Four characteristics of transactions (acid):

One 、 Atomicity （Atomicity）
In chemistry, atoms refer to basic particles that cannot be separated again , Atomicity in database emphasizes that transactions are an indivisible whole , After the transaction starts, all operations are either successful , All or nothing , It's impossible to stop in the middle . If there is an error during the execution of the transaction, it will be rolled back to the state before the start of the transaction , All operations will not have any impact on the database as if they did not happen .
Two 、 Uniformity （Consistency）
Transactions must transform the database from one consistent state to another , That is, a transaction must be in a consistent state before and after execution . Take money transfer , Suppose the user A And the user B The sum of the two is 5000, So no matter A and B How to transfer money between banks , Transfer several times , After the transaction ends, the sum of the money of the two users should still be 5000, This is the consistency of transactions .
3、 ... and 、 Isolation, （Isolation）
When multiple users access the database concurrently , For example, when operating the same table , A transaction opened by a database for each user , It cannot be interfered by the operation of other transactions , Multiple concurrent transactions should be isolated from each other , such as A Withdrawing money from a bank card , stay A Before the withdrawal process is over ,B You can't transfer money to this card .
Four 、 persistence （Durability）
Once a transaction is committed , Then all updates to the database will be saved to the database , Cannot be rolled back .