Simple Locking:

• Two main types of locks can be requested:
  • Shared lock: Read lock i.e. Any other TX can read but not write
  • Exclusive lock: Write lock i.e. No other TX can read or write

Multiple Locking:

• Two Phase Locking (2PL) is a concurrency control method that guarantees serializability.
  • A Growing/Expanding/First Phase: locks are acquired and no locks are released.
  • A Shrinking/Contracting/Second Phase: locks are released and no locks are acquired.

Reference

https://stackoverflow.com/questions/7713049/read-locks-and-write-locks