              while (iterator.hasNext()) {
                  T t0 = iterator.next();
-@@ -1705,7 +2066,7 @@
+@@ -1705,7 +2073,7 @@
                  object2intopenhashmap.addTo(s, 1);
              }
  
@@ -912,7 +921,7 @@
                  String s1 = (String) entry.getKey();
  
                  return s1 + ":" + entry.getIntValue();
-@@ -1717,6 +2078,7 @@
+@@ -1717,6 +2085,7 @@
  
      @Override
      public LevelEntityGetter<Entity> getEntities() {
@@ -920,7 +929,7 @@
          return this.entityManager.getEntityGetter();
      }
  
-@@ -1802,6 +2164,17 @@
+@@ -1802,6 +2171,17 @@
          return this.serverLevelData.getGameRules();
      }
  
@@ -938,7 +947,7 @@
      @Override
      public CrashReportCategory fillReportDetails(CrashReport report) {
          CrashReportCategory crashreportsystemdetails = super.fillReportDetails(report);
-@@ -1836,6 +2209,7 @@
+@@ -1836,6 +2216,7 @@
          }
  
          public void onTrackingStart(Entity entity) {
@@ -946,7 +955,7 @@
              ServerLevel.this.getChunkSource().addEntity(entity);
              if (entity instanceof ServerPlayer entityplayer) {
                  ServerLevel.this.players.add(entityplayer);
-@@ -1864,9 +2238,52 @@
+@@ -1864,9 +2245,52 @@
              }
  
              entity.updateDynamicGameEventListener(DynamicGameEventListener::add);
@@ -999,7 +1008,7 @@
              ServerLevel.this.getChunkSource().removeEntity(entity);
              if (entity instanceof ServerPlayer entityplayer) {
                  ServerLevel.this.players.remove(entityplayer);
-@@ -1895,6 +2312,15 @@
+@@ -1895,6 +2319,15 @@
              }
  
              entity.updateDynamicGameEventListener(DynamicGameEventListener::remove);

