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From Felix Meschberger <fmesc...@adobe.com>
Subject Re: [jr3 microkernel] Write skew
Date Thu, 01 Dec 2011 10:59:46 GMT
Hi,

Am 30.11.2011 um 21:53 schrieb Jukka Zitting:

> Hi,
> 
> On Wed, Nov 30, 2011 at 3:21 PM, Michael Dürig <mduerig@apache.org> wrote:
>> 1) Does visible mean immediately visible on next access or visible after
>> refresh? The second case would work with snapshot isolation.
> 
> That's up the implementation.
> 
> Section 10.11.1 of JSR 283 [1] explicitly allows changes to become
> visible only after a refresh: "[...] items that do not have changes
> pending have their state refreshed to reflect the current persisted
> state, thus revealing changes made by other sessions."

Ok. Thanks for the clarification.

I always thought, what Jackrabbit currently does is required ... 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).

> 
> More generally about the write skew -issue; I don't think that's a
> common problem in practice. There aren't too many clients that
> explicitly interleave operations of multiple sessions within a single
> thread. And in a multithreaded setup a client would even with
> Jackrabbit 2.x need to use explicit synchronization to enforce more
> complex content constraints.

Sure. I think the main problem with long lived sessions I know of (in Sling based applications)
is with Observation Listeners which are quite isolated and can be "fixed" easily -- there
just has to be awareness.

Regards
Felix



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