------ transaction database

Transaction (transaction), there are four properties: atomicity, consistency, isolation, durability, in which the most important is the consistency of atomicity, isolation, durability guaranteed.

　　Isolation is divided into:

1. Uncommitted Read (RU)
2. Read Committed (RC)
3. Repeatable Read (RR)
4. Serialization (Serializable)

　　Each level will solve different problems, usually: dirty reads, non-repeatable reads and phantom reads

	Dirty read	Non-repeatable read	Magic Reading
RU	√	√	√
RC	×	√	√
RR	×	×	×
Serializble	×	×	×

　　In the MySql, RR level will not lead to phantom read, such as when using the default select, MySQL using MVCC mechanism to ensure that no phantom read

　　Atomicity: a transaction is complete the operation, the steps of the transaction are not subdivided, it is either executed or not executed

　　Consistency: When the transaction is completed, the data must be in a consistent state

　　Isolation: All modifications transaction data is not disturbed by other transaction is independent, it does not rely on or affect other transactions

　　Durability: After the completion of the transaction, changes to the database are permanently stored, the transaction log to maintain durability of transactions