[infinispan-dev] Fix or document? Concurrent replaceWithVersion w/ same value might all return true - ISPN-4972

[Tristan Tarrant]

It depends on the side-effects that replacing something with the same 
value has: listeners, cachestores, state transfer, etc.
In general I'd say: no that's not what I want.

Tristan

On 26/11/14 16:43, Sanne Grinovero wrote:
> On 26 November 2014 at 14:17, Dan Berindei <dan.berindei at gmail.com> wrote:
>> Sanne, it will work as long as the previous value is not the same as
>> the new value.
>>
>> If multiple threads read value 5 with version 5, and all of them want
>> to replace it with value 6, only one of them will succeed.
> Ok I see I might be confusing value and versions. I hope :)
>
>> But if multiple threads read value 5 with version 5, and want to
>> replace it with value *5*, all of them might succeed.
> This paragraph is confusing me more. What "value" are you referring to
> at the third "5"? Is it even legal to replace an entry with a new
> value but not incrementing its version?
>
> Thanks!
> Sanne
>
>> Indeed, it's not atomic, but a basic counter will work. And it's all
>> we can do with the actual core cache API (unless we want to go back to
>> including the HotRod version in the value).
>>
>> Cheers
>> Dan
>>
>>
>> On Wed, Nov 26, 2014 at 2:33 PM, Sanne Grinovero <sanne at infinispan.org> wrote:
>>> That's not Atomic. How can I implement a counter on this?
>>>
>>> Say the current version is 5, I read it, and then issue a "replace 5
>>> with 6" command.
>>> If I send a couple of such commands in parallel I need a guarantee
>>> that only one succeeds, so that the other one can retry and get the
>>> counter up to 7.
>>>
>>> Over Hot Rod I have no locking so I have no alternatives other than
>>> atomic replacement commands, that's not unlikely to happen: that's a
>>> critical showstopper for users.
>>>
>>> Sanne
>>>
>>>
>>> On 20 November 2014 at 16:35, Dan Berindei <dan.berindei at gmail.com> wrote:
>>>> I guess you could say this is a regression, this wouldn't have been possible
>>>> when the version was part of the value :)
>>>>
>>>> But I agree an application is very unlikely call replaceWithVersion with the
>>>> same value as before, so +1 to document it for now and implement
>>>> replaceWithVersion/replaceWithPredicate in the embedded cache for 8.0.
>>>>
>>>> Cheers
>>>> Dan
>>>>
>>>>
>>>> On Thu, Nov 13, 2014 at 3:08 PM, Radim Vansa <rvansa at redhat.com> wrote:
>>>>> I agree with Galder, fixing it is not worth the cost.
>>>>>
>>>>> Actually, there are often bugs that I'd call rather 'quirks', not
>>>>> honoring the ConcurrentMap contract (recently we have discussed with Dan
>>>>> [1] and [2]) which are quite complex to fix. Another one that's
>>>>> considered not a bug is that a read does not have transactional semantics.
>>>>> Galder, where will you document that? I think that special page in
>>>>> documentation should accumulate such cases, linked to JIRAs for case
>>>>> that eventually we'll resolve them (with that glorious MVCC). And of
>>>>> course, link from javadoc to this document (though I am not sure whether
>>>>> we can correctly keep that in sync with latest release. Could we have a
>>>>> redirection from http://infinispan.org/docs/latest to
>>>>> http://infinispan.org/docs/7.0.x/ ?
>>>>>
>>>>> Radim
>>>>>
>>>>> [1] https://issues.jboss.org/browse/ISPN-3918
>>>>> [2] https://issues.jboss.org/browse/ISPN-4286
>>>>>
>>>>> On 11/13/2014 01:51 PM, Galder Zamarreño wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> Re: https://issues.jboss.org/browse/ISPN-4972
>>>>>>
>>>>>> Embedded cache provides atomicity of a replace() call passing in the
>>>>>> previous value. This limitation might be lifted when we adopt Java 8 and we
>>>>>> can pass in a lambda or similar, which can be executed right when the value
>>>>>> is compared now, and if it returns true it’s applied. The lambda could
>>>>>> compare both value and metadata for example.
>>>>>>
>>>>>> Anyway, given the current status, I’m considering whether it’s worth
>>>>>> fixing this particular issue. Fixing the issue would require adding some
>>>>>> kind of locking in the Hot Rod server so that the version retrieval,
>>>>>> comparison and replace call, can all happen atomically.
>>>>>>
>>>>>> This is not ideal, and on top of that, as Radim said, the chances of
>>>>>> this happening in real life are limited, or more precisely it’s effects are
>>>>>> minimal. In other words, if two concurrent threads call replace with the
>>>>>> same value, the end result is that the new value would be stored, but as a
>>>>>> result of the code, both replaces would return true which is not strictly
>>>>>> right.
>>>>>>
>>>>>> I’d rather document this than add unnecessary locking in the Hot Rod
>>>>>> server where it deals with the versioned replace call.
>>>>>>
>>>>>> Thoughts?
>>>>>> --
>>>>>> Galder Zamarreño
>>>>>> galder at redhat.com
>>>>>> twitter.com/galderz
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> infinispan-dev mailing list
>>>>>> infinispan-dev at lists.jboss.org
>>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>
>>>>> --
>>>>> Radim Vansa <rvansa at redhat.com>
>>>>> JBoss DataGrid QA
>>>>>
>>>>> _______________________________________________
>>>>> infinispan-dev mailing list
>>>>> infinispan-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>
>>>>
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-- 
--
Tristan Tarrant
Infinispan Lead
JBoss, a division of Red Hat