Pessimistic lock, the concept of optimistic lock

Pessimistic lock: as the name implies, it is very pessimistic, it refers to the data by the outside world (including other current transactions of the system

As well as from other transactions, as well as transactions from external systems) modifications are conservative, so the data is locked throughout the data processing. Pessimistic lock implementation often depends on the locking mechanism provided by the database. Typical is the FOR UPDATE statement.

Optimistic locking: compared with pessimistic locking, optimistic locking mechanism adopts a more relaxed locking mechanism.

Every time I go to get the data, I think that others will not change it, so it will not be locked, but when I update it, I will judge whether others have updated the data during the period. We can use mechanisms such as version number.