Four characteristics of transactions

Four characteristics of transactions

•   What is business
•   What is a database transaction
•   What is business ACID Characteristics

What is business

A transaction is a logical set of operations , Or both , Either not .
Classic case
The most classic and often cited example of a transaction is a transfer . If Xiaoming wants to transfer money to Xiaohong 1000 element , There are two key operations involved in this transfer ：

1. Reduce Xiao Ming's balance 1000 element
2. Increase the balance of Xiaohong 1000 element .

The transaction takes these two operations as a logical whole , This whole contains operations that either succeed , Or they all have to fail . In this way, the balance of Xiaoming will not decrease while that of Xiaohong will not increase .

What is a database transaction

Database transactions are the most frequently encountered in our daily development . If your project belongs to a single architecture , You are often exposed to database transactions .
At ordinary times , When we're talking about business , If it doesn't refer to Distributed transactions , It often refers to Database transactions .
What's the use of database transactions ？
Simply speaking ： Database transactions can guarantee multiple operations on the database （ That is to say SQL sentence ） Form a logical whole . The database operations that make up this logical whole follow ： Or it all works , Or none at all .

Log in and copy

#  Start a transaction  START TRANSACTION; 
#  multiple  SQL  sentence  SQL1,SQL2... 
#  Commit transaction  COMMIT;

     

      
1.
      
2.
      
3.
     

in addition , Relational database （ for example ：MySQL、SQL Server、Oracle etc. ） Everything has ACID characteristic ：

What is business ACID Characteristics

1. Atomicity （Atomicity） ： Transactions are the smallest unit of execution , Division is not allowed . The atomicity of the transaction ensures that the action is either complete , Or it doesn't work at all ;
2. Uniformity （Consistency）： Before and after the execution of the transaction , Data consistency , For example, in the transfer business , Whether the transaction is successful or not , The total amount of the transferor and payee should be the same ;
3. Isolation, （Isolation）： When accessing the database concurrently , One user's transaction is not interfered by other transactions , The database between concurrent transactions is independent ;
4. persistence （Durabilily）： After a transaction is committed . Its changes to the data in the database are persistent , Even if the database fails, it should not have any impact .

The implementation principle of data transaction ？
We are here to MySQL Of InnoDB Let's take the engine as an example .
MySQL InnoDB Engine USES redo log( Redo log ) Guarantee the business persistence , Use undo log( Rollback log ) To ensure that the business is Atomicity .
MySQL InnoDB The engine goes through Locking mechanism 、MVCC And other means to ensure the isolation of transactions （ The default isolation level supported is REPEATABLE-READ ）.
Ensure the persistence of the transaction 、 Atomicity 、 After isolation , Consistency is guaranteed .

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