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Posts Tagged ‘script’

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 BIGINT;
SELECT @total_buffer = cntr_value
FROM sys.
dm_os_performance_counters
WHERE RTRIM([object_name]) LIKE
‘%Buffer Manager’
AND counter_name = ‘Total Pages’
/AND counter_name = ‘Database pages’ — Uncomment this line & comment the above line, if you’re SQL Server version is 2012 or above/

;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(10,2
), 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_BIG(*) AS Buffered_Page_Count ,
 COUNT_BIG(*) * 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)

 

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Posted in Memory, Performance, T-SQL | Tagged: , , , , , , , , , | 13 Comments »

T-SQL Script for SQL Server Statistics Last Updated Time & Percent Rows modified

Posted by Sudarshan Narasimhan on August 4, 2011


I wrote a post on the same topic @ Amit’s Blog. I made some changes to the script to make it easier for DBA’s to read the output. I am re-posting this here for your reference. This can be quite handy if you are managing multiple SQL instances and you have lot of tables or have large databases where you only want to update statistics on some tables based on row modifications (data changes e.g. OLTP). You can always use DBCC SHOW_STATISTICS or SP_AUTOSTATS to find out the same information for a specific table, index or column stats.

select

schemas.name as table_schema,

tbls.name as Object_name,

i.id as Object_id,

i.name as index_name,

i.indid as index_id,

i.rowmodctr as modifiedRows,

(select max(rowcnt) from sysindexes i2 where i.id = i2.id and i2.indid < 2) as rowcnt,

convert(DECIMAL(18,8), convert(DECIMAL(18,8),i.rowmodctr) / convert(DECIMAL(18,8),(select max(rowcnt) from sysindexes i2 where i.id = i2.id and i2.indid < 2))) as ModifiedPercent,

stats_date( i.id, i.indid ) as lastStatsUpdateTime

from sysindexes i

inner join sysobjects tbls on i.id = tbls.id

inner join sysusers schemas on tbls.uid = schemas.uid

inner join information_schema.tables tl

on tbls.name = tl.table_name

and schemas.name = tl.table_schema

and tl.table_type=‘BASE TABLE’

where 0 < i.indid and i.indid < 255

and table_schema <> ‘sys’

and i.rowmodctr <> 0

and i.status not in (8388704,8388672)

and (select max(rowcnt) from sysindexes i2 where i.id = i2.id and i2.indid < 2) > 0

order by modifiedRows desc


Keep in mind that Rowmodctr values displayed in above output are not entirely reliable starting with SQL 2005 onwards. But, you can rely on last updated time to make a decision if the statistics need to be updated. Read here for more info on this.

 

 

You can use this script to generate the UPDATE STATISTICS command for each table in your table. I am using FULL SCAN by default, which you can of course modify to use specific SAMPLE. You have to un-comment the comments lines, to actually perform the update.

 

select identity(int,1,1) as rownum,table_name into table_count from information_schema.tables where table_type=‘base table’

declare @count int,@stmt varchar (255),@maxcount int,@tblname varchar(50)

set @count=1

select @maxcount=count(*) from table_count

while @count < @maxcount+1

begin

      select @tblname=table_name from table_count where rownum=@count

      set @stmt = ‘UPDATE STATISTICS ‘+ ‘[‘ +@tblname+ ‘]’ + ‘ WITH FULLSCAN’

      print @stmt

      –PRINT (‘Updating statistics for table :’+@tblname)

      –EXEC(@stmt)

      –PRINT (‘Finished Updating statistics for table :’+@tblname)

      print

      set @count=@count+1

      set @stmt=

End

drop table table_count


Have fun with your database maintenanceSmile. As always stay tuned for more cool SQL stuff.

Posted in DB Maintenance | Tagged: , , , , , | 4 Comments »