MySQL transaction explanation

mysql Storage engine ：

          View engine mode ：SHOW ENGINES;

          Not all storage engines support things in the storage engine ,innodb stay 5.0 Things are supported after version , and myisam and memory It doesn't support things .

 mysql Transaction features ACID：

                Atomicity ：  The business is indivisible , Either all success or all failure , Bundled execution .

                Uniformity ：  The data must be consistent , If you transfer money, add 1000 and subtract 1000 , The total amount is

                                 two thousand ,( The consistent state of one data to the consistent state of another data ) No matter how you operate

                                 The total data will not change .

                Isolation, ：  A transaction cannot be disturbed by other things when it is executed , Other things can be locked if they want to be executed

                persistence ：  Once a transaction is executed, it cannot be modified , Once submitted to the database, the data will be permanently modified .

Transaction creation ： 

        Implicit things ： For example, we usually carry out insert、update、delete. He will help us open implicit things by default .

        Show things ： A transaction has distinct open and end tags . However, the prerequisite is that the auto submit function must be set to disabled

        

 Open process ：
         Auto submit function off 
        set autocommit=0;
         Opening things 
        start transaction;
         To write SQL Add, delete, change and check the sentences ......
         success ：commit; Submit things 
         Failure ：rollback; Things roll back 

    Transaction isolation mechanism ：       

        Dirty reading ： For the query , It means that two transactions perform data operations at the same time , The data read is different .

        It can't be read repeatedly ： It means that the data cannot be read repeatedly after being read once , Avoid inconsistency between two data reads .

        Fantasy reading ： Unreal reading generally refers to adding and deleting , It means that more data is read in the second time after the data is read in the first time

                    One line or less , This is called Unreal reading .

      Transaction isolation level :

                     Dirty reading         It can't be read repeatedly         Fantasy reading 
read uncommitted     √           √               √
read committed       ×           √               √
repeatable read      ×           ×               √
serializable         ×           ×               ×

mysql The default is  repeatable read  Isolation level 
 View the isolation level command ： select @@tx_isolation;
 Set isolation level command ： set session|global transaction isolation level  Isolation level ;