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
