1 files changed, 15 insertions, 4 deletions

diff --git a/src/mongo/db/exec/multi_plan.h b/src/mongo/db/exec/multi_plan.h
index 964d71443d0..956969eb2d2 100644
--- a/src/mongo/db/exec/multi_plan.h
+++ b/src/mongo/db/exec/multi_plan.h
@@ -36,6 +36,7 @@
 #include "mongo/db/query/canonical_query.h"
 #include "mongo/db/query/query_solution.h"
 #include "mongo/db/query/plan_ranker.h"
+#include "mongo/db/query/plan_yield_policy.h"
 
 namespace mongo {
 
@@ -81,9 +82,15 @@ namespace mongo {
 
         /**
          * Runs all plans added by addPlan, ranks them, and picks a best.
-         * All further calls to getNext(...) will return results from the best plan.
+         * All further calls to work(...) will return results from the best plan.
+         *
+         * If 'yieldPolicy' is non-NULL, then all locks may be yielded in between round-robin
+         * works of the candidate plans. By default, 'yieldPolicy' is NULL and no yielding will
+         * take place.
+         *
+         * Returns a non-OK status if the plan was killed during yield.
          */
-        void pickBestPlan();
+        Status pickBestPlan(PlanYieldPolicy* yieldPolicy);
 
         /** Return true if a best plan has been chosen  */
         bool bestPlanChosen() const;
@@ -156,20 +163,24 @@ namespace mongo {
         // uses -1 / kNoSuchPlan when best plan is not (yet) known
         int _backupPlanIdx;
 
-        // Did all plans fail while we were running them?  Note that one plan can fail
+        // Set if this MultiPlanStage cannot continue, and the query must fail. This can happen in
+        // two ways. The first is that all candidate plans fail. Note that one plan can fail
         // during normal execution of the plan competition.  Here is an example:
         //
         // Plan 1: collection scan with sort.  Sort runs out of memory.
         // Plan 2: ixscan that provides sort.  Won't run out of memory.
         //
         // We want to choose plan 2 even if plan 1 fails.
+        //
+        // The second way for failure to occur is that the execution of this query is killed during
+        // a yield, by some concurrent event such as a collection drop.
         bool _failure;
 
         // If everything fails during the plan competition, we can't pick one.
         size_t _failureCount;
 
         // if pickBestPlan fails, this is set to the wsid of the statusMember
-        // returned by ::work() 
+        // returned by ::work()
         WorkingSetID _statusMemberId;
 
         // Stats