《Netty官方文件》基準測試
原文連結 譯者：lijunshu
Netty有一個模組叫’netty-microbench’，我們可以用他來執行一系列的微型基準測試。Netty-microbench是基於OpenJDK JMH構件的（HotSpot的推薦基準測試方案）。當你開始netty基準測試時，你不需要額外的依賴。
執行基準測試
你可以通過maven 命令列或者直接從IDE開始你的基準測試，如果以預設設定開始跑測試，你可以使用命令列mvn -DskipTests=false。我們設定skipTests=false 是因為我們不想以單元測試的方式去執行這些基準測試。
如果沒有問題，你將為看到JMH開始warmup然後基於fork數量來執行基準測試，並提供給你漂亮的報告。你會看到一般情況下基準測試的結果如下。
# Fork: 2 of 2 # Warmup: 10 iterations, 1 s each # Measurement: 10 iterations, 1 s each # Threads: 1 thread, will synchronize iterations # Benchmark mode: Throughput, ops/time # Running: io.netty.microbench.buffer.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_1_0 # Warmup Iteration 1: 8454.103 ops/ms # Warmup Iteration 2: 11551.524 ops/ms # Warmup Iteration 3: 11677.575 ops/ms # Warmup Iteration 4: 11404.954 ops/ms # Warmup Iteration 5: 11553.299 ops/ms # Warmup Iteration 6: 11514.766 ops/ms # Warmup Iteration 7: 11661.768 ops/ms # Warmup Iteration 8: 11667.577 ops/ms # Warmup Iteration 9: 11551.240 ops/ms # Warmup Iteration 10: 11692.991 ops/ms Iteration 1: 11633.877 ops/ms Iteration 2: 11740.063 ops/ms Iteration 3: 11751.798 ops/ms Iteration 4: 11260.071 ops/ms Iteration 5: 11461.010 ops/ms Iteration 6: 11642.912 ops/ms Iteration 7: 11808.595 ops/ms Iteration 8: 11683.780 ops/ms Iteration 9: 11750.292 ops/ms Iteration 10: 11769.986 ops/ms Result : 11650.238 ±(99.9%) 229.698 ops/ms Statistics: (min, avg, max) = (11260.071, 11650.238, 11808.595), stdev = 169.080 Confidence interval (99.9%): [11420.540, 11879.937]
最終，你的測試結果看上去和這個相似，這個更多的取決於你的系統配置。
Benchmark Mode Samples Mean Mean error Units i.n.m.b.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_1_0 thrpt 20 11658.812 120.728 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_2_256 thrpt 20 10308.626 147.528 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_3_1024 thrpt 20 8855.815 55.933 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_4_4096 thrpt 20 5545.538 1279.721 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_5_16384 thrpt 20 6741.581 75.975 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledDirectAllocAndFree_6_65536 thrpt 20 7252.869 70.609 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledHeapAllocAndFree_1_0 thrpt 20 9750.225 73.900 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledHeapAllocAndFree_2_256 thrpt 20 9936.639 657.818 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledHeapAllocAndFree_3_1024 thrpt 20 8903.130 197.533 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledHeapAllocAndFree_4_4096 thrpt 20 6664.157 74.163 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledHeapAllocAndFree_5_16384 thrpt 20 6374.924 337.869 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.pooledHeapAllocAndFree_6_65536 thrpt 20 6386.337 44.960 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledDirectAllocAndFree_1_0 thrpt 20 2137.241 30.792 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledDirectAllocAndFree_2_256 thrpt 20 1873.727 41.843 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledDirectAllocAndFree_3_1024 thrpt 20 1902.025 34.473 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledDirectAllocAndFree_4_4096 thrpt 20 1534.347 20.509 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledDirectAllocAndFree_5_16384 thrpt 20 838.804 12.575 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledDirectAllocAndFree_6_65536 thrpt 20 276.976 3.021 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledHeapAllocAndFree_1_0 thrpt 20 35820.568 259.187 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledHeapAllocAndFree_2_256 thrpt 20 19660.951 295.012 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledHeapAllocAndFree_3_1024 thrpt 20 6264.614 77.704 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledHeapAllocAndFree_4_4096 thrpt 20 2921.598 95.492 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledHeapAllocAndFree_5_16384 thrpt 20 991.631 49.220 ops/ms i.n.m.b.ByteBufAllocatorBenchmark.unpooledHeapAllocAndFree_6_65536 thrpt 20 261.718 11.108 ops/ms Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 993.382 sec - in io.netty.microbench.buffer.ByteBufAllocatorBenchmark
你也可以直接從IDE執行基準測試。如果你匯入了netty的最頂層專案，開啟子專案microbench到子目錄src/test/java/io/netty/microbench 。在buffer子目錄，你可以像其它JUnit測試一樣執行ByteBufAllocatorBenchmark 。主要的區別就是，你可以一下子執行全部的基準測試，而不是去一個個的執行每一個基準測試。如果maven一樣，你可以在控制檯看到同樣的輸出。
編寫基準測試
雖然編寫基準測試不是太麻煩，但是卻不一定編寫的正確。這不是因為microbench專案很難使用，而是因為你很難去避免一些常用的陷阱。因此，JMH提供了有用的annotation和特性來幫助你避免大多數的陷阱。為此，你需要使你的基準繼承自AbstractMicrobenchmark，AbstractMicrobenchmark能保證以JUnit預設參賽的方式執行。
public class MyBenchmark extends AbstractMicrobenchmark {
}
下一步是建立一個方法以@GenerateMicroBenchmark 標註，然後給他一個合適的方法名。
@GenerateMicroBenchmark
public void measureSomethingHere() {
}
看這些樣例是很好的主意能啟發你如何去寫JMH測試。你也可以看下JMH主要作者的一些座談。
定製執行引數
預設的AbstractMicrobenchmark配置是
- Warmup次數 10
- 測試次數 10
- Fork數量 2
這些配置可以通過系統配置在執行的時候做配置
mvn -DskipTests=false -DwarmupIterations=2 -DmeasureIterations=3 -Dforks=1 test
需要注意通常並不建議跑測試時，用較少的迴圈次數，但是較少的次數有助於確認基準測試時工作的，在確認結束後，再執行大量的基準測試。
@Warmup(iterations = 20)
@Fork(1)
public class MyBenchmark extends AbstractMicrobenchmark {
}
這可以以方法級別或者類級別來執行基準測試，命令列的引數會覆蓋annotation上的引數。
ebay staff software engineer, working for software development 10+ years for electronic payment and e-commerce, interested in software design, development and new technology.