<p dir="ltr">+1<br>
You had me convinced at the first line, although "A lot of code can now be removed and made simpler" makes it look extremely nice. <br>
</p>
<div class="gmail_quote">On 13 Jul 2015 18:14, "William Burns" <<a href="mailto:mudokonman@gmail.com">mudokonman@gmail.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">This is a necro of [1].<div><br></div><div>With Infinispan 8.0 we are adding in clustered expiration. That includes an expiration event raised that is clustered as well. Unfortunately expiration events currently occur multiple times (if numOwners > 1) at different times across nodes in a cluster. This makes coordinating a single cluster expiration event quite difficult.</div><div><br></div><div>To work around this I am proposing that the expiration of an event is done solely by the owner of the given key that is now expired. This would fix the issue of having multiple events and the event can be raised while holding the lock for the given key so concurrent modifications would not be an issue.</div><div><br></div><div>The problem arises when you have other nodes that have expiration set but expire at different times. Max idle is the biggest offender with this as a read on an owner only refreshes the owners timestamp, meaning other owners would not be updated and expire preemptively. To have expiration work properly in this case you would need coordination between the owners to see if anyone has a higher value. This requires blocking and would have to be done while accessing a key that is expired to be sure if expiration happened or not.</div><div><br></div><div>The linked dev listing proposed instead to only expire an entry by the reaper thread and not on access. In this case a read will return a non null value until it is fully expired, increasing hit ratios possibly.</div><div><br></div><div>Their are quire a bit of real benefits for this:</div><div><br></div><div>1. Cluster cache reads would be much simpler and wouldn't have to block to verify the object exists or not since this would only be done by the reaper thread (note this would have only happened if the entry was expired locally). An access would just return the value immediately.</div><div>2. Each node only expires entries it owns in the reaper thread reducing how many entries they must check or remove. This also provides a single point where events would be raised as we need.</div><div>3. A lot of code can now be removed and made simpler as it no longer has to check for expiration. The expiration check would only be done in 1 place, the expiration reaper thread.</div><div><br></div><div>The main issue with this proposal is as the other listing mentions is if user code expects the value to be gone after expiration for correctness. I would say this use case is not as compelling for maxIdle, especially since we never supported it properly. And in the case of lifespan the user could very easily store the expiration time in the object that they can check after a get as pointed out in the other thread.</div><div><br></div><div>[1] <a href="http://infinispan-developer-list.980875.n3.nabble.com/infinispan-dev-strictly-not-returning-expired-values-td3428763.html" target="_blank">http://infinispan-developer-list.980875.n3.nabble.com/infinispan-dev-strictly-not-returning-expired-values-td3428763.html</a></div></div>
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