Index: CHANGES.txt
===================================================================
--- CHANGES.txt	(revision 722053)
+++ CHANGES.txt	(working copy)
@@ -105,6 +105,10 @@
     slower first-time usage due to populating the FieldCache.  (Tim
     Sturge via Mike McCandless)
 
+ 8. LUCENE-1296: add protected method CachingWrapperFilter.docIdSetToCache 
+    to allow subclasses to choose which DocIdSet implementation to use
+    (Paul Elschot via Mike McCandless)
+
 Optimizations
 
  1. LUCENE-1427: Fixed QueryWrapperFilter to not waste time computing
Index: src/java/org/apache/lucene/search/CachingWrapperFilter.java
===================================================================
--- src/java/org/apache/lucene/search/CachingWrapperFilter.java	(revision 722053)
+++ src/java/org/apache/lucene/search/CachingWrapperFilter.java	(working copy)
@@ -73,6 +73,14 @@
 
     return bits;
   }
+
+  /** Provide the DocIdSet to be cached, using the DocIdSet provided
+   *  by the wrapped Filter.
+   *  This implementation returns the given DocIdSet.
+   */
+  protected DocIdSet docIdSetToCache(DocIdSet docIdSet, IndexReader reader) {
+    return docIdSet;
+  }
   
   public DocIdSet getDocIdSet(IndexReader reader) throws IOException {
     if (cache == null) {
@@ -91,7 +99,7 @@
         return new DocIdBitSet((BitSet) cached);
     }
 
-    final DocIdSet docIdSet = filter.getDocIdSet(reader);
+    final DocIdSet docIdSet = docIdSetToCache(filter.getDocIdSet(reader), reader);
 
     synchronized (cache) {  // update cache
       cache.put(reader, docIdSet);
Index: contrib/miscellaneous/src/java/org/apache/lucene/misc/ChainedFilter.java
===================================================================
--- contrib/miscellaneous/src/java/org/apache/lucene/misc/ChainedFilter.java	(revision 722055)
+++ contrib/miscellaneous/src/java/org/apache/lucene/misc/ChainedFilter.java	(working copy)
@@ -177,7 +177,10 @@
         return result;
     }
     
-    /** Provide a SortedVIntList when it is definitely smaller than an OpenBitSet */
+    /** Provide a SortedVIntList when it is definitely
+     *  smaller than an OpenBitSet
+     *  @deprecated Either use CachingWrapperFilter, or
+     *  switch to a different DocIdSet implementation yourself. */
     protected DocIdSet finalResult(OpenBitSetDISI result, int maxDocs) {
         return (result.cardinality() < (maxDocs / 9))
               ? (DocIdSet) new SortedVIntList(result)
Index: contrib/queries/src/java/org/apache/lucene/search/BooleanFilter.java
===================================================================
--- contrib/queries/src/java/org/apache/lucene/search/BooleanFilter.java	(revision 722055)
+++ contrib/queries/src/java/org/apache/lucene/search/BooleanFilter.java	(working copy)
@@ -116,7 +116,10 @@
     return emptyDocIdSet;
   }
 
-  /** Provide a SortedVIntList when it is definitely smaller than an OpenBitSet */
+  /** Provide a SortedVIntList when it is definitely smaller
+   * than an OpenBitSet.
+   * @deprecated Either use CachingWrapperFilter, or
+   * switch to a different DocIdSet implementation yourself. */
   protected DocIdSet finalResult(OpenBitSetDISI result, int maxDocs) {
     return (result.cardinality() < (maxDocs / 9))
       ? (DocIdSet) new SortedVIntList(result)