Node Architecture and Performance Analysis

Node

Threads:
  It consists of intructions to be ran on a process in the cpu..It is a part of thread
  An OS schedular tells which threads should be processed
  
Process:
  An instance of a  computer program 
  A process can have multiple threads
  
Cores(cpu):
  A Cpu can execute more than one thread a time, this is called multi-threading or hyper-threading
  More the cpu cores number of threads can be executed increases
  
I/O Intesive Tasks
  
  - Refers to using file system and network connections
  - Async FileSytems,DNS are handled by worker pool in libuv

CPU Intensive Tasks
  
  -  Zlib, Crypto, Stringify, parse are handled by worker pool in libuv

NODE IS SINGLE THREADED::

  - Node uses only one thread to process the request given to it..
  - Node consist of EVENT LOOP 
  - Node.js has two types of threads: one Event Loop and k(logical cores) Workers. 
    => The Event Loop is responsible for JavaScript callbacks and non-blocking I/O, and 
    => Worker executes C++code(libuv)that completes an asynchronous request,blocking I/O and CPU-intensive work
  
EventLoop::

  - Event Loop is a single thread
  - Every loop is a tick (can be explicitly called by process.tick() or setImmediate() that can run in next tick)
  - Order of executions::
      - Timers: this phase executes callbacks scheduled by setTimeout() and setInterval().
      - Pending callbacks or OS tasks: executes I/O callbacks deferred to the next loop iteration (Like listening to a port,if a req comes in it is called back). => THIS IS WERE THE WORKER POOL STUFFS ARE CALLED AND ACCESSED
      - Idle, prepare: only used internally. (wait for pending tasks to be completed or new ones to come in)
      - Poll: retrieve new I/O events; execute I/O related callbacks (almost all with the exception of close callbacks, the ones scheduled by timers, and setImmediate()); node will block here when appropriate.
      - Check: setImmediate() callbacks are invoked here.
      - Close callbacks: some close callbacks, e.g. socket.on('close', ...)

Worker Pool::
      - It handles all the io and cpu intensive tasks of node js from the event loop
      - It has default 4 threads(default)
      - process.env.UV_THREADPOOL_SIZE = 1024 max
      
Increase the Capability of node app::

  1) ulimit -n 999999 => increase number of open sockets
  2) –nouse-idle-notification => remove gc()
  3) –expose-gc => specify gc()
  4) –max-old-space-size=8192  => increase heap size  

Increase the Potential Of Node::

  Use Cluster module => cluster.fork() for as many logical cores available