Most loggers write to streams in a risky way, here is a simple demonstration, and way to avoid the issue.

how-to-log.js

var fs = require('fs')
var http = require('http')

var count = 0

// using fs.createWriteStream directly will cause massive memory and cpu ussage
// var log = fs.createWriteStream('test.log')
// if you want to make your computer feel bad, replace this with the line above
var log = new Logger('test.log')

// a simple server that sends an empty response and logs a message.
http.createServer(function(req, res) {
  count += 1
  res.end()
  log.write('handled a request\n  ')
}).listen(9876)

// make a few simultainous requests to our server
for(var i = 0; i < 10; ++i) {
  makeRequest()
}

// make a requests, on response, setup anotger request
function makeRequest() {
  http.request('http://localhost:9876', function(res) {
    res.on('end', makeRequest)
    res.resume()
  }).end()
}

// log out some performance stats
setInterval(function() {
  console.log(count, 'requests/s.', 'memory ussage:', process.memoryUsage())
  count = 0
}, 1000)


// A simple logger that ovoids this issue
function Logger(path) {
  if(!(this instanceof Logger)) {
    return new Logger(path)
  }

  // this will overwrite the previous file. Appending
  // in this test is an unnessisary waist of disk space
  this.stream = fs.createWriteStream(path)

  // a place to store logs if the stream cant keep up
  this.buffer = ''

  // we will pause if the stream falls behind
  this.paused = false
}

Logger.prototype.write = function write(msg) {
  var logger = this

  // if we are paused, add message to the buffer, we can deal with it later
  if(logger.paused) {
    return logger.buffer += msg
  }

  // writing to a stream returns a boolean, if it returns false we should pause
  logger.paused = !logger.stream.write(msg)

  // if we paused, wait for the stream to catch up
  if(logger.paused) {
    logger.stream.once('drain', function() {
      // reset the state, then log out our accumulated messages
      var msg = logger.buffer
      logger.paused = false
      logger.buffer = ''
      logger.write(msg)
    })
  }
}