Index: src/java/org/apache/lucene/search/MultiSearcher.java
===================================================================
--- src/java/org/apache/lucene/search/MultiSearcher.java	(revision 4491)
+++ src/java/org/apache/lucene/search/MultiSearcher.java	(working copy)
@@ -311,6 +311,16 @@
     rewrittenQuery.extractTerms(terms);
 
     // step3
+    final HashMap<Term,Integer> dfMap = createDfMap(terms);
+
+    // step4
+    final int numDocs = maxDoc();
+    final CachedDfSource cacheSim = new CachedDfSource(dfMap, numDocs, getSimilarity());
+
+    return rewrittenQuery.weight(cacheSim);
+  }
+
+  protected HashMap<Term, Integer> createDfMap(Set<Term> terms) throws IOException {
     final Term[] allTermsArray = new Term[terms.size()];
     terms.toArray(allTermsArray);
     int[] aggregatedDfs = new int[terms.size()];
@@ -325,12 +335,7 @@
     for(int i=0; i<allTermsArray.length; i++) {
       dfMap.put(allTermsArray[i], Integer.valueOf(aggregatedDfs[i]));
     }
-
-    // step4
-    final int numDocs = maxDoc();
-    final CachedDfSource cacheSim = new CachedDfSource(dfMap, numDocs, getSimilarity());
-
-    return rewrittenQuery.weight(cacheSim);
+    return dfMap;
   }
 
   /**
Index: src/java/org/apache/lucene/search/ParallelMultiSearcher.java
===================================================================
--- src/java/org/apache/lucene/search/ParallelMultiSearcher.java	(revision 4491)
+++ src/java/org/apache/lucene/search/ParallelMultiSearcher.java	(working copy)
@@ -21,6 +21,8 @@
 import java.util.List;
 import java.util.Arrays;
 import java.util.ArrayList;
+import java.util.Set;
+import java.util.HashMap;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -175,6 +177,39 @@
    }
   }
   
+  @Override
+  protected HashMap<Term, Integer> createDfMap(Set<Term> terms) throws IOException {
+    final Term[] allTermsArray = new Term[terms.size()];
+    terms.toArray(allTermsArray);
+    final int[] aggregatedDfs = new int[terms.size()];
+    
+    @SuppressWarnings("unchecked") final Future<int[]>[] searchThreads = new Future[searchables.length];
+    for (int i = 0; i < searchables.length; i++) {
+      final Searchable searchable = searchables[i];
+      searchThreads[i] = executor.submit(new Callable<int[]>() {
+        public int[] call() throws IOException {
+          return searchable.docFreqs(allTermsArray);
+        }
+      });
+    }
+    foreach(
+      new Function<int[]>() {
+        public void apply(int[] dfs) {
+          for(int j=0; j<aggregatedDfs.length; j++){
+            aggregatedDfs[j] += dfs[j];
+          }
+        }
+      }, 
+      Arrays.asList(searchThreads)
+    );
+
+    final HashMap<Term,Integer> dfMap = new HashMap<Term,Integer>();
+    for(int i=0; i<allTermsArray.length; i++) {
+      dfMap.put(allTermsArray[i], Integer.valueOf(aggregatedDfs[i]));
+    }
+    return dfMap;
+  }
+  
   /*
    * apply the function to each element of the list. This method encapsulates the logic how 
    * to wait for concurrently executed searchables.