SERVER-10026 fix qlog to be faster

Author: Hari Khalsa

src/mongo/db/query/qlog.cpp

@@ -34,13 +34,6 @@ namespace mongo {
 
     MONGO_EXPORT_SERVER_PARAMETER(verboseQueryLogging, bool, false);
 
-    class nullstream : public std::ostream {
-    public:
-        nullstream() : std::ios(0), std::ostream(0) { }
-    };
-
-    static nullstream theNullStream;
-
     bool qlogOff() {
         bool old = verboseQueryLogging;
         verboseQueryLogging = false;
@@ -53,14 +46,4 @@ namespace mongo {
         return old;
     }
 
-    std::ostream& QLOG() {
-        if (verboseQueryLogging) {
-            return std::cout;
-        }
-        else {
-            return theNullStream;
-        }
-    }
-
 }  // namespace mongo
-

src/mongo/db/query/qlog.h

@@ -32,7 +32,10 @@
 
 namespace mongo {
 
-    std::ostream& QLOG();
+    extern bool verboseQueryLogging;
+
+// With a #define like this, we don't evaluate the costly toString()s that are QLOG'd
+#define QLOG() if (verboseQueryLogging) log()
 
     bool qlogOff();
     bool qlogOn();

src/mongo/db/query/query_planner.h

@@ -55,7 +55,7 @@ namespace mongo {
             INCLUDE_SHARD_FILTER = 4,
 
             // Set this if you don't want any plans with a blocking sort stage.  All sorts must be
-            // provided by the index.
+            // provided by an index.
             NO_BLOCKING_SORT = 8,
         };