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"top" command for Node apps

The idea is to be able to quickly see the heaviest currently running Node functions using a single command in the terminal just like with "top" for regular processes. Another major point is only attaching the inspector for the time of the profiling so the tool can be always available in a production server without causing any overhead.

Once this is enabled there's no need to restart the app with "--profile" flag so any unexpected high CPU usage can be debugged more easily.

Usage - with no code changes required(Linux only)

npm i -g ntop
ntop inject 12345 // where 12345 is the process id
ntop 12345

Usage with includes in a project

npm i ntop

Add to the script to enable communication with CLI tool

const ntop = require('ntop')
ntop()

Then run the CLI. It will find all processes enabled for ntop communication

npx ntop

You'll see a list of ntop-enabled Node processes and their corresponding PIDs for convenience. Now you can see the list of functions for any process with

npx ntop 12345

Example output:

  • (garbage collector) | 11.703ms |
  • utils.bulkPreparePacket | 1.53ms | file:///home/app/src/Utils.js:91:26
  • (anonymous) | 1.181ms | evalmachine.:3:14
  • (anonymous) | 1.126ms | file:///home/app/node_modules/lodash/lodash.js:1223:19

Custom sampling time 5s

npx ntop 12345 5000

Verbose output showing breadcrumbs i.e. to see what called (anonymous)

npx ntop 12345 5000 -v

Example output with "breadcrumbs":

  • (garbage collector) | 4.191ms |

  • utils.bulkPreparePacket | 3.034ms | file:///home/app/src/Utils.js:91:26
    < prepareBulkData < (anonymous) < update < emit < update < processTick < (anonymous) < listOnTimeout < processTimers

  • (anonymous) | 2.574ms | evalmachine.:3:14
    < listOnTimeout < processTimers

  • prepareBulkData | 1.516ms | file:///home/app/src/controllers/Map.js:672:17
    < (anonymous) < update < emit < update < processTick < (anonymous) < listOnTimeout < processTimers

  • hasCallback | 1.141ms | file:///home/app/src/Scripting.js:271:13
    < update < emit < update < processTick < (anonymous) < listOnTimeout < processTimers

Experimental flame chart

npx ntop 12345 5000 -f

"Flame chart" (initial experiment):

  • (root) 3056.191ms
    -- processTimers 0.661ms
    --- listOnTimeout 0.661ms
    ---- (anonymous function) 0.661ms
    ----- processTick 0.661ms
    ------ queueNextAction 0.661ms
    ------- setImmediate 0.661ms
    -------- Immediate 0.661ms
    --------- initAsyncResource 0.661ms
    -- processTimers 1.305ms
    --- listOnTimeout 1.305ms
    ---- (anonymous function) 1.305ms
    ----- processTick 1.305ms
    ------ update 1.305ms
    ------- emit 1.305ms
    -------- update 1.305ms
    --------- (anonymous function) 1.305ms
    -- (garbage collector) 2.185ms
    -- processTimers 1.118ms
    --- listOnTimeout 1.118ms
    ---- (anonymous function) 1.118ms
    ----- processTick 1.118ms
    ------ update 1.118ms
    ------- emit 1.118ms
    -------- update 1.118ms
    --------- (anonymous function) 1.118ms
    ---------- prepareBulkData 1.118ms
    ----------- utils.bulkPreparePacket 1.118ms
    -- processTimers 1.471ms
    --- listOnTimeout 1.471ms
    ---- (anonymous function) 1.471ms
    ----- processTick 1.471ms
    ------ update 1.471ms
    ------- emit 1.471ms
    -------- update 1.471ms
    --------- (anonymous function) 1.471ms
    ---------- prepareBulkData 1.471ms
    ----------- utils.bulkPreparePacket 1.471ms
    ------------ preparePacket 1.471ms