From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 16 Oct 2021 01:36:00 -0700
Subject: [PATCH] Do not overload I/O threads with chunk data while flush
 saving

If the chunk count is high, then the memory used by the
chunks adds up and could cause problems. By flushing
every so many chunks, the server will not become
stressed for memory. It will also not increase the total
time to save, as flush saving performs a full flush at
the end anyways.

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 236ba4c1950a3cced590f520b5349eede75fd59b..adce96d372e0f9b6c3813b2153a5dcbb32a4e75c 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -946,6 +946,16 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     // Paper end
 
     protected void saveAllChunks(boolean flush) {
+        // Paper start - do not overload I/O threads with too much work when saving
+        int[] saved = new int[1];
+        int maxAsyncSaves = 50;
+        Runnable onChunkSave = () -> {
+            if (++saved[0] >= maxAsyncSaves) {
+                saved[0] = 0;
+                com.destroystokyo.paper.io.PaperFileIOThread.Holder.INSTANCE.flush();
+            }
+        };
+        // Paper end - do not overload I/O threads with too much work when saving
         if (flush) {
             List<ChunkHolder> list = (List) this.updatingChunks.getVisibleValuesCopy().stream().filter(ChunkHolder::wasAccessibleSinceLastSave).peek(ChunkHolder::refreshAccessibility).collect(Collectors.toList()); // Paper
             MutableBoolean mutableboolean = new MutableBoolean();
@@ -968,6 +978,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                 }).filter((ichunkaccess) -> {
                     return ichunkaccess instanceof ImposterProtoChunk || ichunkaccess instanceof LevelChunk;
                 }).filter(this::save).forEach((ichunkaccess) -> {
+                    onChunkSave.run(); // Paper - do not overload I/O threads with too much work when saving
                     mutableboolean.setTrue();
                 });
             } while (mutableboolean.isTrue());
