Make HybridDirectory MMAP Extensions Configurable

server/src/main/java/org/opensearch/common/settings/IndexScopedSettings.java

@@ -179,6 +179,7 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
                 BitsetFilterCache.INDEX_LOAD_RANDOM_ACCESS_FILTERS_EAGERLY_SETTING,
                 IndexModule.INDEX_STORE_TYPE_SETTING,
                 IndexModule.INDEX_STORE_PRE_LOAD_SETTING,
+                IndexModule.INDEX_STORE_HYBRID_MMAP_EXTENSIONS,
                 IndexModule.INDEX_RECOVERY_TYPE_SETTING,
                 IndexModule.INDEX_QUERY_CACHE_ENABLED_SETTING,
                 FsDirectoryFactory.INDEX_LOCK_FACTOR_SETTING,

server/src/main/java/org/opensearch/index/IndexModule.java

@@ -148,6 +148,18 @@ public final class IndexModule {
         Property.NodeScope
     );
 
+    /** Which lucene file extensions to load with the mmap directory when using hybridfs store.
+     *  This is an expert setting.
+     *  @see <a href="https://lucene.apache.org/core/9_2_0/core/org/apache/lucene/codecs/lucene92/package-summary.html#file-names">Lucene File Extensions</a>.
+     */
+    public static final Setting<List<String>> INDEX_STORE_HYBRID_MMAP_EXTENSIONS = Setting.listSetting(
+        "index.store.hybrid.mmap.extensions",
+        List.of("nvd", "dvd", "tim", "tip", "dim", "kdd", "kdi", "cfs", "doc"),
+        Function.identity(),
+        Property.IndexScope,
+        Property.NodeScope
+    );
+
     public static final String SIMILARITY_SETTINGS_PREFIX = "index.similarity";
 
     // whether to use the query cache

server/src/main/java/org/opensearch/index/store/FsDirectoryFactory.java

@@ -97,9 +97,10 @@ protected Directory newFSDirectory(Path location, LockFactory lockFactory, Index
             case HYBRIDFS:
                 // Use Lucene defaults
                 final FSDirectory primaryDirectory = FSDirectory.open(location, lockFactory);
+                final Set<String> mmapExtensions = new HashSet<>(indexSettings.getValue(IndexModule.INDEX_STORE_HYBRID_MMAP_EXTENSIONS));
                 if (primaryDirectory instanceof MMapDirectory) {
                     MMapDirectory mMapDirectory = (MMapDirectory) primaryDirectory;
-                    return new HybridDirectory(lockFactory, setPreload(mMapDirectory, lockFactory, preLoadExtensions));
+                    return new HybridDirectory(lockFactory, setPreload(mMapDirectory, lockFactory, preLoadExtensions), mmapExtensions);
                 } else {
                     return primaryDirectory;
                 }
@@ -142,10 +143,12 @@ public static boolean isHybridFs(Directory directory) {
      */
     static final class HybridDirectory extends NIOFSDirectory {
         private final MMapDirectory delegate;
+        private final Set<String> mmapExtensions;
 
-        HybridDirectory(LockFactory lockFactory, MMapDirectory delegate) throws IOException {
+        HybridDirectory(LockFactory lockFactory, MMapDirectory delegate, Set<String> mmapExtensions) throws IOException {
             super(delegate.getDirectory(), lockFactory);
             this.delegate = delegate;
+            this.mmapExtensions = mmapExtensions;
         }
 
         @Override
@@ -164,43 +167,16 @@ public IndexInput openInput(String name, IOContext context) throws IOException {
             }
         }
 
+        boolean useDelegate(String name) {
+            final String extension = FileSwitchDirectory.getExtension(name);
+            return mmapExtensions.contains(extension);
+        }
+
         @Override
         public void close() throws IOException {
             IOUtils.close(super::close, delegate);
         }
 
-        boolean useDelegate(String name) {
-            String extension = FileSwitchDirectory.getExtension(name);
-            switch (extension) {
-                // Norms, doc values and term dictionaries are typically performance-sensitive and hot in the page
-                // cache, so we use mmap, which provides better performance.
-                case "nvd":
-                case "dvd":
-                case "tim":
-                    // We want to open the terms index and KD-tree index off-heap to save memory, but this only performs
-                    // well if using mmap.
-                case "tip":
-                    // dim files only apply up to lucene 8.x indices. It can be removed once we are in lucene 10
-                case "dim":
-                case "kdd":
-                case "kdi":
-                    // Compound files are tricky because they store all the information for the segment. Benchmarks
-                    // suggested that not mapping them hurts performance.
-                case "cfs":
-                    // MMapDirectory has special logic to read long[] arrays in little-endian order that helps speed
-                    // up the decoding of postings. The same logic applies to positions (.pos) of offsets (.pay) but we
-                    // are not mmaping them as queries that leverage positions are more costly and the decoding of postings
-                    // tends to be less a bottleneck.
-                case "doc":
-                    return true;
-                // Other files are either less performance-sensitive (e.g. stored field index, norms metadata)
-                // or are large and have a random access pattern and mmap leads to page cache trashing
-                // (e.g. stored fields and term vectors).
-                default:
-                    return false;
-            }
-        }
-
         MMapDirectory getDelegate() {
             return delegate;
         }

