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Determine SQL Server memory use by database and object

MSSQLTips author Aaron Bertrand By:   |   Read Comments (16)   |   Related Tips: More > Dynamic Management Views and Functions
Problem

For many people, the way that SQL Server uses memory can be a bit of an enigma. A large percentage of the memory your SQL Server instance utilizes is consumed by buffer pool (essentially, data). Without a lot of digging, it can be hard to tell which of your databases consume the most buffer pool memory, and even more so, which objects within those databases. This information can be quite useful, for example, if you are considering an application change to split your database across multiple servers, or trying to identify databases that are candidates for consolidation.

Solution

A Dynamic Management View (DMV) introduced in SQL Server 2005, called sys.dm_os_buffer_descriptors, contains a row for every page that has been cached in the buffer pool. Using this DMV, you can quickly determine which database(s) are utilizing the majority of your buffer pool memory. Once you have identified the databases that are occupying much of the buffer pool, you can drill into them individually. In the following query, I first find out exactly how big the buffer pool currently is (from the DMV sys.dm_os_performance_counters), allowing me to calculate the percentage of the buffer pool being used by each database:

-- Note: querying sys.dm_os_buffer_descriptors
-- requires the VIEW_SERVER_STATE permission.

DECLARE @total_buffer INT;

SELECT @total_buffer = cntr_value
  
FROM sys.dm_os_performance_counters
  
WHERE RTRIM([object_name]) LIKE '%Buffer Manager'
  
AND counter_name = 'Total Pages';

;
WITH src AS
(
  
SELECT
      
database_id, db_buffer_pages = COUNT_BIG(*)
      
FROM sys.dm_os_buffer_descriptors
      
--WHERE database_id BETWEEN 5 AND 32766
      
GROUP BY database_id
)
SELECT
  
[db_name] = CASE [database_id] WHEN 32767
      
THEN 'Resource DB'
      
ELSE DB_NAME([database_id]) END,
  
db_buffer_pages,
  
db_buffer_MB = db_buffer_pages / 128,
  
db_buffer_percent = CONVERT(DECIMAL(6,3),
      
db_buffer_pages * 100.0 / @total_buffer)
FROM src
ORDER BY db_buffer_MB DESC;

In the above query, I've included the system databases, but you can exclude them by uncommenting the WHERE clause within the CTE. Note that the actual filter may need to change with future versions of SQL Server; for example, in SQL Server 2012, there is a new database for Integration Services called SSISDB. You may want to keep an eye on system databases just to have a complete picture, seeing as there isn't much you can do about their buffer pool usage anyway - unless you are using master or msdb for your own custom objects.

That all said, here are partial results from an instance on my local virtual machine:

using dmv in sql server 2005 to determine which database is utilizing the majority of your buffer pool memory

Clearly, the SQLSentry database - while only representing 258 MB - occupies about 70% of my buffer pool for this instance. So now I know that I can drill into that database specifically if I want to track down the objects that are taking up most of that memory. You can once again use the sys.dm_os_buffer_descriptors only this time, instead of aggregating the page counts at the database level, we can utilize a set of catalog views to determine the number of pages (and therefore amount of memory) dedicated to each object.

USE SQLSentry;
GO

;WITH src AS
(
  
SELECT
      
[Object] = o.name,
      
[Type] = o.type_desc,
      
[Index] = COALESCE(i.name, ''),
      
[Index_Type] = i.type_desc,
      
p.[object_id],
      
p.index_id,
      
au.allocation_unit_id
  
FROM
      
sys.partitions AS p
  
INNER JOIN
      
sys.allocation_units AS au
      
ON p.hobt_id = au.container_id
  
INNER JOIN
      
sys.objects AS o
      
ON p.[object_id] = o.[object_id]
  
INNER JOIN
      
sys.indexes AS i
      
ON o.[object_id] = i.[object_id]
      
AND p.index_id = i.index_id
  
WHERE
      
au.[type] IN (1,2,3)
       AND
o.is_ms_shipped = 0
)
SELECT
  
src.[Object],
  
src.[Type],
  
src.[Index],
  
src.Index_Type,
  
buffer_pages = COUNT_BIG(b.page_id),
  
buffer_mb = COUNT_BIG(b.page_id) / 128
FROM
  
src
INNER JOIN
  
sys.dm_os_buffer_descriptors AS b
  
ON src.allocation_unit_id = b.allocation_unit_id
WHERE
  
b.database_id = DB_ID()
GROUP BY
  
src.[Object],
  
src.[Type],
  
src.[Index],
  
src.Index_Type
ORDER BY
  
buffer_pages DESC;

Here are the results from this database. Notice that I've captured both clustered and non-clustered indexes, for clustered tables and heaps, and for illustrative purposes I have also created an indexed view.

both clustered and non-clustered indexes have been captured

Please keep in mind that the buffer pool is in constant flux, and that this latter query has explicitly filtered out system objects, so the numbers won't always add up nicely. Still, this should give you a fairly good idea of which objects are using your buffer pool the most.

