John Sansom - SQL Server DBA in the UK » Dynamic Management Views (DMV)

How much memory is each SQL Server database using?

John Sansom — Fri, 25 Jun 2010 09:11:52 +0000

Whilst perusing the forums over at SQL Server Central today I stumbled across an interesting question regarding how to identify how much memory is being used by SQL Server on a per database level.

As you know SQL Server stores database data and index pages in memory in an area know as the Buffer Pool. Using my trusty friend Google, I researched an answer to this question on ServerFault provided by Paul Randal. The solution made use of the SQL Server Dynamic Management View (DMV) sys.dm_os_buffer_descriptors

As you know I’m a big fan of using SQL Server DMV’s and so I wanted to take note of this handy SQL code snippet here in order to share it with you.

SELECT
(CASE WHEN ([is_modified] = 1) THEN 'Dirty' ELSE 'Clean' END) AS 'Page State',
(CASE WHEN ([database_id] = 32767) THEN 'Resource Database' ELSE DB_NAME (database_id) END) AS 'Database Name',
COUNT (*) AS 'Page Count'
FROM sys.dm_os_buffer_descriptors
GROUP BY [database_id], [is_modified]
ORDER BY [database_id], [is_modified];
GO

You may also find interesting…….

SQL Snippet: SQL Server Wait Types

John Sansom — Tue, 29 Dec 2009 15:52:21 +0000

Here is a handy little SQL Snippet that will return information about those all important SQL Server Wait Types for your server. It uses the SQL Server Dynamic Management View (DMV) sys.dm_os_wait_stats in order to extrapolate the desired information. A column has also been added to provide details of the percentage of total wait time that a particular Wait Type is responsible for.

T-SQL Query to rank SQL Server Wait Types by highest percentage of total wait time

SELECT
wait_type,
waiting_tasks_count,
max_wait_time_ms,
resource_wait_time_ms = (wait_time_ms - signal_wait_time_ms),
PercentOfAllResourceWaitTime =
(cast((wait_time_ms - signal_wait_time_ms) AS decimal(19,2)) /
(SELECT sum((wait_time_ms - signal_wait_time_ms)) FROM sys.dm_os_wait_stats))
* 100
FROM sys.dm_os_wait_stats
ORDER BY PercentOfAllResourceWaitTime DESC

I hope you find this SQL Snippet useful in your administration of SQL Server. If you have any queries regarding this snippet, SQL Server Wait Types or anything to do with SQL Server whatsoever then be sure to let me know!

DMV Query to identify all active SQL Server Sessions

John Sansom — Wed, 03 Jun 2009 00:24:09 +0000

You may already be aware that I am a big advocate of the SQL Server Dynamic Management Views (DMV’s) and the benifits that they bring to the Database Administrator. They certainly came in handy with a requirement I had recently whereby I needed to identify the IP Address of a specific SQL Server Login and so I would like to share my solution with you.

The query below identifies all currently active SQL Server user connections by their SQL Server Login name. It provides details of the IP address that the connection is sourced from, along with the number of sessions and connections that the SQL Server Login is currently responsible for.

SELECT
    B.login_name,
    A.client_net_address,
    NoOfConnections = COUNT(*)
FROM
    sys.dm_exec_connections A
		INNER JOIN sys.dm_exec_sessions B ON
			A.session_id = B.session_id
GROUP BY
    login_name,
    client_net_address

This is achieved by using two of SQL Server DMV’s:

How to identify the most costly SQL Server queries using DMV’s

John Sansom — Fri, 15 May 2009 12:04:00 +0000

I was investigating a performance issue recently and so thought I would share the T-SQL query that I created with you.

There’s nothing new or magic here, the code snippet simply identifies the top 20 most expensive queries (currently cached) based on the cumulative CPU cost.

The query returns both the SQL Text from the sys.dm_exec_sql_text DMV and the XML Showplan data from the sys.dm_exec_query_plan DMV.

T-SQL to identify the Top 20 most costly queries in terms of Total CPU

SELECT TOP 20
qs.sql_handle,
qs.execution_count,
qs.total_worker_time AS Total_CPU,
total_CPU_inSeconds = --Converted from microseconds
qs.total_worker_time/1000000,
average_CPU_inSeconds = --Converted from microseconds
(qs.total_worker_time/1000000) / qs.execution_count,
qs.total_elapsed_time,
total_elapsed_time_inSeconds = --Converted from microseconds
qs.total_elapsed_time/1000000,
st.text,
qp.query_plan
FROM
sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS st
CROSS apply sys.dm_exec_query_plan (qs.plan_handle) AS qp
ORDER BY qs.total_worker_time DESC

Dynamic Management Views (DMV’s) Used

sys.dm_exec_query_stats
- Returns performance statistics for cached query plans. This contains one row per query plan so if a stored procedure or batch contains two SELECT statements you may get two rows here

sys.dm_exec_sql_text
- Returns the text of the sql statement based on the SQL handle

sys.dm_exec_query_plan
- Returns the showplan in XML format for a batch or module based on the plan handle

Reviewing the results

If you want to investigate a specific query plan further, you may view the graphical execution plan of a particular query by completing the following steps.

Click the hyperlink in the query_plan column for the appropriate row. This will open the XMLShowplan data into a new tab within SQL Server Management Studio.
Save the document by using the Save As option.
Choose the “All File(*.*) fily type option and type .sqlplan as the file extension.
Close the XML document.
Open the file with the .sqlplan extension.

For more comprehensive instruction, see the reference below “How to: Save an Execution Plan in XML Format”.