4 properties database of things.
A atomicity: multiple operations either all succeed, or all fail. undo undo log is the database when the transaction fails to ensure the atomicity of transactions (Atomicity)
C Consistency: consistency of the most difficult to understand. AID characteristics of the database allows the database to achieve consistency, this goal.
I Isolation: two things operate on the same table, it can be done independently of each other. - "Database isolation level -" database isolation level is achieved through the lock - "shared lock (read lock), exclusive lock (write lock)
D persistence: as long as submitted to the end, the data must successfully saved. redu log to repeat a process of data when the power brush / database crash like situation occurs, the brush redo log data to the database to ensure the durability of transactions (Durability Rev)
1, Uncommitted Read (read-uncommitted): In this isolation level, the update will solve the problem of lost, appear dirty reads, non-repeatable read and phantom problem reading.
2. Read Committed (read-committed): there will be problems non-repeatable read and phantom read this isolation level. (This is the default isolation level Oracle)
3, repeatable read (repeatable read): Magic will have problems reading of this case. (This is the default isolation level mysql, mysql In fact, this isolation level to solve the problem of phantom read)
4, serialization (serializable): This isolation highest level, but also the slowest, it is serialized the modalities of implementation. Solve all concurrency problems.
The reason for isolation is complicated by the fault , two things will occur simultaneously concurrent https://blog.csdn.net/apologizetm/article/details/88389785