V3.2 - Reinserting oplog hack for last record retrieval (#91)

* Reinserting oplog hack for first record retrieval. * Removed extra space. * Added oplog hack for backward cursors as well.
mongodb-partners · Aug 1, 2017 · 422336c · 422336c
1 parent 038daba
commit 422336c
Showing 1 changed file with 17 additions and 11 deletions.
diff --git a/src/rocks_record_store.cpp b/src/rocks_record_store.cpp
@@ -763,19 +763,25 @@ namespace mongo {
 
     std::unique_ptr<SeekableRecordCursor> RocksRecordStore::getCursor(OperationContext* txn,
                                                                       bool forward) const {
-        if (_isOplog && forward) {
-            auto ru = RocksRecoveryUnit::getRocksRecoveryUnit(txn);
-            // If we already have a snapshot we don't know what it can see, unless we know no
-            // one else could be writing (because we hold an exclusive lock).
-            if (ru->hasSnapshot() && !txn->lockState()->isNoop() &&
-                !txn->lockState()->isCollectionLockedForMode(_ns, MODE_X)) {
-                throw WriteConflictException();
+        RecordId startIterator;
+        if (_isOplog) {
+            if (forward) {
+                auto ru = RocksRecoveryUnit::getRocksRecoveryUnit(txn);
+                // If we already have a snapshot we don't know what it can see, unless we know no
+                // one else could be writing (because we hold an exclusive lock).
+                if (ru->hasSnapshot() && !txn->lockState()->isNoop() &&
+                    !txn->lockState()->isCollectionLockedForMode(_ns, MODE_X)) {
+                    throw WriteConflictException();
+                }
+                ru->setOplogReadTill(_cappedVisibilityManager->oplogStartHack());
+                startIterator = _cappedOldestKeyHint;
+            } else {
+                startIterator = _cappedVisibilityManager->oplogStartHack();
             }
-            ru->setOplogReadTill(_cappedVisibilityManager->oplogStartHack());
         }
 
         return stdx::make_unique<Cursor>(txn, _db, _prefix, _cappedVisibilityManager, forward,
-                                         _isCapped, _cappedOldestKeyHint);
+                                         _isCapped, startIterator);
     }
 
     Status RocksRecordStore::truncate(OperationContext* txn) {
@@ -1060,8 +1066,8 @@ namespace mongo {
         _currentSequenceNumber =
           RocksRecoveryUnit::getRocksRecoveryUnit(txn)->snapshot()->GetSequenceNumber();
 
-        if (!startIterator.isNull() && !_readUntilForOplog.isNull() && forward) {
-            // This is a hack to speed up first record retrieval from the oplog
+        if (!startIterator.isNull()) {
+            // This is a hack to speed up first/last record retrieval from the oplog
             _needFirstSeek = false;
             _lastLoc = startIterator;
             iterator();