check-logs-issue-3916.js

require('babel-register');

const fs = require('fs');
const readline = require('readline');

const rl = readline.createInterface({
  // This was a log file from production for a single NodeJS app instance.
  // It had 7 OOM crashes. After each crash the app was restarted.
  input: fs.createReadStream('/Users/kumar/Downloads/docker-addons-frontend.service.log'),
});

console.log('Processing log');

const stats = {
  lastElapsed: 0,
  highestElapsed: 0,
  heapOOM: 0,
  skipped: 0,
  total: 0,
};

// This means the app crashed.
const heapOOM = /JavaScript heap out of memory/;

const timeStampPrefix = /^[^{]+/;

var done = false;
var started = false;

rl.on('line', (line) => {
  if (heapOOM.test(line)) {
    stats.heapOOM += 1;
    if (stats.heapOOM === 1) {
      // This is when an OOM crash happens. The app gets restarted so we
      // start tracking the number of requests.
      started = true;
    }
    if (stats.heapOOM === 2) {
      // This is when the next OOM crash happens. We can stop
      // tracking the number of requests.
      done = true;
    }
    return;
  }

  if (!started) {
    return;
  }
  if (done) {
    return;
  }

  stats.total += 1;

  const fixedLine = line.replace(timeStampPrefix, '');
  let dataLine;
  try {
    dataLine = JSON.parse(fixedLine);
  } catch(e) {
    stats.skipped += 1;
    return;
  }

  if (dataLine.start && dataLine.elapsed) {
    stats.lastElapsed = dataLine.elapsed;
    if (dataLine.elapsed > stats.highestElapsed) {
      stats.highestElapsed = dataLine.elapsed;
    }
  }
});

rl.on('close', () => {
  console.log(stats);
});