I am sharing one of the very common and important Interview Questions separately so that SQL Server DBAs can recognize very easily before going for SQL DBA Interview.

The question itself is one kind of common problem which is facing by many of SQL DBAs. When SQL Server transaction log full, they are getting an error like “SQL Server Error 9002 transaction log full”.

When an interviewer asks this question to you, you should give a very clear answer with a just list of few options. If they ask more, only you should explain in details; otherwise, it is OK.

Your answer should be like this,
If we got error 9002 transaction log full, we should take following points:

• We should take backup the transaction log file and truncate the transaction log
• We can move log file to another disk drive
• We can increase the size of log file
• We can also add a new transaction log file in separate disk

I am not sharing more details on each point. If you want, you should prepare it for yourself, but I would suggest avoiding detail answer because you need to prepare different commands for all the options.

Here, I am sharing one of the important topics for the internal Storage File Architecture of the SQL Server.

SQL Server is managing two different kinds of files one is for Data and other is for Log information.
The File-groups is a collection of database files, and it helps to manage database files.

Type of the SQL Server Database Files.

Primary Data File (.mdf):

The Primary Data File is starting point of the database and also points to the other files.

Each database has only one primary data file, and it stores all the tables, indexes, views, functions, and other database objects.

It also contains information about the location of all other files.
The default extension of this data file is .mdf.

Secondary Data File (.ndf):

When database exceeds the maximum allocated size, Secondary Data File helps the database to continue to grow. The extension of this file is .ndf.
This is not mandatory to create this file for each database.

When we are configuring table partitions, we can create separately .ndf file to store partition data.

Log File (.ldf):

This file contains all transaction log information of a database which helps us to recover an entire database in case of any loss.
The Database Transactions are written to the log file even before they are written to the data file.

All the database file can grow automatically from their specified size and if we have not specified default size, it can continue to grow until the disk full.

The Filegroup is a logical container of the database files, and the Primary Filegroup is a default Filegroup which contains a primary data and log file of a database.
If there are multiple files in a Filegroup, they will not auto-grow until all the files are full.