JDBC day 6

Isolation level: controls the security of data in the database

Data inconsistency:
Table Student Field age = 20
Thread a thread B
---------------------------------------------------------------------------
Dirty data
20 20
20 + 1 commit
20 + 2 commit

Non-repeated read
20 20
20 + 1 commit
21

Phantom read
Count (*) = 12
Delete ..
Count (*) = 11

Database vendors have made some general solutions to these problems: isolation level
Isolation level:
Transaction_none 0
Transaction_read_uncommitted 1
* Transaction_read_committed dirty data 2
Transaction_repeatable_read dirty data cannot be read repeatedly 4
Transaction_serializable dirty data cannot be read repeatedly. Phantom read 8

From top to bottom, the security is getting higher and the efficiency is getting lower and lower.

Connection. settransactionisolation (INT level)

Metadata: data used to describe data
Table Structure = Description = business data in the table
Dict = Description = data of the database itself

Databasemetadata = dict
Resultsetmetadata = table structure