title: nodejs callback async calls maximum limit
body: <p>I'm new new to nodejs and want to have some clarity about the callstack. What my application does is read messages from SQS and upload asynchronously to different datasources like dynamo,  mysql,stream etc... The problem here is using multiple workers we can receive in parallel 20/30 msgs at a time and will do async calls to upload.Since the operation is slower to upload and receive the callback, I doubt the event queue in nodejs will be filled with async calls while I make all upload async calls in a short time. So, I have two questions</p>
  
  <ol>
  <li><p>What is the maximum capacity of event loop and how many async calls can lie in event loop at once.</p></li>
  <li><p>How to control the concurrency and get the details of load and calculate wait time needed for next upload async call.</p></li>
  </ol>
  
  <p>ps: Assuming I can read 80000 msgs in 10 mins, I can't make 80000 parallel async upload IO calls and queue them in nodejs event loop. Please help me understand this. </p>