title: primary indexes Vs secondary indexes: performance differences
body: <p>I've got a little question: what is the difference in performance between the primary and secondary indexes? what causes this difference?</p>
  
  <p>I'm googling around, and I've seen that secondary indexes are stored in another table, so this slows down all operations.. but there are some other reasons that justify this decrease in performance?</p>
  
  <p>Thanks a lot</p>