paper-server/src/main/java/com/destroystokyo/paper/io/SyncLoadFinder.java

@@ -0,0 +1,177 @@
+package com.destroystokyo.paper.io;
+
+import com.google.gson.JsonArray;
+import com.google.gson.JsonObject;
+import com.mojang.datafixers.util.Pair;
+import it.unimi.dsi.fastutil.longs.Long2IntMap;
+import it.unimi.dsi.fastutil.longs.Long2IntOpenHashMap;
+import it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.WeakHashMap;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.Level;
+
+public class SyncLoadFinder {
+
+    public static final boolean ENABLED = Boolean.getBoolean("paper.debug-sync-loads");
+
+    private static final WeakHashMap<Level, Object2ObjectOpenHashMap<ThrowableWithEquals, SyncLoadInformation>> SYNC_LOADS = new WeakHashMap<>();
+
+    private static final class SyncLoadInformation {
+
+        public int times;
+
+        public final Long2IntOpenHashMap coordinateTimes = new Long2IntOpenHashMap();
+    }
+
+    public static void clear() {
+        SYNC_LOADS.clear();
+    }
+
+    public static void logSyncLoad(final Level world, final int chunkX, final int chunkZ) {
+        if (!ENABLED) {
+            return;
+        }
+
+        final ThrowableWithEquals stacktrace = new ThrowableWithEquals(Thread.currentThread().getStackTrace());
+
+        SYNC_LOADS.compute(world, (final Level keyInMap, Object2ObjectOpenHashMap<ThrowableWithEquals, SyncLoadInformation> map) -> {
+            if (map == null) {
+                map = new Object2ObjectOpenHashMap<>();
+            }
+
+            map.compute(stacktrace, (ThrowableWithEquals keyInMap0, SyncLoadInformation valueInMap) -> {
+                if (valueInMap == null) {
+                    valueInMap = new SyncLoadInformation();
+                }
+
+                ++valueInMap.times;
+
+                valueInMap.coordinateTimes.compute(ChunkPos.asLong(chunkX, chunkZ), (Long keyInMap1, Integer valueInMap1) -> {
+                    return valueInMap1 == null ? Integer.valueOf(1) : Integer.valueOf(valueInMap1.intValue() + 1);
+                });
+
+                return valueInMap;
+            });
+
+            return map;
+        });
+    }
+
+    public static JsonObject serialize() {
+        final JsonObject ret = new JsonObject();
+
+        final JsonArray worldsData = new JsonArray();
+
+        for (final Map.Entry<Level, Object2ObjectOpenHashMap<ThrowableWithEquals, SyncLoadInformation>> entry : SYNC_LOADS.entrySet()) {
+            final Level world = entry.getKey();
+
+            final JsonObject worldData = new JsonObject();
+
+            worldData.addProperty("name", world.getWorld().getName());
+
+            final List<Pair<ThrowableWithEquals, SyncLoadInformation>> data = new ArrayList<>();
+
+            entry.getValue().forEach((ThrowableWithEquals stacktrace, SyncLoadInformation times) -> {
+                data.add(new Pair<>(stacktrace, times));
+            });
+
+            data.sort((Pair<ThrowableWithEquals, SyncLoadInformation> pair1, Pair<ThrowableWithEquals, SyncLoadInformation> pair2) -> {
+                return Integer.compare(pair2.getSecond().times, pair1.getSecond().times); // reverse order
+            });
+
+            final JsonArray stacktraces = new JsonArray();
+
+            for (Pair<ThrowableWithEquals, SyncLoadInformation> pair : data) {
+                final JsonObject stacktrace = new JsonObject();
+
+                stacktrace.addProperty("times", pair.getSecond().times);
+
+                final JsonArray traces = new JsonArray();
+
+                for (StackTraceElement element : pair.getFirst().stacktrace) {
+                    traces.add(String.valueOf(element));
+                }
+
+                stacktrace.add("stacktrace", traces);
+
+                final JsonArray coordinates = new JsonArray();
+
+                for (Long2IntMap.Entry coordinate : pair.getSecond().coordinateTimes.long2IntEntrySet()) {
+                    final long key = coordinate.getLongKey();
+                    final int times = coordinate.getIntValue();
+                    final ChunkPos chunkPos = new ChunkPos(key);
+                    coordinates.add("(" + chunkPos.x + "," + chunkPos.z + "): " + times);
+                }
+
+                stacktrace.add("coordinates", coordinates);
+
+                stacktraces.add(stacktrace);
+            }
+
+
+            worldData.add("stacktraces", stacktraces);
+            worldsData.add(worldData);
+        }
+
+        ret.add("worlds", worldsData);
+
+        return ret;
+    }
+
+    static final class ThrowableWithEquals {
+
+        private final StackTraceElement[] stacktrace;
+        private final int hash;
+
+        public ThrowableWithEquals(final StackTraceElement[] stacktrace) {
+            this.stacktrace = stacktrace;
+            this.hash = ThrowableWithEquals.hash(stacktrace);
+        }
+
+        public static int hash(final StackTraceElement[] stacktrace) {
+            int hash = 0;
+
+            for (int i = 0; i < stacktrace.length; ++i) {
+                hash *= 31;
+                hash += stacktrace[i].hashCode();
+            }
+
+            return hash;
+        }
+
+        @Override
+        public int hashCode() {
+            return this.hash;
+        }
+
+        @Override
+        public boolean equals(final Object obj) {
+            if (obj == null || obj.getClass() != this.getClass()) {
+                return false;
+            }
+
+            final ThrowableWithEquals other = (ThrowableWithEquals)obj;
+            final StackTraceElement[] otherStackTrace = other.stacktrace;
+
+            if (this.stacktrace.length != otherStackTrace.length || this.hash != other.hash) {
+                return false;
+            }
+
+            if (this == obj) {
+                return true;
+            }
+
+            for (int i = 0; i < this.stacktrace.length; ++i) {
+                if (!this.stacktrace[i].equals(otherStackTrace[i])) {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+    }
+}

paper-server/src/main/java/io/papermc/paper/command/PaperCommand.java

@@ -38,6 +38,7 @@ public final class PaperCommand extends Command {
         commands.put(Set.of("reload"), new ReloadCommand());
         commands.put(Set.of("version"), new VersionCommand());
         commands.put(Set.of("dumpplugins"), new DumpPluginsCommand());
+        commands.put(Set.of("syncloadinfo"), new SyncLoadInfoCommand());
 
         return commands.entrySet().stream()
             .flatMap(entry -> entry.getKey().stream().map(s -> Map.entry(s, entry.getValue())))

paper-server/src/main/java/io/papermc/paper/command/subcommands/SyncLoadInfoCommand.java

