Re: [infinispan-dev] To Optional or not to Optional?

I wouldn't say I'm an extreme naysayer, but I do have 2 issues with Optional: 1. Performance becomes harder to quantify: the allocations may or may not be eliminated, and a change in one part of the code may change how allocations are eliminated in a completely different part of the code. 2. My personal opinion is it's just ugly... instead of having one field that could be null or non-null, you now have a field that could be null, Optional.empty(), or Optional.of(something). Cheers Dan On Tue, May 23, 2017 at 1:54 PM, Sebastian Laskawiec <slaskawi(a)redhat.com&gt; wrote: > Hey! > > So I think we have no extreme naysayers to Optional. So let me try to sum > up what we have achieved so: > > - In macroscale benchmark based on REST interface using Optionals > didn't lower the performance. > - +1 for using it in public APIs, especially for those using > functional style. > - Creating lots of Optional instances might add some pressure on GC, > so we need to be careful when using them in hot code paths. In such cases > it is required to run a micro scale benchamark to make sure the performance > didn't drop. The microbenchmark should also be followed by macro scale > benchamrk - PerfJobAck. Also, keep an eye on Eden space in such cases. > > If you agree with me, and there are no hard evidence that using Optional > degrade performance significantly, I would like to issue a pull request and > put those findings into contributing guide [1]. > > Thanks, > Sebastian > > [1] https://github.com/infinispan/infinispan/tree/master/ > documentation/src/main/asciidoc/contributing > > On Mon, May 22, 2017 at 6:36 PM Galder Zamarreño <galder(a)redhat.com&gt; > wrote: > >> I think Sanne's right here, any differences in such large scale test are >> hard to decipher. >> >> Also, as mentioned in a previous email, my view on its usage is same as >> Sanne's: >> >> * Definitely in APIs/SPIs. >> * Be gentle with it internals. >> >> Cheers, >> -- >> Galder Zamarreño >> Infinispan, Red Hat >> >> > On 18 May 2017, at 14:35, Sanne Grinovero <sanne(a)infinispan.org&gt; >> wrote: >> > >> > Hi Sebastian, >> > >> > sorry but I think you've been wasting time, I hope it was fun :) This >> is not the right methodology to "settle" the matter (unless you want >> Radim's eyes to get bloody..). >> > >> > Any change in such a complex system will only affect the performance >> metrics if you're actually addressing the dominant bottleneck. In some >> cases it might be CPU, like if your system is at 90%+ CPU then it's likely >> that reviewing the code to use less CPU would be beneficial; but even that >> can be counter-productive, for example if you're having contention caused >> by optimistic locking and you fail to address that while making something >> else "faster" the performance loss on the optimistic lock might become >> asymptotic. >> > >> > A good reason to avoid excessive usage of Optional (and *excessive* >> doesn't mean a couple dozen in a millions lines of code..) is to not run >> out of eden space, especially for all the code running in interpreted mode. >> > >> > In your case you've been benchmarking a hugely complex beast, not >> least over REST! When running the REST Server I doubt that allocation in >> eden is your main problem. You just happened to have a couple Optionals on >> your path; sure performance changed but there's no enough data in this way >> to figure out what exactly happened: >> > - did it change at all or was it just because of a lucky >> optimisation? (The JIT will always optimise stuff differently even when >> re-running the same code) >> > - did the overall picture improve because this code became much >> *less* slower? >> > >> > The real complexity in benchmarking is to accurately understand why it >> changed; this should also tell you why it didn't change more, or less.. >> > >> > To be fair I actually agree that it's very likely that C2 can make any >> performance penalty disappear.. that's totally possible, although it's >> unlikely to be faster than just reading the field (assuming we don't need >> to do branching because of null-checks but C2 can optimise that as well). >> > Still this requires the code to be optimised by JIT first, so it won't >> prevent us from creating a gazillion of instances if we abuse its usage >> irresponsibly. Fighting internal NPEs is a matter of writing better code; >> I'm not against some "Optional" being strategically placed but I believe >> it's much nicer for most internal code to just avoid null, use "final", and >> initialize things aggressively. >> > >> > Sure use Optional where it makes sense, probably most on APIs and >> SPIs, but please don't go overboard with it in internals. That's all I said >> in the original debate. >> > >> > In case you want to benchmark the impact of Optional make a JMH based >> microbenchmark - that's interesting to see what C2 is capable of - but even >> so that's not going to tell you