server/src/test/java/org/opensearch/index/store/FsDirectoryFactoryTests.java

@@ -70,20 +70,52 @@ public void testPreload() throws IOException {
         try (Directory directory = newDirectory(build)) {
             assertTrue(FsDirectoryFactory.isHybridFs(directory));
             FsDirectoryFactory.HybridDirectory hybridDirectory = (FsDirectoryFactory.HybridDirectory) directory;
-            assertTrue(hybridDirectory.useDelegate("foo.dvd"));
+            // test default hybrid mmap extensions
             assertTrue(hybridDirectory.useDelegate("foo.nvd"));
+            assertTrue(hybridDirectory.useDelegate("foo.dvd"));
             assertTrue(hybridDirectory.useDelegate("foo.tim"));
             assertTrue(hybridDirectory.useDelegate("foo.tip"));
-            assertTrue(hybridDirectory.useDelegate("foo.cfs"));
             assertTrue(hybridDirectory.useDelegate("foo.dim"));
             assertTrue(hybridDirectory.useDelegate("foo.kdd"));
             assertTrue(hybridDirectory.useDelegate("foo.kdi"));
-            assertFalse(hybridDirectory.useDelegate("foo.bar"));
+            assertTrue(hybridDirectory.useDelegate("foo.cfs"));
+            assertTrue(hybridDirectory.useDelegate("foo.doc"));
+            assertFalse(hybridDirectory.useDelegate("foo.pos"));
+            assertFalse(hybridDirectory.useDelegate("foo.pay"));
             MMapDirectory delegate = hybridDirectory.getDelegate();
             assertThat(delegate, Matchers.instanceOf(FsDirectoryFactory.PreLoadMMapDirectory.class));
             FsDirectoryFactory.PreLoadMMapDirectory preLoadMMapDirectory = (FsDirectoryFactory.PreLoadMMapDirectory) delegate;
             assertTrue(preLoadMMapDirectory.useDelegate("foo.dvd"));
             assertTrue(preLoadMMapDirectory.useDelegate("foo.bar"));
+            assertFalse(preLoadMMapDirectory.useDelegate("foo.cfs"));
+        }
+        build = Settings.builder()
+            .put(IndexModule.INDEX_STORE_TYPE_SETTING.getKey(), IndexModule.Type.HYBRIDFS.name().toLowerCase(Locale.ROOT))
+            .putList(IndexModule.INDEX_STORE_PRE_LOAD_SETTING.getKey(), "nvd", "dvd", "cfs")
+            .putList(IndexModule.INDEX_STORE_HYBRID_MMAP_EXTENSIONS.getKey(), "nvd", "dvd", "tim", "pos", "pay")
+            .build();
+        try (Directory directory = newDirectory(build)) {
+            assertTrue(FsDirectoryFactory.isHybridFs(directory));
+            FsDirectoryFactory.HybridDirectory hybridDirectory = (FsDirectoryFactory.HybridDirectory) directory;
+            // test custom hybrid mmap extensions
+            assertTrue(hybridDirectory.useDelegate("foo.nvd"));
+            assertTrue(hybridDirectory.useDelegate("foo.dvd"));
+            assertTrue(hybridDirectory.useDelegate("foo.tim"));
+            assertFalse(hybridDirectory.useDelegate("foo.tip"));
+            assertFalse(hybridDirectory.useDelegate("foo.dim"));
+            assertFalse(hybridDirectory.useDelegate("foo.kdd"));
+            assertFalse(hybridDirectory.useDelegate("foo.kdi"));
+            assertFalse(hybridDirectory.useDelegate("foo.cfs"));
+            assertFalse(hybridDirectory.useDelegate("foo.doc"));
+            assertTrue(hybridDirectory.useDelegate("foo.pos"));
+            assertTrue(hybridDirectory.useDelegate("foo.pay"));
+            MMapDirectory delegate = hybridDirectory.getDelegate();
+            assertThat(delegate, Matchers.instanceOf(FsDirectoryFactory.PreLoadMMapDirectory.class));
+            FsDirectoryFactory.PreLoadMMapDirectory preLoadMMapDirectory = (FsDirectoryFactory.PreLoadMMapDirectory) delegate;
+            assertTrue(preLoadMMapDirectory.useDelegate("foo.dvd"));
+            assertFalse(preLoadMMapDirectory.useDelegate("foo.bar"));
+            assertTrue(preLoadMMapDirectory.useDelegate("foo.cfs"));
+            assertTrue(preLoadMMapDirectory.useDelegate("foo.nvd"));
         }
     }