SQL Server 2019 New DMF sys.dm_db_page_info

Microsoft released preview of SQL Server 2019 recently in Ignite 2018. With every release of SQL Server is enriched with new dynamic management view and functions along with enhancements to existing features.

In this article, we will view the newly introduced dynamic management function (DMF) sys.dm_db_page_info and explore the different scenarios around it.

Overview of sys.dm_db_page_info

SQL Server 2019 provides new database management function ‘sys. dm_db_page_info’ to get information about the pages in SQL Server. Prior to SQL Server 2019, we use undocumented dynamic management function sys.dm_db_database_page_allocations and DBCC Page to get details information about the page in SQL Server for the tables, indexes.

Dynamic Management function sys.dm_db_page_info DMF is introduced to replace DBCC Page function but this DMF returns only page header information while DBCC page shows complete details of the page. We will see this later in the demo section.

Before we move further, let us take a look of new dynamic management function (DMF) syntax and parameters.

Syntax for sys.dm_db_page_info

sys.dm_db_page_info ( DatabaseId, FileId, PageId, Mode )

Below are the parameters to pass into sys.dm_db_page_info.

Argument Description Null allowed Allowed Values

DatabaseId

It is unique ID of the database

No

DBID, or we can use DB_ID() for the current database

FileId

It is ID of the database file

No

DB file id

PageId

It is ID of the page we want to examine

No

PageID

Mode

It shows the level of detail in the output of the function

No

LIMITED No information about description columns

DETAILED it gives information about detailed columns as well

We require the VIEW DATABASE STATE permission in the database. We can provide permissions to run with below command.

GRANT VIEW DATABASE STATE TO [login]

To move further, let us create the sample database and data.

Create Database SQL2019 Go Use SQL2019 Go Create table DemoSQL2019 ( ID int identity(1,1), Name varchar(10) ) Go Insert into DemoSQL2019 Values ('SqlShack')

In this article, we will take an overview of new DMF sys.dm_db_page_info along and compare it with the previously used DMF sys.dm_db_database_page_allocations.

Now let us view the information about all the pages and extents allocated for the table using the DMF sys.dm_db_database_page_allocations. This is undocumented DMF introduced in SQL Server 2012.

Syntax for sys.dm_db_database_page_allocations:

sys.dm_db_database_page_allocations

(@DatabaseId , @TableId , @IndexId , @PartionID , @Mode)

Argument Description Null allowed Allowed Values

DatabaseId

It is unique ID of the database.

No

DB ID

TableID

It is ID of the database file.

Yes

Table ID or Null

IndexID

It is ID of the page we want to examine

Yes

Index ID or Null

PartionID

We can pass PatitionID if we require.

Yes

partitionID or Null

Mode

It shows the level of detail in the output of the function

No

LIMITED If we use this parameter, it does not show any information about description columns.

DETAILED it gives information about detailed columns as well.

We cannot provide Null value in this parameter.

Now run the below query to get information about allocated page id and page type description.

Select database_id,DB_name(database_id) as [Database], allocated_page_page_id , page_type_desc from sys.dm_db_database_page_allocations(DB_ID(),null,null,null,'Detailed')

In the above query, we can directly pass the DB ID as well. We can get the DB ID from the sp_helpdb or sys.sysdatabases.

Now we can view the information about any particular page from DBCC Page.

Below is the syntax for DBCC Page:

dbcc page ( {‘dbname’ | dbid}, filenum, pagenum [, printopt={0|1|2|3} ])

Printout values can be as:

0 Prints only page header related information 1 Prints page header and page slot array dump with hex dump for each row 2 Prints page header and whole page hex dump 3 Prints detailed information of per row along with page header

Note: We need to turn on trace flag 3604 for DBCC Page to show output in SQL Server Management Studio.

DBCC TRACEON(3604) DBCC page (6,1,157,3) WITH TABLERESULTS

We can see that DBCC Page gives detailed information about the page.

Now if we view the same thing from the newly introduced sys.dm_db_page_info. We will use the same page id as used before for a comparison purpose.

We can see here that sys.dm_db_page_info gives one row with all the page information for a given parameter in the detailed mode as specified by us.

Note here, we are using the mode as limited so we can see there are some columns showing null values (highlighted by blue arrow)

Select * from sys.dm_db_page_info(6,1,157,’limited’)

Important columns in Sys.dm_db_page_info are:

Column Description

database_id

Database ID

page_type_desc

Page type description such as data page, index page, IAM page

page_level

It shows the Level of the page in the index. For a leaf level, its value is 0

slot_count

It shows the total slot counts. It is number of rows for a data page,

ghost_rec_count

A number of ghost records that are marked for deletion.

is_iam_pg

If that particular page is IAM page, its value