CPU Usage spikes - how to identify problems

General
1

Hello,

my node-red sees huge (100%+) CPU usage spikes from time to time. I do have 100+ individual function nodes and > 25 flows, however none of those are complex or justify the cpu usage.

Do you have any hints how to identify the function node or the flow responsible for those?

Regards,
Dennis

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If you are running on Linux try htop, which will show you which processes are using resources.

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it is the node-red process - question beeing, how can identify the function within node-red, which is responsible for the high load.

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I don't think you can directly identify which function is problematic. Try eliminating functions systematically!

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Yeah, I'm in the process of that too, just trial and error. I'm actually moving flows over to a new instance since I can't figure out why my old one hangs all the time.

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Hey @deme,

Very interesting question!
Would be nice if you could measure the cpu of each Node-RED block, instead of having to use trial-and-error. But I'm not sure whether you can do that, because I 'think' it works like this:

  • A Node-RED block will execute some code (synchronous) => I think you could (somehow) measure the CPU usage required to execute this code.
  • But in that code other code could be called asynchronous => this code will be executed afterwards by the event loop => You would have to measure this CPU usage also, since it has been triggered originally by the Node-RED node.
  • And that previous asynchronous code, can again call another code snippet asynchronously.
  • And so on ...

So you would have to keep track somehow of all code that has been triggered by the Node-RED node, and then sum all those cpu usages to calculate the cpu usage of that Node-RED node. And this process needs to be repeated for all nodes in your flow. Then you would have a nice overview of how much cpu each of your Node-RED nodes uses.

But no idea how to measure that :woozy_face:
I assume you need a CPU profiler. For example if we have a look at the output of this (obsolete!!!) async-profile module:

image

It seems to me that it keeps track of all asynchronous calls, and at the end all cpu usages are aggregated. But I have never digged into NodeJs cpu profilers...

Bart

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Digging a bit deeper, apparently, this topic had been discussed / worked on before:

Has someone worked with one of these tools before?

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Don't forget this is all running in node.js... When it gets above a certain memory limit (--max-old-space) the garbage cleaner will kick in and try to reclaim the memory. On a small processor with other things going on, this can be quite aggressive and cause spikes. Possibly... or maybe something else.

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Swapping can also cause big spikes when running off an sd-card. So you should check and get rid of anything not really necessary. Obviously, you won't want to be running a desktop so make sure you stop any desktop related services.

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