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From Michael Dürig <mdue...@apache.org>
Subject Re: [jr3 microkernel] Write skew
Date Thu, 01 Dec 2011 12:34:29 GMT


On 1.12.11 12:26, Felix Meschberger wrote:
>>> So we (thinking of Sling amongst other things) might have to adapt
>>> our event listeners to do a Session.refresh at the beginning of the
>>> onEvent method (in case long lived sessions are used).
>>
>> For obvious reasons a snapshot-based implementation would need to
>> implicitly call refresh(true) on a session before delivering
>> observation events.
>
> I don't think so, I would even deem it dangerous. Rather I would accept the fact of the
session not being accurate (since this is ok per the spec) and have the listeners refresh
themselves as needed.
>
> Maybe there are listeners, that do not even use the session, with which they have been
registered in the first place. Then such a refresh by the repository would just burn cycles
to no avail.

Another approach we discussed some time ago is to have read only 
sessions which are always on the newest revision (i.e. see all saved 
changes). Observation listeners on such sessions would then behave as 
they did with JR2. Since the underlying Microkernel implements an MVCC 
approach such read only sessions would be very easy and cheap to implement.

Michael

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