Isolation level of MySQL, possible problems (dirty reading, unrepeatable reading, phantom reading) and their solutions

Sum up MySQL Isolation level 、 Possible problems and solutions .

Isolation level	Concept	Realization way	What happened	The phenomenon	Illustrate with examples	resolvent
Read uncommitted	When a transaction has not yet been committed , The changes it makes can be seen by other things	Directly return the latest value	Dirty reading	Read data that other transactions have not been committed or rolled back	A Transaction read B Uncommitted data	The isolation level is set to read committed
Read submitted	After a transaction is committed , The changes it makes will be seen by other things	SQL Create a view when the statement executes	It can't be read repeatedly	The data read in a transaction is different （ During this period, other affairs were submitted ）	A The transaction uses the same query statement twice , The result is different .	The isolation level is set to repeatable
Repeatable （ Default ）	Data seen during the execution of a transaction , It is always consistent with the data seen when the transaction is started . Of course, at the level of repeatable read isolation , Uncommitted changes are also invisible to other transactions .	Create a view when the transaction starts , Use this view throughout the transaction .	Fantasy reading	A transaction is retrieved under the same conditions , Found new data （ Can't find the modified data ）	A Transactions put a field in the table +1, It happens to be this time of business B A piece of data is inserted into the table .A After submitting the transaction, the user finds that there is still data that has not been modified , It's like a hallucination .	The isolation level is set to serialization （ Poor efficiency ）, Don't suggest .｜｜ Add range lock RangeS, Lock search scope to read only
Serialization	As the name suggests, for the same line of records ,“ Write ” Will add “ Write lock ”,“ read ” Will add “ Read the lock ”. When there is a read/write lock conflict , Subsequent transactions must wait for the previous transaction to complete , In order to proceed .	Lock

Problems with high isolation levels can occur at low isolation levels , For the sake of brevity, it is not reflected in the table

Some small concepts ：

1. The isolation level is also to complete ACID Medium I（Isolation）, Isolated type
2. MVCC（ Multi version concurrency control ） Help complete the implementation of isolation
3. MySQL Native MyISAM The engine does not support transactions , By InnoDB replace

Partial reference MySQL45 speak