LUCENE-5668: fix ob1 in TieredMergePolicy

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1594059 13f79535-47bb-0310-9956-ffa450edef68

lucene/CHANGES.txt

@@ -186,6 +186,8 @@ Bug fixes
 * LUCENE-5660: AnalyzingSuggester.build will now throw IllegalArgumentException if
   you give it a longer suggestion than it can handle (Robert Muir, Mike McCandless)
 
+* LUCENE-5668: Fix off-by-one in TieredMergePolicy (Mike McCandless)
+
 Test Framework
 
 * LUCENE-5622: Fail tests if they print over the given limit of bytes to 

lucene/core/src/test/org/apache/lucene/index/TestTieredMergePolicy.java

@@ -211,4 +211,31 @@ public class TestTieredMergePolicy extends BaseMergePolicyTestCase {
     
     // TODO: Add more checks for other non-double setters!
   }
+
+  // LUCENE-5668
+  public void testUnbalancedMergeSelection() throws Exception {
+    Directory dir = newDirectory();
+    IndexWriterConfig iwc = new IndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random()));
+    TieredMergePolicy tmp = (TieredMergePolicy) iwc.getMergePolicy();
+    tmp.setFloorSegmentMB(0.00001);
+    iwc.setMergeScheduler(new SerialMergeScheduler());
+    iwc.setMaxBufferedDocs(100);
+    iwc.setRAMBufferSizeMB(-1);
+    IndexWriter w = new IndexWriter(dir, iwc);
+    for(int i=0;i<100000;i++) {
+      Document doc = new Document();
+      doc.add(newTextField("id", random().nextLong() + "" + random().nextLong(), Field.Store.YES));
+      w.addDocument(doc);
+    }
+    IndexReader r = DirectoryReader.open(w, true);
+
+    // Make sure TMP always merged equal-number-of-docs segments:
+    for(AtomicReaderContext ctx : r.leaves()) {
+      int numDocs = ctx.reader().numDocs();
+      assertTrue("got numDocs=" + numDocs, numDocs == 100 || numDocs == 1000 || numDocs == 10000);
+    }
+    r.close();
+    w.close();
+    dir.close();
+  }
 }