1 files changed, 28 insertions, 5 deletions
diff --git a/src/mongo/db/ops/count.cpp b/src/mongo/db/ops/count.cpp
index 713c40edb5a..c63b4e5d8c6 100644
--- a/src/mongo/db/ops/count.cpp
+++ b/src/mongo/db/ops/count.cpp
@@ -26,6 +26,33 @@
 #include "mongo/util/elapsed_tracker.h"
 
 namespace mongo {
+
+    namespace {
+
+        /**
+         * Specialized Cursor creation rules that the count operator provides to the query
+         * processing system.  These rules limit the performance overhead when counting index keys
+         * matching simple predicates.  See SERVER-1752.
+         */
+        class CountPlanPolicies : public QueryPlanSelectionPolicy {
+
+            virtual string name() const { return "CountPlanPolicies"; }
+
+            virtual bool requestMatcher() const {
+                // Avoid using a Matcher when a Cursor will exactly match a query.
+                return false;
+            }
+
+            virtual bool requestIntervalCursor() const {
+                // Request use of an IntervalBtreeCursor when the index bounds represent a single
+                // btree interval.  This Cursor implementation is optimized for performing counts
+                // between two endpoints.
+                return true;
+            }
+
+        } _countPlanPolicies;
+
+    }
     
     long long runCount( const char *ns, const BSONObj &cmd, string &err, int &errCode ) {
         Client::Context cx(ns);
@@ -53,11 +80,7 @@ namespace mongo {
                 NamespaceDetailsTransient::getCursor( ns,
                                                       query,
                                                       BSONObj(),
-                                                      QueryPlanSelectionPolicy::any(),
-                                                      // Avoid using a Matcher when a Cursor can
-                                                      // exactly match the query using a
-                                                      // FieldRangeVector.  See SERVER-1752.
-                                                      false /* requestMatcher */ );
+                                                      _countPlanPolicies );
         ClientCursor::Holder ccPointer;
         ElapsedTracker timeToStartYielding( 256, 20 );
         try {