Search This Blog

Tuesday, February 12, 2008

What all objects are consuming memory (and how much)

To determine what plans are in the cache and how often they're used we can use sys.dm_os_memory_cache_counters dm view .

SELECT TOP 6 LEFT([name], 20) as [name], LEFT([type], 20) as [type], [single_pages_kb] + [multi_pages_kb] AS cache_kb, [entries_count]FROM sys.dm_os_memory_cache_counters order by single_pages_kb + multi_pages_kb DESC

here :
CACHESTORE_OBJCP are compiled plans for stored procedures, functions and triggers. CACHESTORE_SQLCP are cached SQL statements or batches that aren't in stored procedures, functions and triggers. This includes any dynamic SQL or raw SELECT statements sent to the server. CACHESTORE_PHDR These are algebrizer trees for views, constraints and defaults. An algebrizer tree is the parsed SQL text that resolves the table and column names.
(you will find these counters in DBCC Memorystatus as well.Infact DBCC Memory Status uses this dm)

Generally you will find that CACHESTORE_SQLCP > CACHESTORE_OBJCP , but if the ratio of one to another is very high then we can say that there are more adhoc plans being run then Stored procedures.That is the reason the sal statements are going in to Plan cache.
You can also monitor the number of data pages in the plan cache using Performance Monitor (PerfMon) using SQLServer:Plan Cache object with the Cache Pages counter. There are instances for SQL Plans (CACHESTORE_SQLCP), Object Plans (CACHESTORE_OBJCP) and Bound Trees (CACHESTORE_PHDR). This will give you the same picture ..for e.g. under bound tree : multiply cache pages by 8. you will get the same output as in dbcc memorystatus and the dm we used above.

After this we can use sys.dm_exec_cached_plans and sys.dm_exec_sql_text dm views to find the queries :
select TOP 100 objtype, usecounts, p.size_in_bytes/1024 'IN KB', LEFT([sql].[text], 100) as [text]from sys.dm_exec_cached_plans pouter apply sys.dm_exec_sql_text (p.plan_handle) sqlORDER BY usecounts DESC

And then we can check the query plans(and size) for the one we have some doubt .

Now , SQL Server memory is primarily used to store data (buffer) and query plans (cache). We will try to find what tables and indexes are in the buffer memory of your server you can use sys.dm_os_buffer_descriptors DMV.Further , the query below can give us total currrent size of buffer pool .

select count(*) AS Buffered_Page_Count ,count(*) * 8192 / (1024 * 1024) as Buffer_Pool_MBfrom sys.dm_os_buffer_descriptors

After we have found the Bufferpool size , we can see which database is using more memory by runnig the query below :

SELECT LEFT(CASE database_id WHEN 32767 THEN 'ResourceDb' ELSE db_name(database_id) END, 20) AS Database_Name, count(*)AS Buffered_Page_Count, count(*) * 8192 / (1024 * 1024) as Buffer_Pool_MBFROM sys.dm_os_buffer_descriptorsGROUP BY db_name(database_id) ,database_idORDER BY Buffered_Page_Count DESC

And then we can go further at object level to see what all objects are consuming memory (and how much) .We can use the query below in each database we wish to :

SELECT TOP 25 obj.[name], i.[name], i.[type_desc], count(*)AS Buffered_Page_Count , count(*) * 8192 / (1024 * 1024) as Buffer_MB -- , ,obj.index_id, i.[name]FROM sys.dm_os_buffer_descriptors AS bd INNER JOIN ( SELECT object_name(object_id) AS name ,index_id ,allocation_unit_id, object_id FROM sys.allocation_units AS au INNER JOIN sys.partitions AS p ON au.container_id = p.hobt_id AND (au.type = 1 OR au.type = 3) UNION ALL SELECT object_name(object_id) AS name ,index_id, allocation_unit_id, object_id FROM sys.allocation_units AS au INNER JOIN sys.partitions AS p ON au.container_id = p.hobt_id AND au.type = 2 ) AS obj ON bd.allocation_unit_id = obj.allocation_unit_idLEFT JOIN sys.indexes i on i.object_id = obj.object_id AND i.index_id = obj.index_idWHERE database_id = db_id()GROUP BY, obj.index_id , i.[name],i.[type_desc]ORDER BY Buffered_Page_Count DESC


Anonymous said...

Hello guys, I would like to know if there are this Script to SQL 2005 version. Thank You.
Best Regards

Abhay said...

It works in 2005 and above only ...
Best Regards