并发控制

事务

A transaction is the execution of a sequence of one or more operations (e.g., SQL queries) on a database to perform some higher-level function.

事务是在 DB 上执行一系列一个或多个操作，用来执行一些更加高级的功能。

Atomicity: All actions in the txn happen, or none happen.
Consistency: If each txn is consistent and the DB starts consistent, then it ends up consistent.
Isolation: Execution of one txn is isolated from that of other txns.
Durability: If a txn commits, its effects persist.