Implement NextAndGetResult() in memtable and level iterator (#7179)

Summary:
NextAndGetResult() is not implemented in memtable and is very simply implemented in level iterator. The result is that for a normal leveled iterator, performance regression will be observed for calling PrepareValue() for most iterator Next(). Mitigate the problem by implementing the function for both iterators. In level iterator, the implementation cannot be perfect as when calling file iterator's SeekToFirst() we don't have information about whether the value is prepared. Fortunately, the first key should not cause a big portion of the CPu.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7179

Test Plan: Run normal crash test for a while.

Reviewed By: anand1976

Differential Revision: D22783840

fbshipit-source-id: c19f45cdf21b756190adef97a3b66ccde3936e05

1 files changed, 7 insertions, 0 deletions

diff --git a/table/iterator_wrapper.h b/table/iterator_wrapper.h
index b4b051ff6..010a23abf 100644
--- a/table/iterator_wrapper.h
+++ b/table/iterator_wrapper.h
@@ -89,6 +89,13 @@ class IteratorWrapperBase {
     valid_ = iter_->NextAndGetResult(&result_);
     assert(!valid_ || iter_->status().ok());
   }
+  bool NextAndGetResult(IterateResult* result) {
+    assert(iter_);
+    valid_ = iter_->NextAndGetResult(&result_);
+    *result = result_;
+    assert(!valid_ || iter_->status().ok());
+    return valid_;
+  }
   void Prev() {
     assert(iter_);
     iter_->Prev();