Speed Of Stream Questions Java,Sterling Center Console Bass Boat Pdf,What Does Excursion Boat Mean Problems - For Begninners
Batman battle. If we pit sequential streams against regular for-loops, which one comes out faster? After some careful benchmark tests, Angelika Langer quesions us which is fastest, and why must be careful to make judgements. A while ago I qhestions about the performance of Java 8 streams in this forum, showed a couple of figures that illustrate certain aspects of the performance characteristics of streams, and explained why these results are plausible.
In one of these benchmark experiments we compared the performance of sequential streams and regular for- loops. In the context in which we did the measurement the for-loop was approximately 15 times faster than the corresponding sequential stream.
Reactions to this performance comparison vary from surprise to utter disbelief. Some people even conclude that streams are too slow to be useful.
Od any case, it is not helpful. When you benchmark, then you usually benchmark a lot and never rely speed of stream questions java a single set of figures � neither did we.
So, let us put the results into perspective. For the benchmark that illustrated the for- loop as 15 times faster as the corresponding sequential stream we used an int-array filled withrandom integral values. In this array we searched for the maximum value.
As the counterpart to an int[] we used a sequential primitive IntStream :. The results on our outdated hardware dual core, no dynamic overclocking with proper warm-up and questios it takes to produce halfway reliable benchmark figures were this:.
The for -loop is substantially faster that the sequential stream. We ran the same benchmark on a more modern hardware with 4 virtual cores and found a slowdown factor of 4. He came up with a slowdown factor of 4. As is expected, a different context yields different results.
The results were:. Again, the for- loop is faster that the sequential stream operation, but the difference on an ArrayList is not nearly as significant as it was on an array. Is any of it surprising? No, actually not, if you think of it. In this benchmark we invest a lot to retrieve half a million values from a sequence in memory and once we get hold of the values we perform a petty pair-wise comparison of two integral values, which after JIT compilation is barely more than one assembly instruction.
For this reason, the benchmark results are dominated by the cost of memory access and the cost of iteration. As the speed of memory access is hardware-dependent the results vary from platform to platform. This explains the different slowdown factors on different platforms.
The fact that the for-loop beats the sequential stream in our benchmark is not surprising. We deliberately picked an extreme situation, which represents an end of a spectrum. Actually, there are several spectra involved. As you can tell now, a questinos over an int[] searching for the maximum element benefits from the JIT-friendly loop and the cache-friendly primitive array with no CPU-intensive activities that would mask any of these advantages.
Of course the for-loop shines under these circumstances. How likely is it that THE performance critical speed of stream questions java in our application is a loop over a primitive-type array with barely any CPU activity?
Not very likely, I would say. We did it because it is a piece of the puzzle. It is a demarcation line and represents a certain extreme situation against which you can compare other scenarios involving streams. The for-loop over an int[] is the best-case scenario: if a stream usage is as fast as that then it is really good.
If the for-loop over an int[] searching for the maximum element is one end of a spectrum, what are the performance figures for the other end of the spectrum.
Let us look into the aforementioned Speed of stream questions java use case. It was measured on the out-dated hardware that we used for the slowdown factor of Also, we got impatient and reduced the size of the sequences by a factor of 50 fromto 10, ; it simply took too long to run the benchmark withelements. Looking at the resulting figures we conclude that the for-loop is still a little faster than the sequential stream, but the difference is no longer substantial.
The difference still is statistically significant if you run the samples through a t-testbut for all practical purposes it is negligible. Now we proved the opposite of what our previous benchmark suggested: there strean hardly any difference in the performance of sequential streams and for-loops.
In this benchmark, we do not simply compare sequence questiohs to each other as soon as we get hold of. Instead we stuff each sequence element into the mysterious slowSin method that calculates the sine value before we compare.
The slowSin method is indeed very slow. It is a non-public method taken from the Apache Commons Mathematics Library ACMLwhere it is used to fill a table of sine values that are later used for the public sin method, which performs a fast interpolation based on the table values see class FastMathCalc.
It calculates the sine value by means of a Taylor approximation, quesgions is a calculation that keeps the CPU very, very busy. No data need to be loaded from memory, except the initial parameter, and the CPU is questons occupied with itself and its registers for quite a bit of time.
Very different from the petty pair-wise comparison the CPU had to perform in the previous benchmark. Under these circumstances the benchmark results are dominated by the availability and speed of the CPU and all speed of stream questions java aspects such as cache misses and JIT-compiled loops become insignificant.
Again: How likely is it that THE performance critical activity in our application is a loop over a primitive-type array with a CPU-intensive activity such as a Taylor approximation? It might be for some applications, but it is not extremely likely for. Why did we measure it then? Because it is another piece of the puzzle � on speed of stream questions java opposite end of a spectrum. The point to take home is: a sequential stream can be significantly slower than a for-loop in certain situations, while there is no substantial performance difference in other situations.
In most situations sequential streams are somewhat slower than for-loops; in very special situations they are substantially slower, but in general the speed of stream questions java difference will be tolerable � especially if you consider that in practice most stream sizes are in the magnitude of dozens of elements, not hundreds of thousands of elements like in speed of stream questions java benchmark.
Even a slowdown factor of 15 does not hurt if you loop over a handful of elements. Who cares? Questioms performance difference is only relevant for hot spots in your application, speed of stream questions java. First you need proof that there is a performance bottleneck e. Angelika Langer.
Speed of stream questions java Posts by Angelika Langer. November 26, Angelika Langer. Stopwatch image via Shutterstock. Both ends of a spectrum For the benchmark that illustrated the for- loop as 15 times faster as the corresponding sequential stream we used an int-array filled withrandom integral values.
The results were: ArrayList, for-loop : 6. We compared for-loops to streams. Loops are JIT-friendly. This is one end of a spectrum: a JIT-friendly, highly optimizable access to the sequence elements. As opposed to streams. Speed of stream questions java a stream means calling into a major framework, which inevitably adds overhead.
A JIT compiler will eliminate the overhead to speed of stream questions java extent, but usually not completely. By questioms way, speed of stream questions java are sequential streams that are by far slower than the ArrayList in our benchmark. We will get to this later. No surprise. We compared sequences of primitive type steam to sequences of reference type elements.
A collection of reference type elements, even if it is an array-based collection such as ArrayListhas little chance to be cached efficiently. Every individual access to a sequence element requires dereferencing a pointer and reaching out into memory � which means yet another cache miss. Clearly, a for-loop over an int[] is on the cache-friendly side speed of stream questions java will win performance-wise compared to a sequential reference stream.
No surprise here. We compared a light-weight element usage to Questiond speed of stream questions java usage. More precisely, we compared a pair-wise comparison when looking for the maximum value with a Taylor approximation jav sine values.
We will get to sine values in a minute. Conclusions The point to take home is: a sequential stream can be significantly slower than a for-loop in certain situations, while there is no substantial performance difference in other situations. Be the first to share this article with your network! Inline Feedbacks. Join us in London or Online! Speed of stream questions java Posts.
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