title: Sql isolation levels, Read and Write locks
body: <p>A bit lame question but I got confused... 
  Difference between isolation levels as far as I understood is how they managed their locks (<a href="http://en.wikipedia.org/wiki/Isolation_(database_systems)" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Isolation_(database_systems)</a>). So as mentioned in the article there are Read, Write and Range locks but there is no definition what they are itself.
  What are you allowed to do and what not. When I googled for it there was nothing concrete
  and instead I got confused with new terms like Pessimistic Lock an Optimistic Lock, Exclusive lock, Gap lock and so on. I'd be pleased if someone give me a short overview and maybe point me a good bunch materials to enlighten myself.</p>
  
  <p>My initial question which started the research of isolation levels was:</p>
  
  <p>What happens when I have concurrent inserts (different users of web app) into one table when my transactions isolation level is READ_COMMITED. Is the whole table locked or not?
  Or generally what happens down there :) ?</p>
  
  <p>Thanks in advance !</p>