Remove duplicate code (#8079)

Summary:
The implementation of TransactionDB::WrapDB() and
TransactionDB::WrapStackableDB() are almost identical, except for the
type of the first argument `db`. This PR adds a new template function in
anonymous namespace, and calls it in the above two functions.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8079

Test Plan: make check

Reviewed By: lth

Differential Revision: D27184575

Pulled By: riversand963

fbshipit-source-id: f2855a6db3a7e897d0d611f7050ca4b696c56a7a

utilities/transactions/pessimistic_transaction_db.cc

@@ -276,10 +276,10 @@ void TransactionDB::PrepareWrap(
   db_options->allow_2pc = true;
 }
 
-Status TransactionDB::WrapDB(
-    // make sure this db is already opened with memtable history enabled,
-    // auto compaction distabled and 2 phase commit enabled
-    DB* db, const TransactionDBOptions& txn_db_options,
+namespace {
+template <typename DBType>
+Status WrapAnotherDBInternal(
+    DBType* db, const TransactionDBOptions& txn_db_options,
     const std::vector<size_t>& compaction_enabled_cf_indices,
     const std::vector<ColumnFamilyHandle*>& handles, TransactionDB** dbptr) {
   assert(db != nullptr);
@@ -309,6 +309,17 @@ Status TransactionDB::WrapDB(
   }
   return s;
 }
+}  // namespace
+
+Status TransactionDB::WrapDB(
+    // make sure this db is already opened with memtable history enabled,
+    // auto compaction distabled and 2 phase commit enabled
+    DB* db, const TransactionDBOptions& txn_db_options,
+    const std::vector<size_t>& compaction_enabled_cf_indices,
+    const std::vector<ColumnFamilyHandle*>& handles, TransactionDB** dbptr) {
+  return WrapAnotherDBInternal(db, txn_db_options,
+                               compaction_enabled_cf_indices, handles, dbptr);
+}
 
 Status TransactionDB::WrapStackableDB(
     // make sure this stackable_db is already opened with memtable history
@@ -316,33 +327,8 @@ Status TransactionDB::WrapStackableDB(
     StackableDB* db, const TransactionDBOptions& txn_db_options,
     const std::vector<size_t>& compaction_enabled_cf_indices,
     const std::vector<ColumnFamilyHandle*>& handles, TransactionDB** dbptr) {
-  assert(db != nullptr);
-  assert(dbptr != nullptr);
-  *dbptr = nullptr;
-  std::unique_ptr<PessimisticTransactionDB> txn_db;
-
-  switch (txn_db_options.write_policy) {
-    case WRITE_UNPREPARED:
-      txn_db.reset(new WriteUnpreparedTxnDB(
-          db, PessimisticTransactionDB::ValidateTxnDBOptions(txn_db_options)));
-      break;
-    case WRITE_PREPARED:
-      txn_db.reset(new WritePreparedTxnDB(
-          db, PessimisticTransactionDB::ValidateTxnDBOptions(txn_db_options)));
-      break;
-    case WRITE_COMMITTED:
-    default:
-      txn_db.reset(new WriteCommittedTxnDB(
-          db, PessimisticTransactionDB::ValidateTxnDBOptions(txn_db_options)));
-  }
-  txn_db->UpdateCFComparatorMap(handles);
-  Status s = txn_db->Initialize(compaction_enabled_cf_indices, handles);
-  // In case of a failure at this point, db is deleted via the txn_db destructor
-  // and set to nullptr.
-  if (s.ok()) {
-    *dbptr = txn_db.release();
-  }
-  return s;
+  return WrapAnotherDBInternal(db, txn_db_options,
+                               compaction_enabled_cf_indices, handles, dbptr);
 }
 
 // Let LockManager know that this column family exists so it can