[GitHub] [lucene-solr] dsmiley commented on a change in pull request #856: LUCENE-8965 SometimesConcurrentMergeScheduler

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dsmiley commented on a change in pull request #856: LUCENE-8965 SometimesConcurrentMergeScheduler
URL: https://github.com/apache/lucene-solr/pull/856#discussion_r328342889
 
 

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 File path: lucene/core/src/java/org/apache/lucene/index/SometimesConcurrentMergeScheduler.java
 ##########
 @@ -0,0 +1,147 @@
+/*
+ * 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.Observable;
+import java.util.Observer;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.lucene.util.ThreadInterruptedException;
+
+/**
+ * A variant of CMS: If there are cheap merges, wait for a merge to complete before continuing. This
+ * has the benefit of greatly increasing the odds that an {@link org.apache.lucene.search.IndexSearcher}
+ * will see fewer segments. Normally, CMS does all merges concurrently, and so it won't be until the
+ * next commit that the IndexSearcher benefits from fewer segments. The trade-off is less
+ * concurrency, and there will be some delay on a segment flush for a cheap merge if present.
+ *
+ * @author dsmiley
+ * @since solr.7
 
 Review comment:
   Whoops; it was a mistake that I left this when copying from internal work.  Different coding practices.

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