另外 koa 2.0 即将发布，真是一个好消息！
https://github.com/nodejs/node/blob/master/doc/changelogs/CHANGELOG_V7.md#7.6.0
This release contains v8 5.5
Async functions
In 5.5, V8 ships JavaScript ES2017 async functions, which makes it easier to write code that uses and creates Promises. Using async functions, waiting for a Promise to resolve is as simple as typing await before it and proceeding as if the value were synchronously available - no callbacks required. See this article for an introduction.
Here’s an example function which fetches a URL and returns the text of the response, written in a typical asynchronous, Promise-based style.
function logFetch(url) {
return fetch(url)
.then(response => response.text())
.then(text => {
console.log(text);
}).catch(err => {
console.error('fetch failed', err);
});
}
Here’s the same code rewritten to remove callbacks, using async functions.
async function logFetch(url) {
try {
const response = await fetch(url);
console.log(await response.text());
} catch (err) {
console.log('fetch failed', err);
}
}
Performance improvements
V8 5.5 delivers a number of key improvements in memory footprint.
Memory
Memory consumption is an important dimension in the JavaScript virtual machine performance trade-off space. Over the last few releases, the V8 team analyzed and significantly reduced the memory footprint of several websites that were identified as representative of modern web development patterns. V8 5.5 reduces Chrome’s overall memory consumption by up to 35% on low-memory devices (compared to V8 5.3 in Chrome 53) due to reductions in the V8 heap size and zone memory usage. Other device segments also benefit from the zone memory reductions. Please have a look at the dedicated blog post to get a detailed view.
然而v8已经撸到5.7了, 总算async/await 能有个4倍左右的提升， 之前的本地测试 Node 7.4的koa2 async/await 比 express还稍差一点(10~25中间件)，希望等用上5.7后能赶上koa1吧
https://v8project.blogspot.sg/2017/02/v8-release-57.html
v8 5.5 实现了内存占用的一些关键优化 内存占用高是JS虚拟机实现高性能的一个重要取舍。在之前几个版本中，V8团队分析并显著降低了一些应用现代web开发模式的代表性网站的内存占用。v8 5.5版 通过降低heap size 和zone memory usage，降低了chrome在低内存设备至多35%的总体内存消耗（和chrome 53的v8 5.3相比）。其他设备也能从更低的zone memory usage获益
这俩名词想不出合适的翻译。。慢慢啃原文吧 heap size & zone memory usage 是啥 v8 heap size
@i5ting 下午测试了下7.6.0 t8 c50 mw10/15/20/25，koa2 async 达到koa2的2/3，已经超越express和koa1 主要考虑到实际使用中边缘情况较少，所以没算<10和>30的情况 koa2 async/await
Running 3s test @ http://localhost:3333
8 threads and 50 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 5.25ms 1.88ms 35.58ms 95.94%
Req/Sec 1.17k 186.09 1.32k 93.55%
28941 requests in 3.10s, 4.17MB read
Requests/sec: 9321.19
Transfer/sec: 1.34MB
koa2
Running 3s test @ http://localhost:3333
8 threads and 50 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 3.61ms 1.60ms 34.12ms 95.88%
Req/Sec 1.72k 271.24 1.90k 93.55%
42541 requests in 3.10s, 6.13MB read
Requests/sec: 13711.05
Transfer/sec: 1.97MB
koa1
Running 3s test @ http://localhost:3333
8 threads and 50 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 5.36ms 1.67ms 34.49ms 93.26%
Req/Sec 1.14k 242.39 2.91k 95.47%
27602 requests in 3.10s, 3.97MB read
Requests/sec: 8897.56
Transfer/sec: 1.28MB
express
Running 3s test @ http://localhost:3333
8 threads and 50 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 6.10ms 1.91ms 37.10ms 91.94%
Req/Sec 1.00k 181.97 1.81k 91.43%
24442 requests in 3.10s, 4.90MB read
Requests/sec: 7874.38
Transfer/sec: 1.58MB
