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Archive for December 14th, 2012

Scripts to monitor SQL Server Memory usage in Buffer Pool, Plan Cache and identify Query Memory grants & waits by session

Posted by Sudarshan Narasimhan on December 14, 2012


I often use a multitude of T-SQL queries and scripts when I am troubleshooting memory issues and even for monitoring SQL Server Memory usage. I am posting these scripts here in the spirit of sharing, as I’m sure there are other variations of these same scripts out there already. For this purpose of this blog post, these scripts are only useful in troubleshooting out-of-memory (OOM) and other issues in the Buffer Pool. This blog post does not cover Virtual Address/Virtual Memory or memory tracking outside of the Buffer Pool. That will be covered in a later post.

In case you have other scripts for memory monitoring, please leave behind a comment


– Query to find the Buffer Pool usage per each Database
– Each of these pages are present in the Buffer Cache, meaning they are IN_RAM pages.

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 BufCount 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
  
[Database_Name] = CASE [database_id] WHEN 32767
       THEN
‘MSSQL System Resource DB’
      
ELSE DB_NAME([database_id]) END
,
  
[Database_ID]
,
  
db_buffer_pages as [Buffer Count (8KB Pages)]
,
  
[Buffer Size (MB)] = db_buffer_pages / 128
,
  
[Buffer Size (%)] = CONVERT(DECIMAL(6,3
),
      
db_buffer_pages * 100.0 / @total_buffer
)
FROM BufCount
ORDER BY [Buffer Size (MB)] DESC
;

Output

image


-- Query to identify objects that are taking up most of that memory in Buffer Pool.
-- This is only for the current database context. Please prefix <USE DBNAME> as per your requirement

SELECT TOP 25 
 DB_NAME(bd.database_id) as DBNAME,
 obj.[name] as [Object Name],
 sysobj.type_desc as [Object Type],
 i.[name]   as [Index Name],
 i.[type_desc] as [Index Type],
 count(*)AS Buffered_Page_Count ,
 count(*) * 8192 / (1024 * 1024) as Buffer_MB,
 bd.page_type as [Page Type] -- ,obj.name ,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_id
LEFT JOIN sys.indexes i on i.object_id = obj.object_id AND i.index_id = obj.index_id
LEFT JOIN sys.objects sysobj on i.object_id = sysobj.object_id
WHERE database_id = DB_ID()
and sysobj.type not in ('S','IT')
GROUP BY DB_NAME(bd.database_id), obj.name, obj.index_id , i.[name],i.[type_desc],bd.page_type,sysobj.type_desc
ORDER BY Buffered_Page_Count DESC


Output

image


-- Query to show current memory requests, grants and execution plan for each active session
-- This shows memory granted & requested for currently active sessions on the instance level
-- This can be used in a script to capture information over a period of time.

SELECT mg.session_id, mg.requested_memory_kb, mg.granted_memory_kb, mg.used_memory_kb, t.text, qp.query_plan 
FROM sys.dm_exec_query_memory_grants AS mg
CROSS APPLY sys.dm_exec_sql_text(mg.sql_handle) AS t
CROSS APPLY sys.dm_exec_query_plan(mg.plan_handle) AS qp
ORDER BY 1 DESC OPTION (MAXDOP 1)

Output

image

Note: When you click on the query_plan, it opens up the XML Showplan in SSMS.


-- Query to search plan cache for queries with memory grants completed

SELECT top 50 t.text, cp.objtype ,qp.query_plan, cp.usecounts, cp.size_in_bytes as [Bytes Used in Cache]
FROM sys.dm_exec_cached_plans AS cp
JOIN sys.dm_exec_query_stats AS qs ON cp.plan_handle = qs.plan_handle
CROSS APPLY sys.dm_exec_query_plan(cp.plan_handle) AS qp
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS t
WHERE qp.query_plan.exist('declare namespace n="http://schemas.microsoft.com/sqlserver/2004/07/showplan"; //n:MemoryFractions') = 1
order by cp.size_in_bytes desc
OPTION (MAXDOP 1)

Output

image


-- Queries that have requested memory or waiting for memory to be granted
SELECT  DB_NAME(st.dbid) AS [DatabaseName] ,
        mg.requested_memory_kb ,
        mg.ideal_memory_kb ,
        mg.request_time ,
        mg.grant_time ,
        mg.query_cost ,
        mg.dop ,
        st.[text]
FROM    sys.dm_exec_query_memory_grants AS mg
        CROSS APPLY sys.dm_exec_sql_text(plan_handle) AS st
WHERE   mg.request_time < COALESCE(grant_time, '99991231')
ORDER BY mg.requested_memory_kb DESC ;

Note: This query can be used when there are active sessions waiting on memory to be granted and they are waiting. These sessions will have a wait_type of RESOURCE_SEMAPHORE. You can calculate the wait time for memory grant, by subtracting request_time and grant_time


-- SQL Server 2005/2008/R2 version
-- Top clerks ordered by memory used
SELECT TOP(20) [type] as [Memory Clerk Name], SUM(single_pages_kb) AS [SPA Memory (KB)],
SUM(single_pages_kb)/1024 AS [SPA Memory (MB)]
FROM sys.dm_os_memory_clerks
GROUP BY [type]
ORDER BY SUM(single_pages_kb) DESC;
-- SQL Server 2012 version
-- Top clerks ordered by memory used
SELECT TOP(20) [type] as [Memory Clerk Name], SUM(pages_kb) AS [SPA Memory (KB)],
SUM(pages_kb)/1024 AS [SPA Memory (MB)]
FROM sys.dm_os_memory_clerks
GROUP BY [type]
ORDER BY SUM(pages_kb) DESC;

Output

image


That’s all for now folks!

- TheSQLDude (Sudarshan)

Posted in Memory, Performance, T-SQL | Tagged: , , , , , , , , , | 6 Comments »

 
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