LUCENE-2060: change CMS's default maxThreadCount from 3 to 1

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@836155 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -40,6 +40,13 @@ Changes in runtime behavior
   fields when reading. You have to reindex to do that.
   (Michael Busch, Uwe Schindler)
 
+ * LUCENE-2060: Chagned ConcurrentMergeScheduler's default for
+   maxNumThreads from 3 to 1, because in practice we get the most
+   gains from running a single merge in the backround.  More than one
+   concurrent merge causes alot of thrashing (though it's possible on
+   SSD storage that there would be net gains).  (Jason Rutherglen,
+   Mike McCandless)
+
 API Changes
 
 * LUCENE-1257, LUCENE-1984, LUCENE-1985, LUCENE-2057,...: Port to Java 1.5

src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java

@@ -39,7 +39,7 @@ public class ConcurrentMergeScheduler extends MergeScheduler {
   protected List<MergeThread> mergeThreads = new ArrayList<MergeThread>();
 
   // Max number of threads allowed to be merging at once
-  private int maxThreadCount = 3;
+  private int maxThreadCount = 1;
 
   protected Directory dir;