To guarantee consistency and recoverability of the information, SQL Server considers every data modification as part of a transaction. It will record transaction information, and every modification made as part of every transaction, in a transaction log. In other words, SQL Server first records how the data will be modified, and then it modifies the data. The logical process could be explained as follows:
A data modification is requested.
SQL Server creates a query plan to execute the data modification request.
SQL Server starts a transaction and records it in the transaction log.
SQL Server writes every operation to apply to the data in the transaction log before modifying the data.
After the operations are registered ...