Recently, I shared an interesting article on the move of your table from one filegroup to another file group by moving only clustered index in SQL Server.

SQL Server: Move your Table from one File Group to another File Group

I got one comment, and one of my readers faced error like “Error 5042 The file ‘FileName’ cannot be removed because it is not empty” while deleting an old file group/data file.
In this post, I am sharing a quick fix of the Error 5042.

The solution is to shrink your empty file before deleting an actual. You can use EMPTYFILE option in DBCC SHRINKFILE to remove all junk data of a file.

DBCC SHRINKFILE(File_Name,EMPTYFILE)

After that, you can remove a file from the database using below ALTER command.

ALTER DATABASE Database_Name REMOVE FILE File_Name

If you are finding most top 10 steps for SQL Server Performance tuning, you could get one of the items in the list is “multiple file-groups and various data-files increases the query performance”.This is correct.

You can move your fat table from master or primary data group to another custom file group.
It gives you more performance and very easy to do maintenance.

I am also asking this question to SQL DBA like “how to move a table from one File Group to another File Group?” and most of the times I am getting answers like “Create new file group -> Replicate table schema -> Move data -> Drop old table”.

The above answer is right, but instead of this great exercise, we can move a table to new file group by creating a clustered index only.

Here, You can access full demonstration.
Create a sample table:

CREATE TABLE tbl_Students 
(
	StudID INT IDENTITY(1,1)
	,Name VARCHAR(10)
	,CONSTRAINT pk_tbl_Students_StudID PRIMARY KEY(StudID)
)
GO

Insert few dummies record:

INSERT INTO tbl_Students(Name) VALUES ('Anvesh')
GO 100000

Check the table Information:

EXEC SP_HELP 'tbl_Students'
GO

Alter a database to add new file group:

ALTER DATABASE Database_Name ADD FILEGROUP New_FileGroup
GO

Add new data file (.ndf):

ALTER DATABASE Database_Name  ADD FILE
(
	NAME = 'New_DataFile', 
	FILENAME = 'C:\TempSQLData\New_DataFile.ndf',
	SIZE = 100000KB,
	FILEGROWTH = 65000KB
) TO FILEGROUP New_FileGroup
GO

Create a new CLUSTERED index on table within created new file group:

CREATE UNIQUE CLUSTERED INDEX pk_tbl_Students_StudID ON tbl_Students(StudID)
WITH
(
	DROP_EXISTING = ON
)
ON New_FileGroup
GO

Check the table information:

EXEC SP_HELP 'tbl_Students'
GO

If you need a space of old table, you can shrink your database:

DBCC SHRINKFILE ('Database_Name' , 0)
GO

The Page in a SQL Server is a small storage unit of data and it resides in a Data File.

When we write the first row in a table, it creates an 8KB page to store the data, and it assigns 0 as a starting number and sequentially increase in a data file.

Each data file has a unique file ID number, and each page has a unique page number.
We can store 128 pages per one megabyte.

The 8KB page doesn’t associate with a single row of data.
If row size is small, multiple rows can store into an 8KB data page. If row size is large and 8KB page is not sufficient to store it, it creates multiple pages.

Each table has a separate data page, and it never merges data
from multiple tables. Even if we have small size of the table, it also creates separate pages for each table.

SQL Server uses different types of pages to store various types of data like Index, Data, Text, BLOB.

The different type of pages are:

Data: stores user’s data, but type of text, ntext, nvarchar(max),varchar(max),varbinary(max),xml, and image.

Index: stores index related data.

Text/Image: stores all large object data type like text,varchar(max).

GAM: stores global allocation map information about extents.

Page Free Space: stores information about the free space of the pages.

IAM: stores index allocation map information about the indexes.

BCM: stores bulk changed map information of the extents.

The internal structure of the Page:

A Data Page consists of three main sections which are Page Header, Actual Data and Row offsets.

Each Data Page has 96-byte header to store system information like page number, page type, free space, page owner’s object id.

After the header information, actual data rows are put on the page serially.

There is one-row offset table at the end of the page, and it stores information about each row.

The records within a page are not always stored in continuous logical order, and the free-space on a page is not always maintained in one contiguous block.

If we delete a record, it creates one free hole within the page, and immediately it cannot be used by new INSERT.

It creates fragmentation on a page and when it is necessary, INSERT check the free block and try to insert best match record into that free block.

This all row’s information kept by the Row offset table.
The Database Administrator also has to perform some maintenance task to remove fragmentation from the data pages.