On Sep 24, 2012, at 12:27 PM, Manik Surtani <manik(a)jboss.org> wrote:
>
> On 24 Sep 2012, at 11:01, Galder Zamarreño <galder(a)redhat.com> wrote:
>
>>
>> On Sep 21, 2012, at 3:43 PM, Sanne Grinovero <sanne(a)infinispan.org> wrote:
>>
>>> On 20 September 2012 17:38, Andrig Miller <anmiller(a)redhat.com> wrote:
>>>>
>>>>
>>>> ----- Original Message -----
>>>>> From: "Galder Zamarreño" <galder(a)redhat.com>
>>>>> To: "Andrig Miller" <anmiller(a)redhat.com>
>>>>> Cc: "Steve Ebersole" <steve(a)hibernate.org>,
"John O'Hara" <johara(a)redhat.com>, "Jeremy Whiting"
>>>>> <jwhiting(a)redhat.com>, "infinispan -Dev List"
<infinispan-dev(a)lists.jboss.org>
>>>>> Sent: Thursday, September 20, 2012 6:48:59 AM
>>>>> Subject: Re: [infinispan-dev] Issue with cache blocks for local
read-only cache
>>>>>
>>>>>
>>>>> On Sep 19, 2012, at 4:20 PM, Andrig Miller
<anmiller(a)redhat.com>
>>>>> wrote:
>>>>>
>>>>>> Yes, I can see how that can happen, if the data is deleted from
>>>>>> outside the application.
>>>>>
>>>>> ^ The issue does not only happen if the data is deleted outside the
>>>>> application. As indicated in
>>>>>
https://hibernate.onjira.com/browse/HHH-3817, this can happen with
>>>>> two competing transactions.
>>>>>
>>>>>> If you cache something as READ_ONLY, and it gets deleted, that
>>>>>> doesn't fit the definition of READ_ONLY though. You are
using the
>>>>>> wrong cache concurrency strategy.
>>>>>>
>>>>>> Even that issue outlines the scenario where the collection is
>>>>>> updated, which means its not a READ_ONLY.
>>>>>
>>>>> I think the update is irrelevant here. The issue is related to
>>>>> putFromLoad + remove, which both AFAIK, are allowed in READ_ONLY
>>>>> (remember that we had the discussion on whether remove should be
>>>>> allowed in a READ_ONLY cache:
>>>>>
https://hibernate.onjira.com/browse/HHH-7350).
>>>>>
>>>>
>>>> Yes, remove can be done, its just update that matters to READ_ONLY. One
thing I thought about was I thought we were using MVCC for this stuff. Any transaction
that reads from the cache, while something is being added/removed, should be reading the
read consistent image, and should never wait on a lock, correct? We see all the threads
in our thread pool sitting in a blocked state based on this locking.
>>
>> I'm not 100% sure which locking are you talking about, but if you're
refering to the lock in
https://dl.dropbox.com/u/30971563/specjent_block.png, that's
related to the 2LC integration, not Infinispan itself.
>
> Yes, we're analysing the 2LC impl as well as Infinispan.
>
>> If you're talking about threads waiting for a lock somewhere else, please
provide more details.
>>
>> I have some short-term ideas to improve the 2LC integration code, but I wanna
check with Brian first.
>>
>> Long term, I think
https://issues.jboss.org/browse/ISPN-506 will be necessary to
provide a lock-free solution to these edge cases in such way that 'newer' removes
cannot be overridden by 'old' putFromLoad calls. However, I'm intrigued by the
fact that JBoss Cache OL had the capability of being given a version externally, but the
2LC code for JBoss Cache OL still used this PutFromLoadValidator logic. Again, something I
need to check with Brian.
>
> ISPN-506 will only help in the clustered case.
^ I disagree. It might help with the edge case highlighted in
https://hibernate.onjira.com/browse/HHH-3817 which happens in a local cache.
There is a much easier way to solve this: pessimistic locking + an eager cache.lock()
command before retrieving the collection from the database. This will prevent the race
defined in the HHH-3817.
--
Manik Surtani
manik(a)jboss.org