Here is some more issue that I found afterwards:
I found that the time taken to fill arg2 is much more than it should, then I looked up the log file and found that the action to get arg2 has been invoked for 4 times, so the time taken for the UI to respond is 4x than it should be. This caused drastic performance degradation.
What has caused the action to be executed for more than once?
Thanks.