<div dir="ltr"><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Mar 12, 2013 at 1:32 PM, Galder Zamarreño <span dir="ltr"><<a href="mailto:galder@redhat.com" target="_blank">galder@redhat.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im"><br>
On Mar 8, 2013, at 1:50 PM, Sanne Grinovero <<a href="mailto:sanne@infinispan.org">sanne@infinispan.org</a>> wrote:<br>
<br>
> Hi Galder,<br>
> I think using conditional operations is very useful even with<br>
> optimistic locking: the single conditional operation might not make<br>
> sense, but a transaction might include more operations and some of<br>
> these operations might depend on the result of the conditional<br>
> operation.<br>
><br>
> I'd expect the conditional operation to only return the value based on<br>
> current state (a prediction), and the transaction would fail if this<br>
> value is no longer valid at commit time. So no locks need to be taken<br>
> during the evaluation.<br>
<br>
</div>^ That's indeed what's happening, but as you can see, it confuses users (Jim, are you there?)…<br>
<br>
And I can see why they get confused. The conditional operations, such as replace, are rooted in enabling CAS-like operation, and an attempt to replace a value in a collection without having to synchronize or use locks…<br>
<br>
You can do what you say above with put/get operations. It will create more boiler plate code for sure, but the expectations of what the code does might be easier to understand for users.<br>
<br>
So, on one side, conditional operations can help reduce the code-size (by doing multiple operations in one go), but users expect them to behave in a way which does not really happen when you use transactions + OL.<br>
<br>
I'm in two minds on this…<br>
<br></blockquote><div><br></div><div>I remember having a discussion about conditional operations with optimistic locking a long time ago (Edinburgh?) and concluding that they should be allowed to "lie" - pretend that they did the put/replace/remove and check again on prepare if the condition still holds (with write skew check enabled).<br>
<br>I think the other option on the table was treat conditional operations as "non-transactional" - if putIfAbsent(k, v) returned true, then v would be stored in the cache even if the current transaction was rolled back.<br>
<br></div><div>I don't remember if we considered acquiring locks for conditional operations even with optimistic locking at the time or not. It would be a bit of a hack, but it would make a lot more sense than the current behaviour with the default configuration (optimistic locking with write skew check disabled, which makes conditional operations pretty much useless).<br>
</div><div><br></div><div>Off-topic: is it just me, or is it a little odd that the locking mode is configured via TransactionConfigurationBuilder and the isolation level/write skew check are configured via LockingConfigurationBuilder?<br>
<br></div><div>Cheers<br></div><div>Dan<br><br><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Cheers,<br>
<div class="HOEnZb"><div class="h5"><br>
><br>
> Sanne<br>
><br>
> On 6 March 2013 14:45, Galder Zamarreño <<a href="mailto:galder@redhat.com">galder@redhat.com</a>> wrote:<br>
>> Hi,<br>
>><br>
>> Re: <a href="https://issues.jboss.org/browse/ISPN-2891" target="_blank">https://issues.jboss.org/browse/ISPN-2891</a><br>
>><br>
>> Not sure what previous Infinispan version the AS instance Immutant guys used (5.1?), but seems like they're having more issues with the clojure test linked in the JIRA.<br>
>><br>
>> Again, we're talking about issues with replace(), but in a single node environment. They seem to have issues with PL and OL, but let's focus on OL for which there are logs attached.<br>
>><br>
>> Do conditional operations make any sense at all with OL? For example, can the return of replace() be taken a truthful in a transaction with OL?<br>
>><br>
>> As shown in the bad.log, this is not possible because lock acquisition and write skew checks are only done when the transaction is committed. So, what's the point of the conditional operations with OL? Their returns provide no guarantees whatsoever.<br>
>><br>
>> If this is known thing, I'm not aware of any docu on the topic.<br>
>><br>
>> Thoughts?<br>
>><br>
>> Cheers,<br>
>> --<br>
>> Galder Zamarreño<br>
>> <a href="mailto:galder@redhat.com">galder@redhat.com</a><br>
>> <a href="http://twitter.com/galderz" target="_blank">twitter.com/galderz</a><br>
>><br>
>> Project Lead, Escalante<br>
>> <a href="http://escalante.io" target="_blank">http://escalante.io</a><br>
>><br>
>> Engineer, Infinispan<br>
>> <a href="http://infinispan.org" target="_blank">http://infinispan.org</a><br>
>><br>
>><br>
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<br>
--<br>
Galder Zamarreño<br>
<a href="mailto:galder@redhat.com">galder@redhat.com</a><br>
<a href="http://twitter.com/galderz" target="_blank">twitter.com/galderz</a><br>
<br>
Project Lead, Escalante<br>
<a href="http://escalante.io" target="_blank">http://escalante.io</a><br>
<br>
Engineer, Infinispan<br>
<a href="http://infinispan.org" target="_blank">http://infinispan.org</a><br>
<br>
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