@@ -0,0 +1,88 @@
+package io.papermc.paper.command.subcommands;
+
+import com.destroystokyo.paper.io.SyncLoadFinder;
+import com.google.gson.JsonObject;
+import com.google.gson.internal.Streams;
+import com.google.gson.stream.JsonWriter;
+import io.papermc.paper.command.CommandUtil;
+import io.papermc.paper.command.PaperSubcommand;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.PrintStream;
+import java.io.StringWriter;
+import java.nio.charset.StandardCharsets;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+import java.util.List;
+
+import net.kyori.adventure.text.event.ClickEvent;
+import net.kyori.adventure.text.event.HoverEvent;
+import net.minecraft.server.MinecraftServer;
+import org.bukkit.command.CommandSender;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+import static net.kyori.adventure.text.Component.text;
+import static net.kyori.adventure.text.format.NamedTextColor.GRAY;
+import static net.kyori.adventure.text.format.NamedTextColor.GREEN;
+import static net.kyori.adventure.text.format.NamedTextColor.RED;
+import static net.kyori.adventure.text.format.NamedTextColor.WHITE;
+
+@DefaultQualifier(NonNull.class)
+public final class SyncLoadInfoCommand implements PaperSubcommand {
+    @Override
+    public boolean execute(final CommandSender sender, final String subCommand, final String[] args) {
+        this.doSyncLoadInfo(sender, args);
+        return true;
+    }
+
+    @Override
+    public List<String> tabComplete(final CommandSender sender, final String subCommand, final String[] args) {
+        return CommandUtil.getListMatchingLast(sender, args, "clear");
+    }
+
+    private static final DateTimeFormatter FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd_HH.mm.ss");
+
+    private void doSyncLoadInfo(final CommandSender sender, final String[] args) {
+        if (!SyncLoadFinder.ENABLED) {
+            String systemFlag = "-Dpaper.debug-sync-loads=true";
+            sender.sendMessage(text().color(RED).append(text("This command requires the server startup flag '")).append(
+                text(systemFlag, WHITE).clickEvent(ClickEvent.copyToClipboard(systemFlag))
+                                       .hoverEvent(HoverEvent.showText(text("Click to copy the system flag")))).append(
+                text("' to be set.")));
+            return;
+        }
+
+        if (args.length > 0 && args[0].equals("clear")) {
+            SyncLoadFinder.clear();
+            sender.sendMessage(text("Sync load data cleared.", GRAY));
+            return;
+        }
+
+        File file = new File(new File(new File("."), "debug"),
+            "sync-load-info-" + FORMATTER.format(LocalDateTime.now()) + ".txt");
+        file.getParentFile().mkdirs();
+        sender.sendMessage(text("Writing sync load info to " + file, GREEN));
+
+
+        try {
+            final JsonObject data = SyncLoadFinder.serialize();
+
+            StringWriter stringWriter = new StringWriter();
+            JsonWriter jsonWriter = new JsonWriter(stringWriter);
+            jsonWriter.setIndent(" ");
+            jsonWriter.setLenient(false);
+            Streams.write(data, jsonWriter);
+
+            try (
+                PrintStream out = new PrintStream(new FileOutputStream(file), false, StandardCharsets.UTF_8)
+            ) {
+                out.print(stringWriter);
+            }
+            sender.sendMessage(text("Successfully written sync load information!", GREEN));
+        } catch (Throwable thr) {
+            sender.sendMessage(text("Failed to write sync load information! See the console for more info.", RED));
+            MinecraftServer.LOGGER.warn("Error occurred while dumping sync chunk load info", thr);
+        }
+    }
+}