Four characteristics and isolation level of MySQL transactions

-- The ideal state of a transaction at the time of operation ： Keep all transactions isolated , They don't influence each other . Because concurrent operations , Multiple users access the same at the same time data . Problems that may cause concurrent access ：
    -- Dirty reading : One thing reads uncommitted data from another
    -- Fantasy reading ： The amount of data read twice in a transaction is inconsistent , It is required that the number of data read multiple times in a transaction is consistent Of , This is a insert or delete Problems caused by
    -- It can't be read repeatedly ： The data read twice in a thing is inconsistent , The requirement is that the data is consistent when read multiple times in a transaction , this It's a business update Problems caused by
-- The four characteristics of things A（ Atomicity ）C( Consistent line )I( Isolation, )D( persistence )
-- The level of isolation of things
-- read uncommited: Read uncommitted （ The lowest level , The worst security ） Dirty reading will occur 、 It can't be read repeatedly 、 Fantasy reading
-- read commited: Read submitted （ Can prevent dirty reading ）, There will be non repeatable reading 、 Fantasy reading
-- repeatable read: Repeatable （ Prevent dirty reading , Non rereadable questions ）, Can't prevent unreal reading
-- serializable: Serialization （ It can prevent dirty reading 、 Don't reread 、 Fantasy reading ）, efficiency （ Low performance ）    

-- The higher the isolation level of the transaction , The highest security but the lowest performance ！

-- View the isolation level of the transaction
SELECT @@tx_isolation; -- mysql The default isolation level ：repeatable read: Repeatable ！