mdmarshmallow commented on code in PR #13951:
URL: https://github.com/apache/lucene/pull/13951#discussion_r1815876685


##########
lucene/core/src/java/org/apache/lucene/index/IndexWriterRAMManager.java:
##########
@@ -0,0 +1,116 @@
+/*
+ * 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.index;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * For managing multiple instances of {@link IndexWriter} sharing the same 
buffer (configured by
+ * {@link IndexWriterConfig#setRAMBufferSizeMB})
+ */
+public class IndexWriterRAMManager {
+
+  private final IndexWriterConfig config;
+  private final Map<Integer, IndexWriter> idToWriter = new 
ConcurrentHashMap<>();
+  private final AtomicInteger idGenerator = new AtomicInteger();
+
+  /**
+   * Default constructor
+   *
+   * @param config the index writer config containing the max RAM buffer size
+   */
+  public IndexWriterRAMManager(IndexWriterConfig config) {
+    this.config = config;
+  }
+
+  private int registerWriter(IndexWriter writer) {
+    int id = idGenerator.incrementAndGet();
+    idToWriter.put(id, writer);
+    return id;
+  }
+
+  private void removeWriter(int id) {
+    if (idToWriter.containsKey(id) == false) {
+      throw new IllegalArgumentException(
+          "Writer " + id + " has not been registered or has been removed 
already");
+    }
+    idToWriter.remove(id);
+  }
+
+  private void flushIfNecessary(int id) throws IOException {
+    if (idToWriter.containsKey(id) == false) {
+      throw new IllegalArgumentException(
+          "Writer " + id + " has not been registered or has been removed 
already");
+    }
+    long totalRam = 0L;
+    for (IndexWriter writer : idToWriter.values()) {
+      totalRam += writer.ramBytesUsed();
+    }
+    if (totalRam >= config.getRAMBufferSizeMB() * 1024 * 1024) {
+      IndexWriter writerToFlush = chooseWriterToFlush(idToWriter.values(), 
idToWriter.get(id));
+      writerToFlush.flushNextBuffer();
+    }
+  }
+
+  /**
+   * Chooses which writer should be flushed. Default implementation chooses 
the writer with most RAM
+   * usage

Review Comment:
   Hmm that's interesting! I can make that the default implementation then



##########
lucene/core/src/java/org/apache/lucene/index/IndexWriterRAMManager.java:
##########
@@ -0,0 +1,116 @@
+/*
+ * 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.index;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * For managing multiple instances of {@link IndexWriter} sharing the same 
buffer (configured by
+ * {@link IndexWriterConfig#setRAMBufferSizeMB})

Review Comment:
   Sorry I'm probably missing something here - so I get what you're saying 
about having the `IndexWriterRAMManager` in the `IndexWriterConfig`, but what 
would be the point of creating an `IndexWriterRAMManager` for a single 
`IndexWriter`? Wouldn't `DocumentWriterFlushControl` be sufficient for this 
case?



##########
lucene/core/src/java/org/apache/lucene/index/IndexWriter.java:
##########
@@ -939,11 +941,14 @@ protected final void ensureOpen() throws 
AlreadyClosedException {
    * @param d the index directory. The index is either created or appended 
according <code>
    *     conf.getOpenMode()</code>.
    * @param conf the configuration settings according to which IndexWriter 
should be initialized.
+   * @param indexWriterRAMManager The RAM manager used for multi-tenant RAM 
management
    * @throws IOException if the directory cannot be read/written to, or if it 
does not exist and
    *     <code>conf.getOpenMode()</code> is <code>OpenMode.APPEND</code> or if 
there is any other
    *     low-level IO error
    */
-  public IndexWriter(Directory d, IndexWriterConfig conf) throws IOException {
+  public IndexWriter(
+      Directory d, IndexWriterConfig conf, IndexWriterRAMManager 
indexWriterRAMManager)

Review Comment:
   Sure that makes sense to me



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