Diagnosing high cpu?

1

My app doesn’t have too many concurrent users (maybe 20 max) but and usually the cpu usage is low (~15%) but sometimes the cpu will go very high (60-70%) and then not come down for a while.

I have Kadira APM but its hard to tell the causes - all my subs show high wait times and high observeChanges times (2-3s), e.g. -

coll : doctypes
selector : {"_id":{"$in":["RrGFesNqrX2RxZg25","8EMKYEaPZNAaiE7qb","ucPzrYJFvhXJFZbRK","fa5PNTPSu6v2XQHEv","2TXRPYFXmvg77KzxL","pPNXsrH8uvug3Hwbs","Nk4oxGJdvGT3Yropn","i8CgydDJMPNFKMyWu","k6g5vF8f9pmPXHXDk","7XBhXx3aF9e8iYFmJ","tPiC6KeAWKoGxAtKu","HMnDFX82FPYb7Mjp5","NTZqwWxhQe2oN2MSN","NonQP3pgqF8XS77Kq","W63bo7zJEPzgzyqKQ","DbT9ce7tRtatiuMNk","eDZWkFepXWd3vRnwo","jffvyNWepApmvdcjo","sESHyB249GAi5i6C6","jN4SF2kuY9GKf8HPS","sZqQTqWhz9WXsPZDD","jsT7mmsDMLwFf2ToF","QjcGTsWi4GF9c6d2j","pmKqrqfgZ4Sym4Tdk","yih8cnspgTND62BKc","omngBPmz3AyHNoRTb","MMrvYafWsB2PyeKxu","ancSkozjjPPWqBEGa","bBniMMCQsNqqhjmZG","N9ruiWCkGsiKgHKaW","C9sd2P5arMuHYNeg9","NjXoknWtsP3DCKFW4"]}}
func : observeChanges
cursor : true
oplog : true
wasMultiplexerReady : false
queueLength : 0
elapsedPollingTime : 0
noOfCachedDocs : 200

All the subs/queries are using oplog.

I cannot tell if the high cpu is due to meteor doing more work and the queries being slow, or vice versa. I also looked at my mongodb and its in single digit cpu’s with no load on it.

What can I do to debug this?

2

How to config your server? Mannually ?

3

You will probably need to do some profiling. Kadira APM used to have this built in so if you can still do that it would be best.

4

You could also use https://github.com/node-inspector/v8-profiler

5

Warning for Meteor 1.6 users: last time I looked they were having some problems with Node 8 and v8-profiler npm

6

Did you find anything to help diagnose the problem?

I’ve just landed in a similar situation. Everything has been running fine for a month or more and now today I’m getting spikes every so often (4 times in the last hour) at 100% CPU, lasting for about 30-40 seconds. The mlab diagnostics show nothing unusual - nothing that coincides anyway, the odd page fault here and there. And kadira just shows that a method took a long long time, not that it went into an infinite loop or anything, so a method that normally takes 2000ms is taking 120000ms !!! :disappointed_relieved:

I can’t confirm this but it did seem like a new connection coincided with the spikes. We’re only talking 15-20 connections total though, so hardly anything too stressful.

Any holistic ideas on how to see what the problem is would be much appreciated.

7

@marklynch I think I was experiencing the same issue. However, it’s very hard to replicate, and there are no errors in the logs.

I think the problem may have gone for me, and I’m wondering if it was due to the upgrade to Meteor 1.8.1.