LDF is an extension for SQL Server database log files.
The LDF file contains all log information that records database operations, such as the opening and committing of transactions, the creation and modification of database objects, and so on. When data is changed in the database, these operations will be written into the LDF file to ensure data consistency and integrity, and also facilitate data recovery and log rollback operations.
The size of the LDF file depends on the number of active transactions in the database and how often they are written to the log. To maintain high performance, LDF files can be periodically emptied or compressed. Normally, LDF files should be kept in a separate location from the main data file (MDF), and should be backed up to ensure data reliability.
2. LSN time mapping
LSN (Log Sequence Number) time mapping is one of the mechanisms used to manage transaction logs in SQL Server.
It associates LSNs (numeric identifiers) with their corresponding timestamps so that events occurring in the transaction log can be more easily understood and reported. This mapping is done automatically by SQL Server and can be retrieved from the msdb.dbo.backupset and msdb.dbo.restorehistory system tables using the SELECT command.
LSN time mapping can help administrators better understand the changes that occur in the transaction log and the failure recovery process, as well as better plan backup and restore operations.