SERVER-14097 SERVER-14098 execution-level explain for .find() and .count()

The explain implementation for .find() and .count() is feature complete. To use
the .find() implementation, set the enableNewExplain setParameter to true.

Count operations are explained through the new explain command, e.g.
db.runCommand({explain: {count: "coll", query: {foo: "bar"}}}).

1 files changed, 7 insertions, 0 deletions

diff --git a/src/mongo/db/exec/merge_sort.cpp b/src/mongo/db/exec/merge_sort.cpp
index e35d0570423..6716a4b1c56 100644
--- a/src/mongo/db/exec/merge_sort.cpp
+++ b/src/mongo/db/exec/merge_sort.cpp
@@ -67,6 +67,9 @@ namespace mongo {
     PlanStage::StageState MergeSortStage::work(WorkingSetID* out) {
         ++_commonStats.works;
 
+        // Adds the amount of time taken by work() to executionTimeMillis.
+        ScopedTimer timer(&_commonStats.executionTimeMillis);
+
         if (isEOF()) { return PlanStage::IS_EOF; }
 
         if (!_noResultToMerge.empty()) {
@@ -246,6 +249,10 @@ namespace mongo {
         return false;
     }
 
+    vector<PlanStage*> MergeSortStage::getChildren() const {
+        return _children;
+    }
+
     PlanStageStats* MergeSortStage::getStats() {
         _commonStats.isEOF = isEOF();