What is the LDF file in SQL Server?

Question

What is the LDF file in SQL Server? what is its purpose?

can I safely delete it? or reduce its size because sometimes it\'s 10x larger than the database file mdf.

Answer 1

LDF holds the transaction log. If you set your backups correctly - it will be small. It it grows - you have a very common problem of setting database recovery mode to FULL and then forgetting to backup the transaction log (LDF file). Let me explain how to fix it.

1. If your business can afford to lose a little data between backups, just set the database recovery mode to SIMPLE, then forget about LDF - it will be small. This is the recommended solution for most of the cases.
2. If you have to be able to restore to the exact point in time - use FULL recovery mode. In this case you have to take regular Transaction Log backups. The simplest way to do it is to use a tool like SqlBackupAndFTP (disclosure - I am a developer). The log file will be truncated at this time and would not grow beyond certain limits.

Some would suggest to use SHRINKFILE to trim you log. Note that this is OK only as an exception. If you do it regularly, it defeats the purpose of FULL recovery model: first you go into trouble of saving every single change in the log, then you just dump it. Set recovery mode to SIMPLE instead.