MDF and LDF in SQL Server

BRIEF INSTRUCTION ABOUT MDF,LDF
By :
MD MASUM REZA

AGENDA OF THE DAY
 Introduction
 What is MDF , LDF and NDF
 Locating .mdf File .ldf file in server
 Role of MDF and LDF
 Restore data after truncating the
table(with example)
 Differential Backup
 Full Backup
 Conclusion

Introduction :-
The SQL Server provides the facility to restore your database
by attaching your .mdf file and .ldf file to the database.
We can directly Attach our existing .mdf and .ldf file to an SQL
instance by using SQL Server Management Studio or T-SQL.
We can restore our .mdf and .ldf file through execute some query.

What is MDF , LDF and NDF : -
MDF :–Stands for Master Database File. It contains all the main information of the
database that are part of the server. This extension also points to various other files. It
plays a crucial role in information storage. Overall it is very important for safe and secure
supervision of data. In case this file gets damaged, an MDF recovery procedure is
conducted to recover it. Doing so is important in order to save the data from going
missing.
NDF :-stand for Next Data File . NDF file is a user defined secondary database file of
Microsoft SQL Server with an extension .ndf, which store user data. Moreover, when
the size of the database file growing automatically from its specified size, you can use
.ndf file for extra storage and the .ndf file could be stored on a separate disk drive.
Every NDF file uses the same filename as its corresponding MDF file. We cannot open
an .ndf file in SQL Server Without attaching its associated .mdf file.
LDF :–Stand for LOG Database File .This file stores information related to transaction logs
for main data file. It basically keeps track of what all changes have been made in the
database. The information that this file stores ranges from date/time of change, details
of the changes made, as well as information related to whoever made the changes.
Information related to computer terminals where changes took place is also stored in the
logs.

Locating .mdf File .ldf file in server :-
Within each database, you will find two files namely MDF and LDF.
These two are basically file extensions used in Microsoft SQL. These files get automatically
created at the time of database creation. They also share the same storage location. The
reason why these files are so important is because they happen to be part of backup and
recovery process. In simpler words, in case something bad happens to the database, these are
the files the administrator will resort to for restoring and recovering the lost/damaged data.
Query can Execute:
 select * from sys.database_files

Role of MDF and LDF :-
 select * from fn_dblog (null , null)

Role of MDF and LDF
The primary purpose of an LDF file is to provide the ACID concept – Atomicity, Consistency,
Isolation, and Durability
Atomicity: if one part of the transaction fails, the entire transaction fails, and the database state is
left unchanged
Consistency: any transaction brings the database from one valid state to another
Isolation: the execution of concurrent transactions brings the database to a state as if the
transactions were executed serially, one by one
Durability: once committed, the transaction remain so, even in the case of errors, power loss, or
crashes
An LDF file stores enough information to replay or undo a change, or recover the database to a
specific point in time. Therefore, due to various auditing or recovery requirements, there is often a
need to open the LDF file and view its contents. But viewing LDF file content is not an easy task

Restore data after truncating the table :-
The below example will show how can retrieve data after truncate or delete if happen :
use master
1 .create database Test
go
USE Test
GO
CREATE TABLE Student
(
StudentID BIGINT IDENTITY PRIMARY KEY,
StudentName VARCHAR(128),
RollNo VARCHAR(10)
)
GO
INSERT INTO Student(StudentName , RollNo)
VALUES
('Reza','101')
,('Hari','102')
,('Sunil','103')
,('Naveen','104')
GO

3. Take Database Backup :
BACKUP DATABASE Test
TO DISK = 'D:BackupNew folderMyTestDB.BAK'
GO
4. Truncate table student
5. select * from Student
2. select * from Student

6. SELECT
[Current LSN],
Operation,
[Transaction ID],
[Begin Time],
[Transaction Name]
FROM
fn_dblog (NULL, NULL) where [Transaction Name] ='TRUNCATE TABLE‘
7. 00000021:0000005d:0001 take LSN (Log Sequence Numbers) from above code.
8. Convert LSN number from HEX to Decimal number. like below code
SELECT CAST (CONVERT (VARBINARY,'0x'+'00000021', 1) AS INT) as FirstPart, --33
CAST (CONVERT (VARBINARY,'0x'+'0000005d', 1) AS INT) as SecondPart, --93
CAST (CONVERT (VARBINARY,'0x'+'0001', 1) AS INT)as ThirdPart --1
GO

9. Add preceding zeros for 93and 1.
 Note : no need for 33
 93=0000000093 (8 zeroes) total should be 10 digits
 1 =00001 (4 zeroes) total should be 5 digits.
 => 33000000009300001
 Now do following steps one by one .
BACKUP LOG Test
TO DISK = 'D:BackupNew folderMyTestDB.TRN'
GO
RESTORE DATABASE MyTestDB_Copy
FROM DISK = 'D:BackupNew folderMyTestDB.bak'
WITH
MOVE 'Test' TO 'D:BackupNew folderMyTestDB.mdf',
MOVE 'Test_log' TO 'D:BackupNew folderMyTestDB_log.ldf',
NORECOVERY
GO

RESTORE LOG MyTestDB_Copy
FROM
DISK = N'D:BackupNew folderMyTestDB.TRN'
WITH
STOPBEFOREMARK = 'LSN:33000000009300001’
10 . use MyTestDB_Copy
select * from Student

Differential Backup:-
A differential backup is created similarly to a full backup, but with one important difference –
the differential backup only contains the data that has changed since the last full backup (the
active portion of the transaction log). Differential backups are cumulative not incremental. This
means that a differential backup contains all changes made since the last full backup, in spite of
the fact that they have already been included in previous differential backups. Differential backups
are created the following way:
How to Make a Differential Backup
To make a differential database backup simply add “WITH DIFFERENTIAL” clause:
BACKUP DATABASE your_database TO DISK = 'diff.bak' WITH DIFFERENTIAL

Full Backup :-
The simplest kind of SQL Server backup is a full database backup. It provides a complete copy of
the database but allows restoring the database only to a point-in-time when the backup was
made.Even if you add the “WITH STOPAT=<time or log sequence number>” option to restore
command you will not get the expected result because this option applies only when you restore
the transaction log. Please see how a periodic full backup works in the picture below:
How to Make a Full Backup
To make a full backup you can use T-SQL command:
BACKUP DATABASE your_database TO DISK = 'full.bak'
Another way to backup a database is to use
SQL Server Management Studio (SSMS):
right click on the database you want to backup, select “Tasks”, then “Back up…”.
Choose “Full” backup type, add a backup destination and click “OK”.

Conclusion
In the above section, we learned how to restore LDF and MDF files to a database. It
is highly recommended that you have to detach the MDF file before attaching a new
one. This is a very helpful method to restore database using MDF and LDF file.
1. https://sqljumble.blogspot.in/2016/11/how-to-recover-data-after-truncate.html
2. https://sqlbak.com/blog/recover-deleted-data-in-sql-server/
3. https://sqlbak.com/academy

MDF and LDF in SQL Server

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