When running regression test, we always found that the query return empty result after loading finished,
even if we call "sync" before the query.
This is because for `stream load`, the load task result will be returned immediately after the txn's status changed to VISIBLE,
but before writing the edit log.
So if we do the query right after we got the load task result, it is possible that we can not see the latest loaded data.
Same issue with `insert` operation