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I want to enable thread-like storage for my express app which handles ~100 to 300 API calls per minute. I've played with continuation-local-storage (and cls-hooked since I'm on Node 8.9.0) but the CPU spikes are very high (500x normal and dont level) and have crashed the server. The endpoints mostly do CPU light synchronous computation (e.g. calling API's, doing lookups, rarely I/O intensive tasks)

Do anyone have experience running csl at scale with Express?

E Fleischman
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  • cls-hooked uses async_hooks internally for node version 8+. This article may be worth a glance, as it talks about the performance impact: https://dzone.com/articles/beware-the-performance-cost-of-async-hooks-node-8 – benbotto Mar 01 '19 at 03:49

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Recently I was playing around with cls-rtracer, my small library for Express and Koa. This library is just a collection of lightweight middlewares built on top of cls-hooked. So basically I was testing the footprint of cls-hooked (and Async Hooks API, as I was using version 8 of Node.js).

I've implemented a very simple Express app and tested it on my machine with and without CLS. The scenario with CLS was the following:

  • On each request an id was generated with uuid/v4 and then stored in CLS. This was done by the cls-rtracer middleware.
  • In the route middleware, there was some logging done with winston, a logger library. The library was configured to obtain the request id from CLS and append it for each log entry.

The load was generated by ab utility. I was using Windows 10 and Node.js 10, but also tested on a Ubuntu VM with Node.js 8 and got similar results.

As the result, I got about 10-15% RPS (request per second) degradation with request ids and CLS turned on. As for CPU utilization, I didn't see any major difference, like sudden spikes, between these two scenarios.

I've published my test app as a gist: https://gist.github.com/puzpuzpuz/3c2a36ca0835906ad50dbd22c72df974

Looks like a late response, but it may help someone in future. These scenarios should be quite close to real-world apps.

2020 update. Starting from v12.7.0 Node.js includes AsyncLocalStorage API. This CLS core API has significantly lower footprint when compared with cls-hooked and other CLS libraries.

Andrei Pechkurov
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  • A small follow-up: Node versions were v10.13.0 (on Windows) and v8.12.0 (on Ubuntu). I'm curious if this, better behavior in comparison with results from the topic starter, is about improvements in async_hooks performance or the reason is somewhat different. – Andrei Pechkurov Dec 06 '18 at 08:45
  • N.B. `cls-hooked` uses `AsyncLocalStorage` in Node > 8 – malix Jan 25 '23 at 23:27