Manager muc history problems

Dear all,

I am a new developer to xmpp. Hope to get some feedback from you guys.

I am working on a application using xmpp muc, and I use openfire as backend. For the chatting room, I hope everyone in the  room  can view the whole history since the room created, but I  don't want to load whole history while user enters the room.

The request is, user can use a button like "load more history" to fetch the earlier history.

I know I can send

<presence

    from='hag66@shakespeare.lit/pda'

    id='n13mt3l'

    to='coven@chat.shakespeare.lit/thirdwitch'>

  <x xmlns='http://jabber.org/protocol/muc'>

    <history seconds='180'/>

  </x>

</presence>

to manage history, but what should I do? leave the room and re-join the room again to get earlier history?

Following settings I have enable on openfire server:

- Log room conversations

- Every room is persistent

Any advice is welcome.

Thanks.

Johnny