SQL Server lock mechanism (iv) Overview (impact of various transaction isolation levels)

SQL Server lock mechanism (I) Overview (lock type and scope) SQL Server lock mechanism (ii) Overview (Lock compatibility and lockable resources) this article introduces the SQL Server lock mechanism (iii) Overview (lock and transaction isolation level) vi. The impact of various transaction isolation levels on data modification affects users who read or modify the same data at the same time.

SQL server lock mechanism (I) Overview (lock type and scope) SQL SERVER lock mechanism (ii) Overview (Lock compatibility and lockable resources) this article introduces the SQL SERVER lock mechanism (iii) Overview (lock and transaction isolation level) 6. users with different transaction isolation levels that affect data modification may affect reading or modifying the same data at the same time.

SQL server lock mechanism (I)-Overview (lock types and ranges)

SQL SERVER lock mechanism (II)-Overview (Lock compatibility and lockable resources)

This article introduces the locking mechanism of SQL SERVER (iii) -- Overview (lock and transaction isolation level)

Vi. Impact of various transaction isolation levels

Users who modify data will affect other users who read or modify the same data at the same time. That is, these users can access data concurrently. If the data storage system has no concurrency control and the Hong Kong virtual host is used, the user may see the following negative effects:

· Uncommitted dependency (dirty read)

· Inconsistent analysis (not repeated)

· Phantom read

(1) Dirty read:

For example, Zhang is executing a service on an American server:

TbUnRead, delay --- at this time, Li queries the data in the table. The Hong Kong server is rented and the following statement is executed: tbUnRead