From ffad9695545a4de346adc4b9185538ece42df143 Mon Sep 17 00:00:00 2001
From: carlosdelest <carlos.delgado@elastic.co>
Date: Tue, 23 Jan 2024 17:32:07 +0100
Subject: [PATCH] Allow choosing Direct IO using index setting

---
 .../common/settings/IndexScopedSettings.java  |  1 +
 .../org/elasticsearch/index/IndexModule.java  |  6 +++++
 .../index/store/FsDirectoryFactory.java       | 24 +++++++++++++------
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java b/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
index c1b8d51c255db..58f4343a45a85 100644
--- a/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
+++ b/server/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
@@ -157,6 +157,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
         MapperService.INDEX_MAPPING_FIELD_NAME_LENGTH_LIMIT_SETTING,
         BitsetFilterCache.INDEX_LOAD_RANDOM_ACCESS_FILTERS_EAGERLY_SETTING,
         IndexModule.INDEX_STORE_TYPE_SETTING,
+        IndexModule.INDEX_STORE_DIRECT_IO_SETTING,
         IndexModule.INDEX_STORE_PRE_LOAD_SETTING,
         IndexModule.INDEX_RECOVERY_TYPE_SETTING,
         IndexModule.INDEX_QUERY_CACHE_ENABLED_SETTING,
diff --git a/server/src/main/java/org/elasticsearch/index/IndexModule.java b/server/src/main/java/org/elasticsearch/index/IndexModule.java
index e380a3859deea..c840a1f5220a6 100644
--- a/server/src/main/java/org/elasticsearch/index/IndexModule.java
+++ b/server/src/main/java/org/elasticsearch/index/IndexModule.java
@@ -112,6 +112,12 @@ public final class IndexModule {
         Property.NodeScope
     );
 
+    public static final Setting<Boolean> INDEX_STORE_DIRECT_IO_SETTING = Setting.boolSetting(
+        "index.store.direct_io",
+        false,
+        Property.IndexScope
+    );
+
     public static final Setting<String> INDEX_RECOVERY_TYPE_SETTING = new Setting<>(
         "index.recovery.type",
         "",
diff --git a/server/src/main/java/org/elasticsearch/index/store/FsDirectoryFactory.java b/server/src/main/java/org/elasticsearch/index/store/FsDirectoryFactory.java
index 05c3554b47602..14c5fbf2ee980 100644
--- a/server/src/main/java/org/elasticsearch/index/store/FsDirectoryFactory.java
+++ b/server/src/main/java/org/elasticsearch/index/store/FsDirectoryFactory.java
@@ -8,6 +8,7 @@
 
 package org.elasticsearch.index.store;
 
+import org.apache.lucene.misc.store.DirectIODirectory;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.FSDirectory;
 import org.apache.lucene.store.FileSwitchDirectory;
@@ -61,23 +62,32 @@ protected Directory newFSDirectory(Path location, LockFactory lockFactory, Index
             type = IndexModule.Type.fromSettingsKey(storeType);
         }
         Set<String> preLoadExtensions = new HashSet<>(indexSettings.getValue(IndexModule.INDEX_STORE_PRE_LOAD_SETTING));
+        FSDirectory directory = null;
         switch (type) {
             case HYBRIDFS:
                 // Use Lucene defaults
-                final FSDirectory primaryDirectory = FSDirectory.open(location, lockFactory);
-                if (primaryDirectory instanceof MMapDirectory mMapDirectory) {
-                    return new HybridDirectory(lockFactory, setPreload(mMapDirectory, lockFactory, preLoadExtensions));
-                } else {
-                    return primaryDirectory;
+                directory = FSDirectory.open(location, lockFactory);
+                if (directory instanceof MMapDirectory mMapDirectory) {
+                    directory = new HybridDirectory(lockFactory, setPreload(mMapDirectory, lockFactory, preLoadExtensions));
                 }
+                break;
             case MMAPFS:
-                return setPreload(new MMapDirectory(location, lockFactory), lockFactory, preLoadExtensions);
+                directory = setPreload(new MMapDirectory(location, lockFactory), lockFactory, preLoadExtensions);
+                break;
             case SIMPLEFS:
             case NIOFS:
-                return new NIOFSDirectory(location, lockFactory);
+                directory = new NIOFSDirectory(location, lockFactory);
+                break;
             default:
                 throw new AssertionError("unexpected built-in store type [" + type + "]");
         }
+
+        final boolean useDirectIO = indexSettings.getValue(IndexModule.INDEX_STORE_DIRECT_IO_SETTING);
+        if (useDirectIO) {
+            return new DirectIODirectory(directory);
+        }
+
+        return directory;
     }
 
     public static MMapDirectory setPreload(MMapDirectory mMapDirectory, LockFactory lockFactory, Set<String> preLoadExtensions)