Allow Lucene directory implementations to estimate their size (#97822)

This change introduces a ByteSizeDirectory abstract class that can be 
implemented to expose an estimate of the directory files size in the 
store stats.

It allows plugins with custom Lucene directory implementation to 
extend this class and expose their own estimate of the directory size.

Relates ES-5995

docs/changelog/97822.yaml

@@ -0,0 +1,5 @@
+pr: 97822
+summary: Allow Lucene directory implementations to estimate their size
+area: Store
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/index/store/ByteSizeCachingDirectory.java

@@ -9,7 +9,6 @@
 package org.elasticsearch.index.store;
 
 import org.apache.lucene.store.Directory;
-import org.apache.lucene.store.FilterDirectory;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexOutput;
 import org.elasticsearch.common.lucene.store.FilterIndexOutput;
@@ -22,7 +21,7 @@ import java.io.UncheckedIOException;
 import java.nio.file.AccessDeniedException;
 import java.nio.file.NoSuchFileException;
 
-final class ByteSizeCachingDirectory extends FilterDirectory {
+final class ByteSizeCachingDirectory extends ByteSizeDirectory {
 
     private static class SizeAndModCount {
         final long size;
@@ -57,7 +56,7 @@ final class ByteSizeCachingDirectory extends FilterDirectory {
 
     ByteSizeCachingDirectory(Directory in, TimeValue refreshInterval) {
         super(in);
-        size = new SingleObjectCache<SizeAndModCount>(refreshInterval, new SizeAndModCount(0L, -1L, true)) {
+        size = new SingleObjectCache<>(refreshInterval, new SizeAndModCount(0L, -1L, true)) {
             @Override
             protected SizeAndModCount refresh() {
                 // It is ok for the size of the directory to be more recent than
@@ -103,8 +102,8 @@ final class ByteSizeCachingDirectory extends FilterDirectory {
         };
     }
 
-    /** Return the cumulative size of all files in this directory. */
-    long estimateSizeInBytes() throws IOException {
+    @Override
+    public long estimateSizeInBytes() throws IOException {
         try {
             return size.getOrRefresh().size;
         } catch (UncheckedIOException e) {

server/src/main/java/org/elasticsearch/index/store/ByteSizeDirectory.java

@@ -0,0 +1,24 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.index.store;
+
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.FilterDirectory;
+
+import java.io.IOException;
+
+public abstract class ByteSizeDirectory extends FilterDirectory {
+
+    protected ByteSizeDirectory(Directory in) {
+        super(in);
+    }
+
+    /** Return the cumulative size of all files in this directory. */
+    public abstract long estimateSizeInBytes() throws IOException;
+}

server/src/main/java/org/elasticsearch/index/store/Store.java

@@ -27,7 +27,6 @@ import org.apache.lucene.store.BufferedChecksum;
 import org.apache.lucene.store.ByteArrayDataInput;
 import org.apache.lucene.store.ChecksumIndexInput;
 import org.apache.lucene.store.Directory;
-import org.apache.lucene.store.FilterDirectory;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.store.IndexOutput;
@@ -162,10 +161,10 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
 
     public Store(ShardId shardId, IndexSettings indexSettings, Directory directory, ShardLock shardLock, OnClose onClose) {
         super(shardId, indexSettings);
-        final TimeValue refreshInterval = indexSettings.getValue(INDEX_STORE_STATS_REFRESH_INTERVAL_SETTING);
-        logger.debug("store stats are refreshed with refresh_interval [{}]", refreshInterval);
-        ByteSizeCachingDirectory sizeCachingDir = new ByteSizeCachingDirectory(directory, refreshInterval);
-        this.directory = new StoreDirectory(sizeCachingDir, Loggers.getLogger("index.store.deletes", shardId));
+        this.directory = new StoreDirectory(
+            byteSizeDirectory(directory, indexSettings, logger),
+            Loggers.getLogger("index.store.deletes", shardId)
+        );
         this.shardLock = shardLock;
         this.onClose = onClose;
 
@@ -355,7 +354,7 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
      */
     public StoreStats stats(long reservedBytes, LongUnaryOperator localSizeFunction) throws IOException {
         ensureOpen();
-        long sizeInBytes = directory.estimateSize();
+        long sizeInBytes = directory.estimateSizeInBytes();
         return new StoreStats(localSizeFunction.applyAsLong(sizeInBytes), sizeInBytes, reservedBytes);
     }
 
@@ -443,6 +442,16 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
         }
     }
 
+    private static ByteSizeDirectory byteSizeDirectory(Directory directory, IndexSettings indexSettings, Logger logger) {
+        if (directory instanceof ByteSizeDirectory byteSizeDirectory) {
+            return byteSizeDirectory;
+        } else {
+            final TimeValue refreshInterval = indexSettings.getValue(INDEX_STORE_STATS_REFRESH_INTERVAL_SETTING);
+            logger.debug("store stats are refreshed with {} [{}]", INDEX_STORE_STATS_REFRESH_INTERVAL_SETTING.getKey(), refreshInterval);
+            return new ByteSizeCachingDirectory(directory, refreshInterval);
+        }
+    }
+
     /**
      * Reads a MetadataSnapshot from the given index locations or returns an empty snapshot if it can't be read.
      *
@@ -720,18 +729,18 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
         shardLock.setDetails("closing shard");
     }
 
-    static final class StoreDirectory extends FilterDirectory {
+    static final class StoreDirectory extends ByteSizeDirectory {
 
         private final Logger deletesLogger;
 
-        StoreDirectory(ByteSizeCachingDirectory delegateDirectory, Logger deletesLogger) {
+        StoreDirectory(ByteSizeDirectory delegateDirectory, Logger deletesLogger) {
             super(delegateDirectory);
             this.deletesLogger = deletesLogger;
         }
 
-        /** Estimate the cumulative size of all files in this directory in bytes. */
-        long estimateSize() throws IOException {
-            return ((ByteSizeCachingDirectory) getDelegate()).estimateSizeInBytes();
+        @Override
+        public long estimateSizeInBytes() throws IOException {
+            return ((ByteSizeDirectory) getDelegate()).estimateSizeInBytes();
         }
 
         @Override