much on the impact it would have to patch >> thousands of code all around Infinispan. And it will need some peer review >> before it can tell you anything at all ;) >> > >> > It's actually a very challenging topic, as we produce libraries meant >> for "anyone to use" and don't get to set the hardware specification >> requirements it's hard to predict if we should optimise the system for >> this/that resource consumption. Some people will have plenty of CPU and >> have problems with us needing too much memory, some others will have the >> opposite.. the real challenge is in making internals "elastic" to such >> factors and adaptable without making it too hard to tune. >> > >> > Thanks, >> > Sanne >> > >> > >> > >> > On 18 May 2017 at 12:30, Sebastian Laskawiec <slaskawi(a)redhat.com&gt; >> wrote: >> > Hey! >> > >> > In our past we had a couple of discussions about whether we should or >> should not use Optionals [1][2]. The main argument against it was >> performance. >> > >> > On one hand we risk additional object allocation (the Optional itself) >> and wrong inlining decisions taken by C2 compiler [3]. On the other hand we >> all probably "feel" that both of those things shouldn't be a problem and >> should be optimized by C2. Another argument was the Optional's doesn't give >> us anything but as I checked, we introduced nearly 80 NullPointerException >> bugs in two years [4]. So we might consider Optional as a way of fighting >> those things. The final argument that I've seen was about lack of higher >> order functions which is simply not true since we have #map, #filter and >> #flatmap functions. You can do pretty amazing things with this. >> > >> > I decided to check the performance when refactoring REST interface. I >> created a PR with Optionals [5], ran performance tests, removed all >> Optionals and reran tests. You will be surprised by the results [6]: >> > >> > Test case >> > With Optionals [%] Without Optionals >> > Run 1 Run 2 Avg Run 1 Run 2 Avg >> > Non-TX reads 10 threads >> > Throughput 32.54 32.87 32.71 31.74 34.04 32.89 >> > Response time -24.12 -24.63 -24.38 -24.37 -25.69 -25.03 >> > Non-TX reads 100 threads >> > Throughput 6.48 -12.79 -3.16 -7.06 -6.14 -6.60 >> > Response time -6.15 14.93 4.39 7.88 6.49 7.19 >> > Non-TX writes 10 threads >> > Throughput 9.21 7.60 8.41 4.66 7.15 5.91 >> > Response time -8.92 -7.11 -8.02 -5.29 -6.93 -6.11 >> > Non-TX writes 100 threads >> > Throughput 2.53 1.65 2.09 -1.16 4.67 1.76 >> > Response time -2.13 -1.79 -1.96 0.91 -4.67 -1.88 >> > >> > I also created JMH + Flight Recorder tests and again, the results >> showed no evidence of slow down caused by Optionals [7]. >> > >> > Now please take those results with a grain of salt since they tend to >> drift by a factor of +/-5% (sometimes even more). But it's very clear the >> performance results are very similar if not the same. >> > >> > Having those numbers at hand, do we want to have Optionals in >> Infinispan codebase or not? And if not, let's state it very clearly (and >> write it into contributing guide), it's because we don't like them. Not >> because of performance. >> > >> > Thanks, >> > Sebastian >> > >> > [1] http://lists.jboss.org/pipermail/infinispan-dev/2017-March/ >> 017370.html >> > [2] http://lists.jboss.org/pipermail/infinispan-dev/2016-August/ >> 016796.html >> > [3] http://vanillajava.blogspot.ro/2015/01/java-lambdas-and-low- >> latency.html >> > [4] https://issues.jboss.org/issues/?jql=project%20%3D%20ISPN% >> 20AND%20issuetype%20%3D%20Bug%20AND%20text%20%7E%20% >> 22NullPointerException%22%20AND%20created%20%3E%3D%202015- >> 04-27%20AND%20created%20%3C%3D%202017-04-27 >> > [5] https://github.com/infinispan/infinispan/pull/5094 >> > [6] https://docs.google.com/a/redhat.com/spreadsheets/d/1oep6Was >> 0FfvHdqBCwpCFIqcPfJZ5-5_YYUqlRtUxEkM/edit?usp=sharing >> > [7] https://github.com/infinispan/infinispan/pull/5094#issuecomm >> ent-296970673 >> > -- >> > SEBASTIAN ŁASKAWIEC >> > INFINISPAN DEVELOPER >> > Red Hat EMEA >> > >> > >> > _______________________________________________ >> > infinispan-dev mailing list >> > infinispan-dev(a)lists.jboss.org >> > https://lists.jboss.org/mailman/listinfo/infinispan-dev >> > >> > _______________________________________________ >> > infinispan-dev mailing list >> > infinispan-dev(a)lists.jboss.org >> > https://lists.jboss.org/mailman/listinfo/infinispan-dev >> >> >> _______________________________________________ >> infinispan-dev mailing list >> infinispan-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/infinispan-dev > > -- > > SEBASTIAN ŁASKAWIEC > > INFINISPAN DEVELOPER > > Red Hat EMEA <https://www.redhat.com/> > <https://red.ht/sig> > > _______________________________________________ > infinispan-dev mailing list > infinispan-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/infinispan-dev > _______________________________________________ infinispan-dev mailing list infinispan-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev