Database transactions

Business

Basic introduction

• Concept ： If a business operation contains multiple steps , Managed by affairs , So these operations are either successful at the same time , Or fail at the same time
• operation
  （1） Open transaction ：start transaction
  （2） Roll back ：rollback
  （3） Submit ：commit
• Transaction submission method
  （1） Automatic submission
  mysql It's automatic submission
  One DML（ Additions and deletions ） Statement will automatically commit a transaction
  （2） Manual submission
  Oracle The default is manual submission
  You need to start the transaction first , Submit again
  （3） Modify the default submission method
  View the default transaction submission method ：SELECT @@autocommit
  1 Represents automatic submission ,0 Indicates manual submission
  Modify the default submission method ：SET @@autocommit = 0
  In this case, the modification operation is performed when the submission operation is not performed , It's only temporary , Will not affect the actual database

Four characteristics

• Atomicity ： Is the smallest divisible unit , Or at the same time , Or fail at the same time
• persistence ： When a transaction is committed or rolled back , The database will persist the data
• Isolation, ： Multiple transactions are independent of each other
• Uniformity ： Before and after transaction operation , The total amount of data remains the same

The isolation level of the transaction

• Concept ： Multiple transactions are independent of each other , But if multiple transactions operate on the same batch of data , It will cause some problems , Setting different isolation levels can solve these problems
• Existing problems ：
  （1） Dirty reading ： One transaction reads uncommitted data from another transaction
  （2） It can't be read repeatedly （ Virtual reading ）： In the same transaction , The data read twice is not the same
  （3） Fantasy reading ： A transaction operation （DML） All records in the data sheet , Add a piece of data to another transaction , Then the first transaction cannot query its own modification
• Isolation level
  （1）read uncommitted： Read uncommitted
  A problem ： Dirty reading , It can't be read repeatedly , Fantasy reading
  （2）read committed： Read submitted （Oracle Default ）
  A problem ： It can't be read repeatedly , Fantasy reading
  （3）repeatable read： Repeatable （Mysql Default ）
  A problem ： Fantasy reading
  （4）serializable： Serialization
  Can solve all the problems
• Be careful ： Isolation level from small to large , Security is getting higher and higher , But the efficiency is getting lower
• Query isolation level
  select @@tx_isolation
• Set isolation level
  set global transaction isolation level Level string

JDBC Manage affairs

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class JDBCDemo {
    
    public static void main(String[] args) throws SQLException {
    
        Connection conn = null;
        try{
    
            conn = JDBCUtils.getConnect();
            // Open transaction 
            conn.setAutoCommit(false);

            //sql perform 

            // Commit transaction 
            conn.commit();
        } catch (Exception e) {
    
            e.printStackTrace();
            // Something goes wrong , Roll back  
            conn.rollback();
        }finally {
    
            // close resource 

        }
    }
}