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. And SpecJ - and most other use cases - are
not clustered. Maybe we need two 2LC implementations, one for clustered and one for
non-clustered use? There are a lot of unnecessary locks that can be removed in the local
case. Sanne and I were having a chat about this yesterday.
- M
--
Manik Surtani
manik(a)jboss.org
twitter.com/maniksurtani
Platform Architect, JBoss Data Grid
http://red.ht/data-grid