What are optimistic and pessimistic locks for databases? How do you do that? Usage scenarios?

Pessimistic locking

By default, conflicts occur, and records are locked at the end of the query until unlocked at the end of the transaction; The principle is to use a lock in the database.

Optimistic locking

By default, no conflicts occur and data integrity is checked only when a transaction is committed; The implementation principle is the version number mechanism or CAS algorithm.

Usage scenarios

Use less optimistic locks for write operations and more pessimistic locks for write operations.