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From Jukka Zitting <jukka.zitt...@gmail.com>
Subject Re: [jr3 microkernel] Write skew
Date Thu, 01 Dec 2011 13:21:15 GMT

On Thu, Dec 1, 2011 at 1:21 PM, Michael Dürig <mduerig@apache.org> wrote:
> IIUC you want to "auto-refresh" all sessions each time observation events
> are being delivered?

Only those sessions to which events are being delivered, i.e. ones
that have explicitly registered an observation listener.

> Why do we 'obviously' need this? I understand, there will be a change from
> the current behaviour: while today sessions can't see items anymore which
> they get DELETE events for, in the new implementation sessions can't see
> items yet which they get ADD events for. From that perspective the new
> behaviour seems more flexible and complete: sessions can see deleted
> items until they do a refresh. Afterwards they can see the added items.

One of the few hard guarantees that we make to an observation listener
is that when an event is received, that change has already happened.
If the session state isn't refreshed when an even is delivered, then
the session would essentially be seeing into the future. I guess that
might be useful for some things like you mention, but to me that
sounds counterintuitive and as mentioned by Felix will likely trip off
many existing clients.


Jukka Zitting

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