What types of locks are there in PostgreSQL?

In PostgreSQL, there are several types of locks that ensure data consistency and manage concurrent access:

• Row-level locks:

  • FOR UPDATE — locks selected rows for updating.
  • FOR SHARE — locks rows for shared reading.

• Table-level locks:

  • ACCESS SHARE — lock for reading (SELECT).
  • ROW SHARE — lock for operations that modify rows (e.g., SELECT FOR UPDATE).
  • EXCLUSIVE and ACCESS EXCLUSIVE — locks that prevent access by other transactions.

• Advisory locks:

  • User-defined locks that can be used for synchronization at the application level.

Each lock has its own level and compatibility with other locks, allowing efficient management of parallelism.