Transaction Log File Transaction Log File, with the extension ldf, is a very important but often overlooked part of the database structure. It is a file used to record database updates. It can record any operation on the database and save the recorded results to a separate file. For each database update process, the transaction log file has a very comprehensive record. Based on these records, the state before the database update can be restored.
For performance reasons, SQL Server stores user changes in the cache. These changes will be written to the transaction log immediately, but not to the data file immediately. The transaction log uses a mark point to determine whether a transaction has written data from the cache to the data file. When SQL Server restarts, it will check the latest mark point in the log and erase the transaction records after this mark point, because these transaction records do not actually write the data in the cache to the data file. This prevents those interrupted transactions from modifying the data files.
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