Lock questions

Hello,
i've been reading the README file in the lmgr folder (in src/backend/storage/lmgr/) and i have a couple of questions
aboutlocks: 
  - What's the difference between the Lightweight Locks (LWLocks) and the Regular locks (Heavyweight Locks)? For
example,if i do a query and it needs a lock, would  it be a lightweight one or a regular one? 

  - There are two lock methods, DEFAULT and USER. Where can I get more information about them? In the README file it
saysthat "USER locks are non-blocking", how could this be? 

Thank you very much!


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