refine code (#6420)

Summary:
I create a new branch from the branch new upsteram/master and "git merge --squash".
Maybe it will fix everything.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6420

Differential Revision: D19897152

Pulled By: zhichao-cao

fbshipit-source-id: 6575d9e3b23e360f42ee1480b43028b5fcc20136

utilities/transactions/optimistic_transaction.cc

@@ -59,13 +59,13 @@ Status OptimisticTransaction::Commit() {
   auto txn_db_impl = static_cast_with_check<OptimisticTransactionDBImpl,
                                             OptimisticTransactionDB>(txn_db_);
   assert(txn_db_impl);
-  OccValidationPolicy policy = txn_db_impl->GetValidatePolicy();
+  switch (txn_db_impl->GetValidatePolicy()) {
-  if (policy == OccValidationPolicy::kValidateParallel) {
+    case OccValidationPolicy::kValidateParallel:
-    return CommitWithParallelValidate();
+      return CommitWithParallelValidate();
-  } else if (policy == OccValidationPolicy::kValidateSerial) {
+    case OccValidationPolicy::kValidateSerial:
-    return CommitWithSerialValidate();
+      return CommitWithSerialValidate();
-  } else {
+    default:
-    assert(0);
+      assert(0);
   }
   // unreachable, just void compiler complain
   return Status::OK();