December 1, 2007 at 6:24 pm
Hi ,
I have a question possibly a basic but need to clarify ,as 4 GB address space is divided into user and kernel partition for windows in x86 family of processors so here we are not talking about any thing physical memory(RAM) ? and it is all the disk space we are talking about?
and on the other hand for PAE and AWE we specifically talk about Physical Memory i.e RAM so any involvement of Virtual Memory there?
Appreciate your reply.
December 1, 2007 at 9:51 pm
Hi,
Check the followings links :
http://www.sql-server-performance.com/tips/awe_memory_p1.aspx
http://blogs.msdn.com/slavao/archive/2006/08/03/687573.aspx
http://technet.microsoft.com/en-us/library/ms187499.aspx
http://www.microsoft.com/technet/prodtechnol/sql/2005/tsprfprb.mspx
http://support.microsoft.com/kb/274750
http://technet.microsoft.com/en-us/library/ms190730.aspx
http://support.microsoft.com/default.aspx?scid=kb;en-us;274750
http://msdn2.microsoft.com/en-us/library/ms190673.aspx
Regards,
Ahmed
December 2, 2007 at 12:45 pm
Check the links and is there a point to what you are asking? Meaning why do you need to know?
If it's curiosity, there's a lot out there to read about. If it's configuration, there are some good references for what you should set.
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December 3, 2007 at 12:12 pm
Appreciate your reply and links ,one question on that
Inside SQL Server 2000 Memory Management by Ken Henderson says 'It is usually disk drive space. Specifically, it is space in the system paging file(s). That's how multiple applications can run on a system with 128MB of memory, each with a virtual address space of 4GB—it's not real memory,'
where as http://www.sql-server-performance.com/tips/awe_memory_p1.aspx article clearly says /3GB switch is physical memory only for VAS, so now question is
in this article http://technet.microsoft.com/en-us/library/ms189334.aspx process address space is paging file or RAM?
and if we dont have paging file >1GB how VAS is taken consideration for 2GB.
December 3, 2007 at 12:33 pm
Hi,
In the following article http://technet.microsoft.com/en-us/library/ms189334.aspx When you use /3G the kernel will use 1G from the RAM and other applications 3G from the RAM.
Regards,
Ahmed
December 3, 2007 at 12:34 pm
The /3GB switch is only for systems with 4 or more GB or physical RAM. This specifically determines how physical ram is allocated between the user and process spaces.
For all applications, they behave as if they're the only application on the system, with 2GB of RAM and 2GB of process space. However the space usually doesn't exist physically, so the OS takes care of mapping the"virtual" memory, to real physical memory, often backing this with page file space.
This is mapped, meaning that if your application thinks it's accessing memory from 3.5-3.6GB, the OS takes care of mapping this back to actual physical locations in memory and as needed, on disk.
You don't need to worry about it.
Is there something specific you are trying to do with SQL Server, or just wondering how this works? There are better forums for figuring out how this works.
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December 4, 2007 at 12:57 pm
Thanks ,appreciate your time , so it looks 2GB of kernel and 2 GB for application is taken care by O/S and initially it is just mapping to physical memory not actual allocation , and if page file size is small then o/s manipulates it self for VAS to give some physical mapping ,please confirm if i understood wrong?
we are working to check the Memory pressure for one of the server ,all the memory counters look ok but wondering for VAS and how page file on system helps?
if this is not the correct forum to discuss that please re-direct me to the correct one.
December 4, 2007 at 3:17 pm
That's the general idea. The pagefile helps swap out physical memory and if you have high pagefile reads/writes and memory reads/sec along with disk activity, you can be seeing memory pressure. However the 2GB allocation and /3GB switch won't help if you don't have physical memory.
You really need a baseline on systems so you can see if counters are reading high when looking for memory pressure. Too many counters are relative to how your system normally performs.
You can read more here:
http://blogs.msdn.com/slavao/archive/2005/02/19/376714.aspx
http://www.sqlmag.com/Article/ArticleID/43117/sql_server_43117.html
http://www.sql-server-performance.com/tips/performance_monitor_memory_counter_p1.aspx
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