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: [EMAIL PROTECTED]
Telephone: +44 7786 702 706
MSN: [EMAIL PROTECTED]
Yahoo/AIM/Skype: maniksurtani
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