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, 16 insertions, 4 deletions

diff --git a/src/mongo/db/exec/projection.cpp b/src/mongo/db/exec/projection.cpp
index 60c0aa221f3..c4c8388462f 100644
--- a/src/mongo/db/exec/projection.cpp
+++ b/src/mongo/db/exec/projection.cpp
@@ -50,6 +50,8 @@ namespace mongo {
           _commonStats(kStageType),
           _projImpl(params.projImpl) {
 
+        _projObj = params.projObj;
+
         if (ProjectionStageParams::NO_FAST_PATH == _projImpl) {
             _exec.reset(new ProjectionExec(params.projObj, 
                                            params.fullExpression,
@@ -59,8 +61,6 @@ namespace mongo {
             // We shouldn't need the full expression if we're fast-pathing.
             invariant(NULL == params.fullExpression);
 
-            _projObj = params.projObj;
-
             // Sanity-check the input.
             invariant(_projObj.isOwned());
             invariant(!_projObj.isEmpty());
@@ -197,6 +197,9 @@ namespace mongo {
     PlanStage::StageState ProjectionStage::work(WorkingSetID* out) {
         ++_commonStats.works;
 
+        // Adds the amount of time taken by work() to executionTimeMillis.
+        ScopedTimer timer(&_commonStats.executionTimeMillis);
+
         WorkingSetID id = WorkingSet::INVALID_ID;
         StageState status = _child->work(&id);
 
@@ -247,11 +250,20 @@ namespace mongo {
         _child->invalidate(dl, type);
     }
 
+    vector<PlanStage*> ProjectionStage::getChildren() const {
+        vector<PlanStage*> children;
+        children.push_back(_child.get());
+        return children;
+    }
+
     PlanStageStats* ProjectionStage::getStats() {
         _commonStats.isEOF = isEOF();
-        _specificStats.projObj = _projObj;
         auto_ptr<PlanStageStats> ret(new PlanStageStats(_commonStats, STAGE_PROJECTION));
-        ret->specific.reset(new ProjectionStats(_specificStats));
+
+        ProjectionStats* projStats = new ProjectionStats(_specificStats);
+        projStats->projObj = _projObj;
+        ret->specific.reset(projStats);
+
         ret->children.push_back(_child->getStats());
         return ret.release();
     }