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

Sebastian Laskawiec slaskawi at redhat.com
Thu May 25 04:00:09 EDT 2017


Adding part of your email from REST refactoring thread:

Looking into the code, without considering performance at all, I think
> that you've become too ecstatic about Optionals. These should be used as
> return types for methods, not a) parameters to methods nor b) fields.
> This is a misuse of the API, according to the authors of Optionals in
> JDK. Most of the time, you're not using optionals to have fluent chain
> of method invocations, so -100 to that.
>

I'm sorry I'm not picking up the discussion about REST refactoring PR since
it has been already merged. Plus I'm not planning to do any Optionals
refactoring as long I don't have a clear vision how we'd like to approach
it.

But I'm actually very happy you touched the use case topic. So far we were
discussing advantages and disadvantages of Optionals and we didn't say much
about potential use cases (Katia, Dan, Galder and Sanne also touched a
little this topic).

Indeed, Stephen Colebourne [1] mentions that it should be used as method
return types:
"My only fear is that Optional will be overused. Please focus on using it
as a return type (from methods that perform some useful piece of
functionality) Please don't use it as the field of a Java-Bean."

Brian Goetz also said a few words on Stack Overflow about this [2]:
"For example, you probably should never use it for something that returns
an array of results, or a list of results; instead return an empty array or
list. You should almost never use it as a field of something or a method
parameter.
I think routinely using it as a return value for getters would definitely
be over-use."

So if we want to be really dogmatic here, we wouldn't be able to use
Optionals in fields, method parameters, and getters. Please note that I'm
blindly putting recommendations mentioned above into code. As it turns out
we can use Optionals anywhere, except method returning some objects which
are not getters.

It is also worth to say that both gentlemen are worried that Optionals
might be overused in the libraries.

On the other hand we have Oracle's tutorials which use Optionals as a
fields [3]:
"public class Soundcard {
  private Optional<USB> usb;
  public Optional<USB> getUSB() { ... }
}"
and say no word about recommendations mentioned in [1] and [2].

Also many libraries (like Jackson, Hibernate validator) support Optionals
as fields [5]. So it must be somewhat popular use case right?

I think my favorit reading about Optional use cases is this [6]. So the
author suggests to use Optionals as a return types in API boundaries but
use nulls inside classes. This has two major advantages:

   - It makes the library caller aware that the value might not be there
   - The returned Optional object will probably die very soon (a called
   will probably do something with it right away)

An example based on Oracle's tutorial would look like this (following this
recommendation):
"public class Soundcard {
  private USB usb;
  public Optional<USB> getUSB() { return Optional.ofNullable(usb); }
}"

I think it hits exactly into Katia's, Sanne's, Dan's and Galder's points.

What do you think?

[1] http://blog.joda.org/2014/11/optional-in-java-se-8.html
[2]
https://stackoverflow.com/questions/26327957/should-java-8-getters-return-optional-type/26328555#26328555
[3]
http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html
[4] http://blog.joda.org/2015/08/java-se-8-optional-pragmatic-approach.html
[5] http://dolszewski.com/java/java-8-optional-use-cases/
[6] http://blog.joda.org/2015/08/java-se-8-optional-pragmatic-approach.html

On Wed, May 24, 2017 at 4:56 PM Radim Vansa <rvansa at redhat.com> wrote:

> I haven't checked Sebastian's refactored code, but does it use Optionals
> as a *field* type? That's misuse (same as using it as an arg), it's
> intended solely as method return type.
>
> Radim
>
> On 05/23/2017 05:45 PM, Katia Aresti wrote:
> > Dan, I disagree with point 2 where you say "You now have a field that
> > could be null, Optional.empty(), or Optional.of(something)"
> >
> > This is the point of optional. You shouldn't have a field that has
> > these 3 possible values, just two of them = Some or None. If the field
> > is mutable, it should be initialised to Optional.empty(). In the case
> > of an API, Optional implicitly says that the return value can be
> > empty, but when you return a "normal" object, either the user reads
> > the doc, either will have bugs or boilerplate code defending from the
> > possible null value (even if never ever this API will return null)
> >
> > :o)
> >
> > Cheers
> >
> >
> >
> > On Tue, May 23, 2017 at 3:58 PM, Dan Berindei <dan.berindei at gmail.com
> > <mailto:dan.berindei at gmail.com>> wrote:
> >
> >     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 at redhat.com <mailto:slaskawi at redhat.com>> 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
> >         <
> https://github.com/infinispan/infinispan/tree/master/documentation/src/main/asciidoc/contributing
> >
> >
> >         On Mon, May 22, 2017 at 6:36 PM Galder Zamarreño
> >         <galder at redhat.com <mailto:galder at redhat.com>> 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 at infinispan.org <mailto:sanne at infinispan.org>> 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 at redhat.com <mailto:slaskawi at redhat.com>> 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
> >             <
> http://lists.jboss.org/pipermail/infinispan-dev/2017-March/017370.html>
> >             > [2]
> >
> http://lists.jboss.org/pipermail/infinispan-dev/2016-August/016796.html
> >             <
> http://lists.jboss.org/pipermail/infinispan-dev/2016-August/016796.html>
> >             > [3]
> >
> http://vanillajava.blogspot.ro/2015/01/java-lambdas-and-low-latency.html
> >             <
> 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
> >             <
> 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
> >             <https://github.com/infinispan/infinispan/pull/5094>
> >             > [6]
> >
> https://docs.google.com/a/redhat.com/spreadsheets/d/1oep6Was0FfvHdqBCwpCFIqcPfJZ5-5_YYUqlRtUxEkM/edit?usp=sharing
> >             <
> https://docs.google.com/a/redhat.com/spreadsheets/d/1oep6Was0FfvHdqBCwpCFIqcPfJZ5-5_YYUqlRtUxEkM/edit?usp=sharing
> >
> >             > [7]
> >
> https://github.com/infinispan/infinispan/pull/5094#issuecomment-296970673
> >             <
> https://github.com/infinispan/infinispan/pull/5094#issuecomment-296970673>
> >             > --
> >             > SEBASTIAN ŁASKAWIEC
> >             > INFINISPAN DEVELOPER
> >             > Red Hat EMEA
> >             >
> >             >
> >             > _______________________________________________
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> >             >
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> >
> >
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> >
> >         --
> >
> >         SEBASTIANŁASKAWIEC
> >
> >         INFINISPAN DEVELOPER
> >
> >         Red HatEMEA <https://www.redhat.com/>
> >
> >         <https://red.ht/sig>
> >
> >
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> --
> Radim Vansa <rvansa at redhat.com>
> JBoss Performance Team
>
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-- 

SEBASTIAN ŁASKAWIEC

INFINISPAN DEVELOPER

Red Hat EMEA <https://www.redhat.com/>
<https://red.ht/sig>
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