SERVER-12952 do less work for non-matching index docs

2 files changed, 73 insertions, 11 deletions

diff --git a/src/mongo/db/exec/filter.h b/src/mongo/db/exec/filter.h
index ff9916bfb27..8fdd3b8be80 100644
--- a/src/mongo/db/exec/filter.h
+++ b/src/mongo/db/exec/filter.h
@@ -46,7 +46,7 @@ namespace mongo {
         // This is only called by a $where query.  The query system must be smart enough to realize
         // that it should do a fetch beforehand.
         BSONObj toBSON() const {
-            verify(_wsm->hasObj());
+            invariant(_wsm->hasObj());
             return _wsm->obj;
         }
 
@@ -67,7 +67,7 @@ namespace mongo {
 
                 while (keyPatternIt.more()) {
                     BSONElement keyPatternElt = keyPatternIt.next();
-                    verify(keyDataIt.more());
+                    invariant(keyDataIt.more());
                     BSONElement keyDataElt = keyDataIt.next();
 
                     if (path->fieldRef().equalsDottedField(keyPatternElt.fieldName())) {
@@ -96,6 +96,53 @@ namespace mongo {
         WorkingSetMember* _wsm;
     };
 
+    class IndexKeyMatchableDocument : public MatchableDocument {
+    public:
+        IndexKeyMatchableDocument(const BSONObj& key,
+                                  const BSONObj& keyPattern)
+            : _keyPattern(keyPattern), _key(key) { }
+
+        BSONObj toBSON() const {
+            // Planning shouldn't let this happen.
+            invariant(0);
+        }
+
+        virtual ElementIterator* allocateIterator(const ElementPath* path) const {
+            BSONObjIterator keyPatternIt(_keyPattern);
+            BSONObjIterator keyDataIt(_key);
+
+            while (keyPatternIt.more()) {
+                BSONElement keyPatternElt = keyPatternIt.next();
+                invariant(keyDataIt.more());
+                BSONElement keyDataElt = keyDataIt.next();
+
+                if (path->fieldRef().equalsDottedField(keyPatternElt.fieldName())) {
+                    if (Array == keyDataElt.type()) {
+                        return new SimpleArrayElementIterator(keyDataElt, true);
+                    }
+                    else {
+                        return new SingleElementElementIterator(keyDataElt);
+                    }
+                }
+            }
+
+            // Planning should not let this happen.
+            massert(17409,
+                    "trying to match on unknown field: " + path->fieldRef().dottedField().toString(),
+                    0);
+
+            return new SingleElementElementIterator(BSONElement());
+        }
+
+        virtual void releaseIterator(ElementIterator* iterator) const {
+            delete iterator;
+        }
+
+    private:
+        BSONObj _keyPattern;
+        BSONObj _key;
+    };
+
     /**
      * Used by every stage with a filter.
      */
@@ -110,6 +157,15 @@ namespace mongo {
             WorkingSetMatchableDocument doc(wsm);
             return filter->matches(&doc, NULL);
         }
+
+        static bool passes(const BSONObj& keyData,
+                           const BSONObj& keyPattern,
+                           const MatchExpression* filter) {
+
+            if (NULL == filter) { return true; }
+            IndexKeyMatchableDocument doc(keyData, keyPattern);
+            return filter->matches(&doc, NULL);
+        }
     };
 
 }  // namespace mongo
diff --git a/src/mongo/db/exec/index_scan.cpp b/src/mongo/db/exec/index_scan.cpp
index 0c7b1dd937a..31c8b58b4c1 100644
--- a/src/mongo/db/exec/index_scan.cpp
+++ b/src/mongo/db/exec/index_scan.cpp
@@ -140,7 +140,7 @@ namespace mongo {
         if (isEOF()) { return PlanStage::IS_EOF; }
 
         // Grab the next (key, value) from the index.
-        BSONObj ownedKeyObj = _indexCursor->getKey().getOwned();
+        BSONObj keyObj = _indexCursor->getKey();
         DiskLoc loc = _indexCursor->getValue();
 
         // Move to the next result.
@@ -162,27 +162,33 @@ namespace mongo {
             }
         }
 
-        WorkingSetID id = _workingSet->allocate();
-        WorkingSetMember* member = _workingSet->get(id);
-        member->loc = loc;
-        member->keyData.push_back(IndexKeyDatum(_descriptor->keyPattern(), ownedKeyObj));
-        member->state = WorkingSetMember::LOC_AND_IDX;
-
-        if (Filter::passes(member, _filter)) {
+        if (Filter::passes(keyObj, _descriptor->keyPattern(), _filter)) {
             if (NULL != _filter) {
                 ++_specificStats.matchTested;
             }
+
+            // We must make a copy of the on-disk data since it can mutate during the execution of
+            // this query.
+            BSONObj ownedKeyObj = keyObj.getOwned();
+
+            // Fill out the WSM.
+            WorkingSetID id = _workingSet->allocate();
+            WorkingSetMember* member = _workingSet->get(id);
+            member->loc = loc;
+            member->keyData.push_back(IndexKeyDatum(_descriptor->keyPattern(), ownedKeyObj));
+            member->state = WorkingSetMember::LOC_AND_IDX;
+
             if (_params.addKeyMetadata) {
                 BSONObjBuilder bob;
                 bob.appendKeys(_descriptor->keyPattern(), ownedKeyObj);
                 member->addComputed(new IndexKeyComputedData(bob.obj()));
             }
+
             *out = id;
             ++_commonStats.advanced;
             return PlanStage::ADVANCED;
         }
 
-        _workingSet->free(id);
         ++_commonStats.needTime;
         return PlanStage::NEED_TIME;
     }