When investigating the performance of your servers, buffer pool data is only a part of the picture, but it's one that is often overlooked. Including this data will help you to make better and more informed decisions about direction and scale.


Next Steps


Last Update: 5/19/2011


About the author
MSSQLTips author Aaron Bertrand
Aaron Bertrand is a Senior Consultant at SQL Sentry, Inc., and has been contributing to the community for over a decade, first earning the Microsoft MVP award in 1997.

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Comments and Feedback:
Thursday, May 19, 2011 - 4:31:22 AM - Moinu Read The Tip

This is a great article. Is there any way by which we could find out the details of memory used in other places like in proc cache etc?


Thursday, May 19, 2011 - 7:21:41 AM - Ahmad Read The Tip

Goodish !!!

 

somewhat related to buffers i am in need to effectively use DBCC FREESYSTEMCACHE if possible to replace hectic DBCC DropCleanBuffers for during testing performance of queries??

:(

 

 


Thursday, May 19, 2011 - 11:42:16 AM - Aaron Bertrand Read The Tip

Moinu, have a look at these articles from Kimberly Tripp:

http://www.sqlskills.com/BLOGS/KIMBERLY/post/Procedure-cache-and-optimizing-for-adhoc-workloads.aspx

http://www.sqlskills.com/BLOGS/KIMBERLY/post/Plan-cache-adhoc-workloads-and-clearing-the-single-use-plan-cache-bloat.aspx


Sunday, May 22, 2011 - 6:20:30 PM - Daniel Read The Tip

Excellent article!!! Congrats!!!


Wednesday, June 01, 2011 - 4:42:13 PM - TheSmilingDBA Read The Tip

Excellecent article!!!

Need to explain how to use resutls to tune queries or request more RAM.

Thanks,

Thomas


Friday, June 03, 2011 - 12:34:18 PM - Bruce Samuelson Read The Tip

Here's a slight correction to these excellent tools. The last line of the first query should be ordered by buffer pages rather than buffer MB because the latter rounds to the same value for some DBs.

ORDER

 

BY db_buffer_pages DESC, db_name ASC; --db_buffer_MB DESC;


Thursday, June 30, 2011 - 4:05:49 AM - Muratos Read The Tip

Excellent.

Can you develop it further to include sum(row_counts) and sum(real_table_row_count)? I think we can understand whether all table rows in memory or not using that way.


Thursday, May 24, 2012 - 11:57:50 PM - Momfei Read The Tip

GODLIKE!

Excellent article!

Thanks you so much to share this VERY x999 useful technique.


Tuesday, November 20, 2012 - 11:15:22 AM - Krishna Read The Tip

 

Very good article for beginner DBA's.. Thanks alot Sir


Monday, January 21, 2013 - 12:00:24 PM - Ammad Read The Tip

Fantastic article!

Is there a way to include which user or process was accessing the tables?


Monday, January 21, 2013 - 2:08:38 PM - Aaron Bertrand Read The Tip

Ammad not really an easy way through the DMVs directly unless you parse the plan cache for any currently running queries and determine it that way - however that may actually cause more performance problems than you could possibly hope to solve.

If you want to know who is querying specific tables, that might be a better job for trace, audit, or 3rd party monitoring like SQL Sentry Performance Advisor.

http://www.sqlsentry.net/performance-advisor/sql-server-performance.asp

*Disclaimer: I work for SQL Sentry.


Thursday, January 24, 2013 - 8:40:07 AM - John Henderson Read The Tip

It appears that for SQL 2012 in order to get the total buffer value you need to alter the where clause to be "counter_name = 'Database pages';" instead of "counter_name = 'Total Pages';"

Great article though...


Thursday, January 24, 2013 - 10:03:32 AM - Aaron Bertrand Read The Tip

Thanks for the note John; this was written well before SQL Server 2012 was public. :-)


Tuesday, March 19, 2013 - 10:14:39 AM - Kevin Di Sotto Read The Tip

Hi Aaron

Love this query ! Why would indexes that are not being used as much as other indexes  be take up a bigger percentage of buffer memory? Does it all depend on the size of the Index?    

 

 


Tuesday, March 19, 2013 - 4:56:33 PM - Aaron Bertrand Read The Tip

Kevin,

Yes, an index (or a range) is either in memory or not, if it is referenced 15 times or 20 times it is still only represented once.


Tuesday, September 17, 2013 - 8:50:10 AM - Anandan Kanagarajan Read The Tip

Great Post indeed and I used this several time to identify the Databasewise Memory usage on a SQL Server Instance.

While recently using this DatatabaseWise Memory usage query, on the result window, the tempdb is consuming around 2+ Gigs of Memory.

I also used the object wise memory usage query to identify the memory usage of Tempdb. But from the result set I am not getting the details of the entire 2 Gigs of Memory usage that was shown on the result of Databasewise Memory usage.

May I request to shed some light about the Tempdb Memory usage on SQL Server 2008 and how to remove the memory usage with out restarting the instance ?

Thanks in advance



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