[GitHub] [lucene] mikemccand commented on a diff in pull request #11796: GITHUB#11795: Add FilterDirectory to track write amplification factor

[GitBox <gi...@apache.org>]

mikemccand commented on code in PR #11796:
URL: https://github.com/apache/lucene/pull/11796#discussion_r977831498


##########
lucene/core/src/java/org/apache/lucene/store/ByteTrackingIndexOutput.java:
##########
@@ -0,0 +1,70 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.store;
+
+import java.io.IOException;
+import java.util.concurrent.atomic.AtomicLong;
+
+/** An {@link IndexOutput} that wraps another instance and tracks the number of bytes written */
+public class ByteTrackingIndexOutput extends IndexOutput {
+
+  private final IndexOutput output;
+  private final AtomicLong byteTracker;
+
+  protected ByteTrackingIndexOutput(IndexOutput output, AtomicLong byteTracker) {
+    super(
+        "Byte tracking wrapper for: " + output.getName(),
+        "ByteTrackingIndexOutput{" + output.getName() + "}");
+    this.output = output;
+    this.byteTracker = byteTracker;
+  }
+
+  @Override
+  public void writeByte(byte b) throws IOException {
+    byteTracker.incrementAndGet();
+    output.writeByte(b);
+  }
+
+  @Override
+  public void writeBytes(byte[] b, int offset, int length) throws IOException {
+    byteTracker.addAndGet(length);
+    output.writeBytes(b, offset, length);
+  }
+
+  @Override
+  public void close() throws IOException {

Review Comment:
   Maybe we can separately add a proper / tested delegator, `FilterIndexOutput`.  Lucene has a number of these delegator classes (`FilterXXX`) but not yet `FilterIndexOutput`.  Elasticsearch seems to have one... but if you poach/borrow from there make sure to use the 7.10 or earlier version that is still Apache Software License.



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