Solution: Transaction log may help you to track this problem. A transition log may be the evidence for such type of issues.
Essential Operation captured
by Transaction: Before an explanation about
the transaction log, we should know what SQL operations are achieved by
the transaction log.
Transaction log captured all the DML operation like
INSERT, UPDATE, DELETE and also some DDL operation like CREATE, TRUNCATE and
DROP,
Why
to read the SQL Server transaction log?
The transaction log contains all the information about the
transaction we performed in our database. If we did some operation by mistake
like delete or we lost some data, and we want to recover lost data, then the transaction log may help you to resolve
this problem.
Way
of reading the SQL Server transaction log.
We can’t read directly to the transaction log because of
security reasons. SQL Server provides us some function to decode it. The function
are fn_dblog() and fn_dump_dblog(). For the security purpose
transaction log stores the information in an encrypted (not human-readable) format
so we could not read it directly.
View SQL Server
transaction log using fn_dblog() function:
The
fn_dblog() is an undocumented function of SQL Server, which is allowed to view
the transaction log records in the active part of the transaction log file for
the current database.
Fn_dblog() the function takes two parameters, start LSN
and end LSN.
Start LSN: Starting log sequence number, or LSN, you can
also, specify null which means it
will return everything from the start of the log.
End LSN: Ending the log sequence number, or LSN, you can specify null which means you want to return everything to end of the transaction
log.
Note: Undocumented
means, if you are using this function in SQL Server, which is against of
production database instances executed on your own risk. I will explain only
fn_dblog() function only in this article.
How to use fn_dblog() function
in SQL Server?
If
I will explain uses of fn_dblog() on the existing database it may create confusion
so I am using a new database from creation step by step.
1-Step: Create database ‘Codefari.’
USE[master]
GO
CREATE DATABASE Codefari
GO
|
2-Step: Create
table ‘Blogs’.
USE [Codefari]
GO
CREATE TABLE Blogs
(
ID INT IDENTITY(1,1) NOT NULL,
TITLE VARCHAR(MAX)
)
|
3-Step: In this step, we will check how much process
has been used by SQL Server to create a database and table.
USE [Codefari]
GO
SELECT COUNT(*) FROM fn_dblog(null,null)
|
You
can see 180 steps taken by SQL Server to complete this process.
4-Step: In this step, you can see what data
available in the log.
USE [Codefari]
GO
SELECT
[Current LSN],
[Operation],
[Transaction Name],
[Context],
[Transaction ID],
[AllocUnitName],
[Page ID],
[SPID],
[Parent Transaction ID],
[Description]
FROM fn_dblog(NULL, NULL)
|
5-Step: In this step, we will perform some
DML operation and will track transaction information in Log.
INSERT INTO Codefari.[dbo].[Blogs] VALUES('Transaction log in
Codefari')
GO
UPDATE Codefari.[dbo].[Blogs] SET [TITLE]='Transaction log in
Codefari.com' WHERE ID=1
GO
DELETE FROM Codefari.[dbo].[Blogs] WHERE ID=1
GO
|
6-Step: This step will show the transaction which we have performed in 5-step.
USE [Codefari]
GO
SELECT
[Current LSN],
[Transaction ID],
[Operation],
[Transaction Name],
[Context],
[AllocUnitName],
[Page ID],
[Slot ID],
[Begin Time],
[End Time],
[Number of Locks],
[Lock Information]
FROM sys.fn_dblog(NULL,NULL)
WHERE Operation IN
('LOP_INSERT_ROWS','LOP_MODIFY_ROW',
'LOP_DELETE_ROWS','LOP_BEGIN_XACT','LOP_COMMIT_XACT')
|
We
can see in above steps how fn_dblog() function shows the captured transaction
logs and made the transactions in a human-readable format.
Above
Experiment and points give consequences as fn_dblog() can be used when users
want to view the SQL transaction log. Users can easily check the transaction log to
see the activities like page splits or objects being drops etc.
