Index: src/test/org/apache/lucene/benchmark/byTask/TestPerfTasksLogic.java
===================================================================
--- src/test/org/apache/lucene/benchmark/byTask/TestPerfTasksLogic.java	(revision 956517)
+++ src/test/org/apache/lucene/benchmark/byTask/TestPerfTasksLogic.java	(working copy)
@@ -606,6 +606,40 @@
     }
   }
 
+  public void testDeleteByPercent() throws Exception {
+    // 1. alg definition (required in every "logic" test)
+    String algLines[] = {
+        "# ----- properties ",
+        "content.source=org.apache.lucene.benchmark.byTask.feeds.LineDocSource",
+        "docs.file=" + getReuters20LinesFile(),
+        "ram.flush.mb=-1",
+        "max.buffered=2",
+        "content.source.log.step=3",
+        "doc.term.vector=false",
+        "content.source.forever=false",
+        "directory=RAMDirectory",
+        "doc.stored=false",
+        "doc.tokenized=false",
+        "debug.level=1",
+        "# ----- alg ",
+        "CreateIndex",
+        "{ \"AddDocs\"  AddDoc > : * ",
+        "CloseIndex()",
+        "OpenReader(false)",
+        "DeleteByPercent(20)",
+        "CloseReader"
+    };
+    
+    // 2. execute the algorithm  (required in every "logic" test)
+    Benchmark benchmark = execBenchmark(algLines);
+
+    // 3. test number of docs in the index
+    IndexReader ir = IndexReader.open(benchmark.getRunData().getDirectory(), true);
+    int ndocsExpected = 16; // first 20 reuters docs, minus 20%
+    assertEquals("wrong number of docs in the index!", ndocsExpected, ir.numDocs());
+    ir.close();
+  }
+
   /**
    * Test that we can set merge scheduler".
    */
Index: src/java/org/apache/lucene/benchmark/byTask/tasks/DeleteByPercentTask.java
===================================================================
--- src/java/org/apache/lucene/benchmark/byTask/tasks/DeleteByPercentTask.java	(revision 956517)
+++ src/java/org/apache/lucene/benchmark/byTask/tasks/DeleteByPercentTask.java	(working copy)
@@ -77,10 +77,15 @@
       Bits delDocs = MultiFields.getDeletedDocs(r);
       int doc = 0;
       while (doc < maxDoc && numDeleted < numToDelete) {
-        if (!delDocs.get(doc) && random.nextDouble() <= delRate) {
+        if ((delDocs == null || !delDocs.get(doc)) && random.nextDouble() <= delRate) {
           r.deleteDocument(doc);
           numDeleted++;
+          if (delDocs == null) {
+            delDocs = MultiFields.getDeletedDocs(r);
+            assert delDocs != null;
+          }
         }
+        doc++;
       }
     }
     System.out.println("--> processed (delete) " + numDeleted + " docs");