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Is this a memory limit issue?

Posted on 2009-04-09
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Last Modified: 2012-05-06
Hi,
We have been experiencing degrading performance on our SQL 2000 std. database. We are running on windows 2003 std, with 4GB of ram. our larger (and most often used) databases have gone over 2GB each.

Checking memory usage, we never see the system going over 1.8GB, so figured that memory could not (yet) be the issue becouse SQL would go up to atleast 2gb... but... this is so close to it that it might actually be that limit already.

What do you think?
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Question by:pdvd
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RiteshShah earned 250 total points
ID: 24105275
Memory could be an issue but have you checked your indexes properly? tried to defrag and re-index it? that might give you boost up in your performance.
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by:Guy Hengel [angelIII / a3]
ID: 24105308
sql server will try to use as much memory as possible, this is by design.
as your box has 4GB, if sql server uses "only" 1.8GB there is no problem so far, except that you might check to allow more than the 2GB limit...

anyhow:
* check the max memory setting of you sql server instance, usually it's set to the default (big number) to allow to take it all.
  -> change that on your box to 3500, which means 3500MB = 3.5GB.

* check if AWE is enabled or not.
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by:rentonc
rentonc earned 200 total points
ID: 24105309
have you changed your boot ini file to use more memory for your applications by default 2gb is reserved for the os leaving 2gb for applications, W2K3 only needs around 1Gb of memory reserving for the os so you can tell it to use the full 3gb for applications
see here:-
http://technet.microsoft.com/en-us/library/bb124810.aspx

thanks
Chris
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by:RiteshShah
ID: 24105496
every suggestion of angelIII and rentonc are really worth looking and really helpful to boost up the speed but I guess this is not a reason that you were getting good performance and now it is degraded. there may be a Index or trigger causing a problem as per me and for further help, let this question open for other expert.

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Author Comment

by:pdvd
ID: 24105542
so....
Thank you all! I have a bunch of questions though:
1) RiteshShah: I will re-index all tabled, need to do this at night though, can not test results yet.
2) Angellll / Rentonc: I have made no special modifications to allow over 2GB's of memory. the config as it stands: basic 2003 std. install with basic SQL 2000 std. install. no modifications to the boot.ini. I checked memory settings on SQL server, and it is set to use up to 3571MB, I have not set AWE (and do not yet know where to find that..

Search the web I found some confusing info on memory / windows / database servers:
http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx states:

Windows XP Professional and Windows Server 2003 Memory Support.
The maximum amount of memory that can be supported on Windows XP Professional and Windows Server 2003 is also 4 GB. However, Windows Server 2003, Enterprise Edition supports 32 GB of physical RAM and Windows Server 2003, Datacenter Edition supports 64 GB of physical RAM using the PAE feature.

The virtual address space of processes and applications is still limited to 2 GB unless the /3GB switch is used in the Boot.ini file. When the physical RAM in the system exceeds 16 GB and the /3GB switch is used, the operating system will ignore the additional RAM until the /3GB switch is removed. This is because of the increased size of the kernel required to support more Page Table Entries. The assumption is made that the administrator would rather not lose the /3GB functionality silently and automatically; therefore, this requires the administrator to explicitly change this setting.

The /3GB switch allocates 3 GB of virtual address space to an application that uses IMAGE_FILE_LARGE_ADDRESS_AWARE in the process header. This switch allows applications to address 1 GB of additional virtual address space above 2 GB.


Does this mean, that no matter what OS/DBS combo I choose, I will not be able to use over 3GB for my DBS??? that would be rediculous, and I probably misunderstand.

We are planning to migrate to SQL2008, details I'll post in a seperate question, but would you expect a significant performance boost, would it be able to use more memory?
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Author Comment

by:pdvd
ID: 24105566
And, another thing that is still not clear to me...
a) In my current config, (not having enabled AWE and running on SQL 2000 ***Standard Edition***), is SQL now using all memory available to it when it uses 1,8GB? is this effectively the 2GB limit?
b) if so... if I would set the AWE options, would this version SQL even be able address more than the 2GB? or would I need to upgrade to either 2000 Enterprise or 2005/2008?
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by:rentonc
ID: 24155949
With W2K3 std edition you cannot use more than 4GB of memory no matter how much you physically install.
At the moment your application (SQL) is limmited to using 2GB of the 4GB - this is the default behaviour of W2K3 - if you add the /3GB switch in the boot ini then SQL can use 3Gb of the 4GB.

With enterprise most of the spare memory is used for caching disk access for better performance

There is a very good description here:-
http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Server/2003_Server/Q_23700599.html

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Author Comment

by:pdvd
ID: 24258546
Hey all,
Thank you for your responses...
I found this artical that also has some nice insights in to mem usage, and helps explain the reasons why SQL does not seem to use all memory... http://www.eraofdata.com/blog/tag/memtoleave/

It took some work, but I also rebuild the indexes, and that seems to have helped a little at least.

We will soon be upgrading to a Windows 2003 64bit / SQL 2008 environment.. This should take us away from all the memory limitations.

Thanks again!
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