1 files changed, 44 insertions, 0 deletions
diff --git a/jstests/querySystemMigration/queryoptimizer4.js b/jstests/querySystemMigration/queryoptimizer4.js
new file mode 100644
index 00000000000..f83bc82f72a
--- /dev/null
+++ b/jstests/querySystemMigration/queryoptimizer4.js
@@ -0,0 +1,44 @@
+// Check that a new plan will be selected if a recorded plan performs poorly.
+
+t = db.jstests_queryoptimizer4;
+
+function reset( matches, filler ) {
+    t.drop();
+    
+    t.ensureIndex({a:1});
+    t.ensureIndex({b:1});
+    
+    // {a:1} index best for query {a:1,b:1}
+    t.save({a:1,b:1});
+    t.save({a:2,b:1});
+    
+    // {b:1} index best for query {a:100,b:100}
+    for( i = 0; i < matches; ++i ) {
+        t.save({a:100,b:100});        
+    }
+    for( i = 0; i < filler; ++i ) {
+        t.save({a:100,b:5});
+    }
+}
+
+function checkCursor( query, cursor ) {
+    t.find(query).itcount();
+    // Check that index on 'cursor' was chosen in the above query.
+    var x = t.find(query).explain(true);
+    assert.eq( 'BtreeCursor ' + cursor, x.oldPlan.cursor , tojson(x) );    
+}
+
+// Check {b:1} takes over when {a:1} is much worse for query {a:100,b:100}.
+reset( 1, 50 );
+checkCursor( {a:1,b:1}, 'a_1' );
+checkCursor( {a:100,b:100}, 'b_1' );
+
+// Check smallest filler for which {b:1} will take over.
+reset( 2, 12 );
+checkCursor( {a:1,b:1}, 'a_1' );
+checkCursor( {a:100,b:100}, 'b_1' );
+
+// Check largest filler for which {b:1} will not take over - demonstrating that new plans run alongside the old plan.
+reset( 2, 11 );
+checkCursor( {a:1,b:1}, 'a_1' );
+checkCursor( {a:100,b:100}, 'a_1' );