title: Why Hadoop need that amount of RAM?
body: <p>Hadoop containers needs RAM more that the data size itsef (I am using for testing 0.5GB size of data) actually doubles of it, why it is too much?</p>
  
  <p>And what is the concept of physical memory and virtual memory off containers: sometime you get exception like 100mb of 500mb in physical memory but 2.5Gb exceeds 2GB in virtual memory. Why hadoop is exceeding the virtual memory limit as long as 2 GB basically is enough to run the whole Operating System and to keep all my data in the RAM memory so why 2GB it is not enough?</p>