Database transaction level

Transaction Four Properties acid

atomicity Atomic Nature

Consistency consistency

Isolation isolation

Durability Persistence

The database has three problems with high concurrency, with concurrent transactions, A, A, a

Dirty read: A read B uncommitted data,

Non-repeatable READ: A first query data, b update data and submit, a second query, read the updated B data, resulting in two queries inconsistent

Magic read: A query the database, b new or delete data, a second query data inconsistency

To address these three issues, the database sets four isolation levels

Read_uncommited: Allow dirty read, non-repeatable read, Phantom read

Read_commited: Dirty reads are not allowed

Repeatable_read: Dirty read not allowed, non-repeatable read

SERIALIZABLE: It's not allowed.

Database transaction level