[hibernate-dev] Re: [jbosscache-dev] Re: JBoss Cache and Hibernate Integration

[Manik Surtani]

On 31 Mar 2007, at 19:01, Owen Taylor wrote:

> On Fri, 2007-03-16 at 01:23 +0000, Manik Surtani wrote:
>> Guys,
>>
>> I've updated the JIRA [1] and the Javadocs on the Cache interface [2]
>> to reflect the new functioning of putForExternalRead(), which I will
>> implement by 2.0.0.BETA2.
>
> This looks like a reasonable specification to me.
>
>> Just like to clarify that there was also some thought around using
>> READ locks for the call when pessimistic locking is used.  There was
>> also talk about potentially forcing READ_COMMITTED as an isolation
>> level for this call if the isolation level used is anything
>> stronger.  Probably points I should have brought up on the call, but
>> are there any thoughts around these?
>>
>> I'm happy with using a RL instead of a WL simply because we intend to
>> only carry out this operation if the node does not exist (see first
>> bullet point in the javadoc).  Because of this though, I don't see
>> how forcing READ_COMMITTED can benefit much, and would just add
>> complexity unnecessarily.
>
> Because the current transaction is suspended, REPEATABLE_READ vs.
> READ_COMMITTED seems pretty much irrelevant ... we aren't going
> to hold any locks after the operation finishes.
>
> That, and the fact that the node doesn't already exists,
> also means that the difference between write locks and read
> locks is pretty small ... the only difference is what happens when
> someone else reads between:
>
>  - The update to the node finishes
>  - We release our locks
>
> Right? As long as data-structure integrity is preserved, using
> a read lock should be OK, but I think the distinction isn't
> going to matter much.
>
> (This is, of course, because JBossCache doesn't acquire locks
> across the cluster on a write, but just lets the transaction roll
> back on commit in case of conflict.
>
> If JBossCache did acquire cluster locks on a write, then a write
> lock would be much more expensive and avoiding it a big win.)
>
> 					 - Owen
>

This is pretty much what I thought.  Not included these in the  
putForExternalRead() spec as a result.

Cheers,
--
Manik Surtani

Lead, JBoss Cache
JBoss, a division of Red Hat

Email: manik at jboss.org
Telephone: +44 7786 702 706
MSN: manik at surtani.org
Yahoo/AIM/Skype: maniksurtani