SERVER-16444 Copy data in the query subsystem as needed.

A WorkingSetMember in the LOC_AND_OBJ state must be made owned when:

  1. Its WorkingSetID is cached across multiple calls to work().

  2. Multiple calls to next(), seekExact(), saveState(), etc. are
     performed on the same WiredTiger cursor in a single work() call.

No longer necessary to always copy data out of WiredTiger buffers.

1 files changed, 11 insertions, 5 deletions

diff --git a/src/mongo/db/exec/delete.cpp b/src/mongo/db/exec/delete.cpp
index 1b970a475fc..b58354aa5d5 100644
--- a/src/mongo/db/exec/delete.cpp
+++ b/src/mongo/db/exec/delete.cpp
@@ -154,24 +154,27 @@ PlanStage::StageState DeleteStage::work(WorkingSetID* out) {
                 }
             }
 
+            // Ensure that the BSONObj underlying the WorkingSetMember is owned because saveState()
+            // is allowed to free the memory.
+            if (_params.returnDeleted) {
+                member->makeObjOwned();
+            }
+
             // TODO: Do we want to buffer docs and delete them in a group rather than
             // saving/restoring state repeatedly?
 
             try {
-                child()->saveState();
                 if (supportsDocLocking()) {
-                    // Doc-locking engines require this after saveState() since they don't use
+                    // Doc-locking engines require this before saveState() since they don't use
                     // invalidations.
                     WorkingSetCommon::prepareForSnapshotChange(_ws);
                 }
+                child()->saveState();
             } catch (const WriteConflictException& wce) {
                 std::terminate();
             }
 
             if (_params.returnDeleted) {
-                // Save a copy of the document that is about to get deleted.
-                BSONObj deletedDoc = member->obj.value();
-                member->obj.setValue(deletedDoc.getOwned());
                 member->loc = RecordId();
                 member->transitionToOwnedObj();
             }
@@ -185,6 +188,9 @@ PlanStage::StageState DeleteStage::work(WorkingSetID* out) {
 
             ++_specificStats.docsDeleted;
         } catch (const WriteConflictException& wce) {
+            // Ensure that the BSONObj underlying the WorkingSetMember is owned because it may be
+            // freed when we yield.
+            member->makeObjOwned();
             _idRetrying = id;
             memberFreer.Dismiss();  // Keep this member around so we can retry deleting it.
             *out = WorkingSet::INVALID_ID;