Transaction Isolation

The MS SQL Server supports the parallel execution of queries. Several users can be connected to the server and perform queries at the same time. Therefore, there can be situations where one transaction tries to access the data while another is modifying it. When two transactions tamper with the same set of data, information might become inconsistent or the results of transactions might not be correct. To avoid such cases, the MS SQL Server employs a blocking mechanism called transaction isolation, which consists of several levels.

Potential issues

Before discussing different levels of transaction isolation, let’s look at possible problems that can arise when two transactions are executed simultaneously. The following table provides a good summary.