On 06/17/2013 12:56 PM, Mircea Markus wrote:
On 17 Jun 2013, at 11:52, Pedro Ruivo <pedro(a)infinispan.org> wrote:
> I've been looking at TxDistributionInterceptor and I have a couple of
> questions (assuming REPEATABLE_READ isolation level):
>
> #1. why are we doing a remote get each time we write on a key? (huge
> perform impact if the key was previously read)
indeed this is suboptimal for transactions that write the same key repeatedly and
repeatable read. Can you please create a JIRA for this?
created:
https://issues.jboss.org/browse/ISPN-3235
>
> #2. why are we doing a dataContainer.get() if the remote get returns a
> null value? Shouldn't the interactions with data container be performed
> only in the (Versioned)EntryWrappingInterceptor?
This was added in the scope of ISPN-2688 and covers the scenario in which a state
transfer is in progress, the remote get returns null as the remote value was dropped (no
longer owner) and this node has become the owner in between.
ok :)
>
> #3. (I didn't verify this) why are we acquire the lock is the remote get
> is performed for a write? This looks correct for pessimistic locking but
> not for optimistic...
I think that, given that the local node is not owner, the lock acquisition is redundant
even for pessimistic caches.
Mind creating a test to check if dropping that lock acquisition doesn't break things?
I created a JIRA with low priority since it does not affect the
transaction outcome/isolation and I believe the performance impact
should be lower (you can increase the priority if you want).
https://issues.jboss.org/browse/ISPN-3237
>
> After this analysis, it is possible to break the isolation between
> transaction if I do a get on the key that does not exist:
>
> tm.begin()
> cache.get(k) //returns null
> //in the meanwhile a transaction writes on k and commits
> cache.get(k) //return the new value. IMO, this is not valid for
> REPEATABLE_READ isolation level!
Indeed sounds like a bug, well spotted.
Can you please add a UT to confirm it and raise a JIRA?
created:
https://issues.jboss.org/browse/ISPN-3236
IMO, this should be the correct behaviour (I'm going to add the test
cases later):
tm.begin()
cache.get(k) //returns null (op#1)
//in the meanwhile a transaction writes on k and commits
write operation performed:
* put: must return the same value as op#1
* conditional put //if op#1 returns null the operation should be always
successful (i.e. the key is updated, return true). Otherwise, the key
remains unchanged (return false)
* replace: must return the same value as op#1
* conditional replace: replace should be successful if checked with the
op#1 return value (return true). Otherwise, the key must remain
unchanged (return false).
* remote: must return the same value as op#1
* conditional remove: the key should be removed if checked with the op#1
return value (return true). Otherwise, the key must remain unchanged
(return false)
Also, the description above should be valid after a removal of a key.
Cheers,