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Posted Tuesday, May 27, 2008 10:29 AM
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I have some doubt regarding memory management.

I have sql2005 on windows server 2003 ,64-bit
suppose if have 32 gb of ram, by default how much memory it will take.

As far i concerned by default os will take 2 gb of ram and remaining will be taken by the sql server as per demand.(but i think it will take not more than 2 gb)
could any one tell me that sql serrver memory management is dynamic or not.what exactly happens

Plz give some idea regarding memory management.
Post #507076
Posted Tuesday, May 27, 2008 10:51 AM


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SQL and os will take the Memory as they needed. If you want to strict for SQL and OS, you may need to enable the AWE on SQL server side.

Manoj

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Posted Tuesday, May 27, 2008 12:05 PM
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You are on 64 bit, so don't worry about AWE.

By default, SQL server will dynamically allocate memory. This is configurable to a window of dynamic memory (set a min and max) or you can set it to allocate a specific amount of memory.

SQL 2000 did not do an efficient job of dynamically allocating memory, but SQL 2005 does it rather well (MS made big improvements here).

Every system is different. It is best to start with dynamic memory allocation and do some performance testing to see if you need to set limits or specify memory allocation manually.
Post #507147
Posted Tuesday, May 27, 2008 12:24 PM


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Tend to agree with Michael. Monitor and observe the system. AWE isn't needed for 64-bit and my guess is SQL will keep building cache and run to 30GB unless you limit it.







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Post #507165
Posted Tuesday, May 27, 2008 2:31 PM
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To get the total current size of your buffer pool run the following:

SELECT
SUM( multi_pages_kb +
virtual_memory_committed_kb +
shared_memory_committed_kb +
awe_allocated_kb ) AS [Used by BPool, KB]
FROM
sys.dm_os_memory_clerks
WHERE
[type] = 'MEMORYCLERK_SQLBUFFERPOOL'


Taken from INSIDE MICROSOFT SQL SERVER 2005, QUERY TUNING AND OPTIMIZATION by Kalen Delaney at el., which contains a good discussion of memory issues.

Another good tool is DBCC MEMORYSTATUS. It will give you the current size of the buffer pool, plus other components, such as the procedure cache.

Here is an excerpt from the output run on my server:

Buffer Counts Buffers
------------------------------ --------------------
Committed 786432
Target 786432
Hashed 722004
Stolen Potential 127447
External Reservation 0
Min Free 128
Visible 195584
Available Paging File 401426

Procedure Cache Value
------------------------------ -----------
TotalProcs 6878
TotalPages 54239
InUsePages 105


In the above sample, the procedure cache size is 54239 pages times 8 KB/page = 434 MB (roughly)


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Post #507261
Posted Tuesday, May 27, 2008 2:44 PM
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Steve Jones - Editor (5/27/2008)
Tend to agree with Michael. Monitor and observe the system. AWE isn't needed for 64-bit and my guess is SQL will keep building cache and run to 30GB unless you limit it.


It's true that because of the vast amount of virtual address space available in 64-bit, the need for AWE is greatly diminished.
However, memory allocated through AWE is locked in (will not get paged out), and that may be beneficial for app performance even in a 64-bit environment (albeit at the risk of starving other processes off of needed memory).


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Post #507274
Posted Tuesday, May 27, 2008 11:52 PM


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You need AWE to prevent memory stealing by the OS.
Also make sure you have a minimum and maximum size. Don't set the maximum size to unlimited, or SQL will compete with your OS for the last MBs.
We have the same configuration and our max memorysize is 28GB (min size is 16GB)

Also, be aware of memory trashing if you do a large OS filecopy on that server.
You also get memory messages in your logfile when adding/deleting databases/snapshots, but these are ok.


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Post #507437
Posted Wednesday, May 28, 2008 7:37 AM


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I agree with Wilfred van Dijk. Wilfred van Dijk has explined very clearly.

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Post #507669
Posted Wednesday, May 28, 2008 8:01 AM
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Wilfred van Dijk (5/27/2008)
You need AWE to prevent memory stealing by the OS.
Also make sure you have a minimum and maximum size. Don't set the maximum size to unlimited, or SQL will compete with your OS for the last MBs.
We have the same configuration and our max memorysize is 28GB (min size is 16GB)

Also, be aware of memory trashing if you do a large OS filecopy on that server.
You also get memory messages in your logfile when adding/deleting databases/snapshots, but these are ok.


Memory stealing is not a concern, unless there are other non-OS essential apps running on the server, correct? (I'm thinking Exchange for example).

Are there other occasions where mem stealing would be an issue?


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Post #507683
Posted Wednesday, May 28, 2008 9:02 AM


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If you don't enable AWE on a 64bit server you can get errors like "A significant part of sql server process memory has been paged out. This may result in performance degradation". for example, this can happen if you copy a lage filebackup to another server.
As a result, al your SQL processes are suspending, but I would say dying (I've had that experience)

Read the following articles:

http://blogs.msdn.com/psssql/archive/2007/05/31/the-sql-server-working-set-message.aspx
http://support.microsoft.com/kb/918483
http://msmvps.com/blogs/omar/archive/2007/09/19/a-significant-part-of-sql-server-process-memory-has-been-paged-out-this-may-result-in-performance-degradation.aspx
http://www.mcse.ms/message2444910.html
http://blogs.msdn.com/slavao/archive/2005/04/29/413425.aspx


Wilfred
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