Four isolation levels for database transactions

There are 4 isolation levels for database transactions, from low to High:

Read UNCOMMITTED	READ UNCOMMITTED read not authorized	Read to allow other Two transactions cannot be written at the same time	Transaction B reads transaction A for the submitted data	Avoid dirty reads when updates are lost
Read committed	Authorize read Read commit	Read to allow other uncommitted transactions to prevent other transactional accesses from being made	Transaction a reads data transaction b changes data transaction A reads B changed data, inconsistent results	Prevent Dirty reads from appearing as non-repeatable reads (duplicate read results are different)
REPEATABLE READ	REPEATABLE READ	Read does not allow write transactions to write prohibit other transactions from being made	Transaction a reads R1 and modifies R2 transaction B cannot modify R1 and read r2,b does not affect a If a contains a statistic that records a range of operations, and B just inserts a record within the range, causing a phantom read	REPEATABLE READ There will be Phantom reads
Serializable	Serialization of	Transactions can only be executed one after another, not concurrently	Highest transaction isolation level, low performance, typically rarely used	Avoid dirty reading , avoid non-repetition reading , avoid phantom reading

Four isolation levels for database transactions