MS SQL database includes MDF file and LDF file. 

MDF is actual data of an application and LDF file is a transaction log file which records the queries and the result. It can be optimized through "Shrink option for the file.

<How To Check Size of LDF and Reduce the size of the file>

1. Run SQL Management studio as administrator
2. Copy the below query and click on [Execute]
sp_helpdb BioStar;

3. Confirm the size of BioStar_log

4. Stop BioStar Server

5. Mouse right click on BioStar DB name and go Tasks>Shrink>Files

6. Click File Type>Log and click on [OK]

7. Copy the below query and click on [Execute] and check the result.
sp_helpdb BioStar;