SERVER-29421 Make agg explain use outer PlanExecutor

1 files changed, 73 insertions, 19 deletions

diff --git a/src/mongo/db/query/explain.h b/src/mongo/db/query/explain.h
index 8202cbfbeec..cb177321f1c 100644
--- a/src/mongo/db/query/explain.h
+++ b/src/mongo/db/query/explain.h
@@ -59,6 +59,9 @@ public:
      *
      * Does not take ownership of its arguments.
      *
+     * The caller should hold at least an IS lock on the collection the that the query runs on,
+     * even if 'collection' is nullptr.
+     *
      * If there is an error during the execution of the query, the error message and code are
      * added to the "executionStats" section of the explain.
      */
@@ -66,6 +69,37 @@ public:
                               const Collection* collection,
                               ExplainOptions::Verbosity verbosity,
                               BSONObjBuilder* out);
+    /**
+     * Adds "queryPlanner" and "executionStats" (if requested in verbosity) fields to 'out'. Unlike
+     * the other overload of explainStages() above, this one does not add the "serverInfo" section.
+     *
+     * - 'exec' is the stage tree for the operation being explained.
+     * - 'collection' is the relevant collection. The caller should hold at least an IS lock on the
+     * collection which the query ran on, even 'collection' is nullptr.
+     * - 'verbosity' is the verbosity level of the explain.
+     * - 'executePlanStatus' is the status returned after executing the query (Status::OK if the
+     * query wasn't executed).
+     * - 'winningPlanTrialStats' is the stats of the winning plan during the trial period. May be
+     * nullptr.
+     * - 'out' is the builder for the explain output.
+     **/
+    static void explainStages(PlanExecutor* exec,
+                              const Collection* collection,
+                              ExplainOptions::Verbosity verbosity,
+                              Status executePlanStatus,
+                              PlanStageStats* winningPlanTrialStats,
+                              BSONObjBuilder* out);
+
+    /**
+     * Gets explain BSON for the document sources contained by 'exec'. Use this function if you
+     * have a PlanExecutor whose root is a PipelineProxyStage and want to turn it into a human
+     * readable explain format.
+     *
+     * The explain information is generated with the level of detail specified by 'verbosity'.
+     **/
+    static void explainPipelineExecutor(PlanExecutor* exec,
+                                        ExplainOptions::Verbosity verbosity,
+                                        BSONObjBuilder* out);
 
     /**
      * Converts the PlanExecutor's winning plan stats tree to BSON and returns to the caller.
@@ -122,8 +156,31 @@ public:
      */
     static void getSummaryStats(const PlanExecutor& exec, PlanSummaryStats* statsOut);
 
+    /**
+     * If exec's root stage is a MultiPlanStage, returns the stats for the trial period of of the
+     * winning plan. Otherwise, returns nullptr.
+     *
+     * Must be called _before_ calling PlanExecutor::executePlan() or PlanExecutor::getNext().
+     **/
+    static std::unique_ptr<PlanStageStats> getWinningPlanTrialStats(PlanExecutor* exec);
+
 private:
     /**
+     * Adds the 'queryPlanner' explain section to the BSON object being built
+     * by 'out'.
+     *
+     * This is a helper for generating explain BSON. It is used by explainStages(...).
+     *
+     * - 'exec' is the stage tree for the operation being explained.
+     * - 'collection' is the collection used in the operation. The caller should hold an IS lock on
+     * the collection which the query is for, even if 'collection' is nullptr.
+     * - 'out' is a builder for the explain output.
+     */
+    static void generatePlannerInfo(PlanExecutor* exec,
+                                    const Collection* collection,
+                                    BSONObjBuilder* out);
+
+    /**
      * Private helper that does the heavy-lifting for the public statsToBSON(...) functions
      * declared above.
      *
@@ -135,22 +192,19 @@ private:
                             BSONObjBuilder* topLevelBob);
 
     /**
-     * Adds the 'queryPlanner' explain section to the BSON object being built
-     * by 'out'.
+     * Adds the "executionStats" field to out. Assumes PlanExecutor::executePlan() has been called
+     * and that verbosity >= kExecStats.
      *
-     * This is a helper for generating explain BSON. It is used by explainStages(...).
+     * If verbosity >= kExecAllPlans, it will include the "allPlansExecution" array.
      *
-     * @param exec -- the stage tree for the operation being explained.
-     * @param collection -- the collection used in the operation.
-     * @param winnerStats -- the stats tree for the winning plan.
-     * @param rejectedStats -- an array of stats trees, one per rejected plan
-     */
-    static void generatePlannerInfo(
-        PlanExecutor* exec,
-        const Collection* collection,
-        PlanStageStats* winnerStats,
-        const std::vector<std::unique_ptr<PlanStageStats>>& rejectedStats,
-        BSONObjBuilder* out);
+     * - 'execPlanStatus' is the value returned after executing the query.
+     * - 'winningPlanTrialStats' may be nullptr.
+     **/
+    static void generateExecutionInfo(PlanExecutor* exec,
+                                      ExplainOptions::Verbosity verbosity,
+                                      Status executePlanStatus,
+                                      PlanStageStats* winningPlanTrialStats,
+                                      BSONObjBuilder* out);
 
     /**
      * Generates the execution stats section for the stats tree 'stats',
@@ -163,12 +217,12 @@ private:
      *
      * Stats are generated at the verbosity specified by 'verbosity'.
      *
-     * This is a helper for generating explain BSON. It is used by explainStages(...).
+     * This is a helper for generating explain BSON. It is used by generateExecutionInfo().
      */
-    static void generateExecStats(PlanStageStats* stats,
-                                  ExplainOptions::Verbosity verbosity,
-                                  BSONObjBuilder* out,
-                                  boost::optional<long long> totalTimeMillis);
+    static void generateSinglePlanExecutionInfo(const PlanStageStats* stats,
+                                                ExplainOptions::Verbosity verbosity,
+                                                boost::optional<long long> totalTimeMillis,
+                                                BSONObjBuilder* out);
 
     /**
      * Adds the 'serverInfo' explain section to the BSON object being build