SERVER-10026 stage stats, multi plan runner, relevant scaffolding

1 files changed, 78 insertions, 0 deletions

diff --git a/src/mongo/db/query/plan_ranker.h b/src/mongo/db/query/plan_ranker.h
new file mode 100644
index 00000000000..e4a980a713d
--- /dev/null
+++ b/src/mongo/db/query/plan_ranker.h
@@ -0,0 +1,78 @@
+/**
+ *    Copyright (C) 2013 10gen Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <queue>
+#include <vector>
+
+#include "mongo/db/exec/plan_stage.h"
+#include "mongo/db/exec/plan_stats.h"
+#include "mongo/db/exec/working_set.h"
+#include "mongo/db/query/query_solution.h"
+
+namespace mongo {
+
+    struct CandidatePlan;
+    struct PlanRankingDecision;
+
+    /**
+     * Ranks 2 or more plans.
+     */
+    class PlanRanker {
+    public:
+        /**
+         * Returns index in 'candidates' of which plan is best.
+         * If 'why' is not NULL, populates it with information relevant to why that plan was picked.
+         */
+        static size_t pickBestPlan(const vector<CandidatePlan>& candidates,
+                                   PlanRankingDecision* why);
+    private:
+        /**
+         * Assign the stats tree a 'goodness' score.  Used internally.
+         */
+        static double scoreTree(const PlanStageStats& stats);
+    };
+
+    /**
+     * A container holding one to-be-ranked plan and its associated/relevant data.
+     * Does not own any of its pointers.
+     */
+    struct CandidatePlan {
+        CandidatePlan(QuerySolution* s, PlanStage* r, WorkingSet* w)
+            : solution(s), root(r), ws(w) { }
+
+        QuerySolution* solution;
+        PlanStage* root;
+        WorkingSet* ws;
+
+        // Any results produced during the plan's execution prior to ranking are retained here.
+        std::queue<WorkingSetID> results;
+    };
+
+    /**
+     * Information about why a plan was picked to be the best.  Data here is placed into the cache
+     * and used by the CachedPlanRunner to compare expected performance with actual.
+     */
+    struct PlanRankingDecision {
+        // Owned by us.
+        PlanStageStats* statsOfWinner;
+
+        // TODO: We can place anything we want here.  What's useful to the cache?  What's useful to
+        // planning and optimization?
+    };
+
+}  // namespace mongo