update benchmark

benchmarks/db_bench.cc

@@ -1127,8 +1127,8 @@ int main(int argc, char** argv) {
 
   // Choose a location for the test database if none given with --db=<path>
   if (FLAGS_db == nullptr) {
-    leveldb::g_env->GetTestDirectory(&default_db_path);
-    default_db_path += "/dbbench";
+    //leveldb::g_env->GetTestDirectory(&default_db_path);
+    default_db_path = "dbbench";
     FLAGS_db = default_db_path.c_str();
   }