2 files changed, 51 insertions, 12 deletions
diff --git a/src/mongo/db/explain.cpp b/src/mongo/db/explain.cpp
index 89a7f0bef5d..ecfa182f85e 100644
--- a/src/mongo/db/explain.cpp
+++ b/src/mongo/db/explain.cpp
@@ -170,22 +170,18 @@ namespace mongo {
             }
         }
         // Return a plan with the highest match count.
-        // TODO simplify
-        long long maxN = 0;
+        long long maxN = -1;
+        shared_ptr<const ExplainPlanInfo> ret;
         for( list<shared_ptr<const ExplainPlanInfo> >::const_iterator i = _plans.begin();
             i != _plans.end(); ++i ) {
-            if ( (*i)->n() > maxN ) {
-                maxN = (*i)->n();
+            long long n = ( *i )->n();
+            if ( n > maxN ) {
+                maxN = n;
+                ret = *i;
             }
         }
-        for( list<shared_ptr<const ExplainPlanInfo> >::const_iterator i = _plans.begin();
-            i != _plans.end(); ++i ) {
-            if ( (*i)->n() == maxN ) {
-                return **i;
-            }
-        }
-        verify( 16076, false );
-        return *(new ExplainPlanInfo());
+        verify( 16076, ret );
+        return *ret;
     }
     
     void ExplainQueryInfo::noteIterate( bool match, bool loadedObject, bool chunkSkip ) {
diff --git a/src/mongo/dbtests/queryoptimizercursortests.cpp b/src/mongo/dbtests/queryoptimizercursortests.cpp
index 905f1172fa1..c083a863580 100644
--- a/src/mongo/dbtests/queryoptimizercursortests.cpp
+++ b/src/mongo/dbtests/queryoptimizercursortests.cpp
@@ -3891,6 +3891,48 @@ namespace QueryOptimizerCursorTests {
                 ASSERT( clause1[ "indexOnly" ].Bool() );
             }
         };
+        
+        /**
+         * Check that the plan with the most matches is reported at the top of the explain output
+         * in the absence of a done or picked plan.
+         */
+        class VirtualPickedPlan : public Base {
+        public:
+            void run() {
+                dblock lk;
+                Client::Context ctx( ns() );
+                
+                _cli.ensureIndex( ns(), BSON( "a" << 1 ) );
+                _cli.ensureIndex( ns(), BSON( "b" << 1 ) );
+                _cli.ensureIndex( ns(), BSON( "c" << 1 ) );
+                
+                shared_ptr<Cursor> aCursor
+                ( NamespaceDetailsTransient::getCursor( ns(), BSON( "a" << 1 ) ) );
+                shared_ptr<Cursor> bCursor
+                ( NamespaceDetailsTransient::getCursor( ns(), BSON( "b" << 1 ) ) );
+                shared_ptr<Cursor> cCursor
+                ( NamespaceDetailsTransient::getCursor( ns(), BSON( "c" << 1 ) ) );
+                
+                shared_ptr<ExplainPlanInfo> aPlan( new ExplainPlanInfo() );
+                aPlan->notePlan( *aCursor, false, false );
+                shared_ptr<ExplainPlanInfo> bPlan( new ExplainPlanInfo() );
+                bPlan->notePlan( *bCursor, false, false );
+                shared_ptr<ExplainPlanInfo> cPlan( new ExplainPlanInfo() );
+                cPlan->notePlan( *cCursor, false, false );
+                
+                aPlan->noteIterate( true, false, *aCursor ); // one match a
+                bPlan->noteIterate( true, false, *bCursor ); // two matches b
+                bPlan->noteIterate( true, false, *bCursor );
+                cPlan->noteIterate( true, false, *cCursor ); // one match c
+                
+                shared_ptr<ExplainClauseInfo> clause( new ExplainClauseInfo() );
+                clause->addPlanInfo( aPlan );
+                clause->addPlanInfo( bPlan );
+                clause->addPlanInfo( cPlan );
+                
+                ASSERT_EQUALS( "BtreeCursor b_1", clause->bson()[ "cursor" ].String() );
+            }
+        };
 
         // test takeover w/ mixed plan clause ? necessary?
 
@@ -4046,6 +4088,7 @@ namespace QueryOptimizerCursorTests {
             add<Explain::NChunkSkipsTakeover>();
             add<Explain::CoveredIndex>();
             add<Explain::CoveredIndexTakeover>();
+            add<Explain::VirtualPickedPlan>();
         }
     } myall;