Max Memory Settings for SQL Server 2005/2008

It is pretty important to make sure you set the Max Server memory setting for SQL Server 2005/2008 to something besides the default setting (which allows SQL Server to use as much memory as it wants, subject to signals from the operating system that it is under memory pressure). This is especially important with larger, busier systems that may be under memory pressure.

This setting controls how much memory can be used by the SQL Server Buffer Pool.  If you don’t set an upper limit for this value, other parts of SQL Server, and the operating system can be starved for memory, which can cause instability and performance problems. It is even more important to set this correctly if you have “Lock Pages in Memory” enabled for the SQL Server service account (which I always do for x64 systems with more than 4GB of memory).

These settings are for x64, on a dedicated database server, only running the DB engine, (which is the ideal situation).

Physical RAM                        MaxServerMem Setting

2GB                                           1500

4GB                                           3200

6GB                                           4800

8GB                                           6400

12GB                                         10000

16GB                                         13500

24GB                                         21500

32GB                                         29000

48GB                                         44000

64GB                                         60000

72GB                                         68000

96GB                                         92000

128GB                                       124000

If you are running other SQL Server components, such as SSIS or Full Text Search, you will want to allocate less memory for the SQL Server Buffer Pool. You also want to pay close attention to how much memory is still available in Task Manager. This is how much RAM should be available in Task Manager while you are under load (on Windows Server 2003):

Physical RAM            Target Avail RAM in Task Manager

< 4GB                               512MB – 1GB

4-32GB                              1GB – 2GB

32-128GB                            2GB – 4GB

> 128GB                              > 4GB

You can use T-SQL to set your MaxServerMemory setting. The sample below sets it to 3500, which is the equivalent of 3.5GB. This setting is dynamic in SQL Server 2005/2008, which means that you can change it and it goes into effect immediately, without restarting SQL Server.

–Turn on advanced options

EXEC sp_configure ‘Show Advanced Options’ ,1;

GO

RECONFIGURE;

GO

–Set max server memory

EXEC sp_configure ‘max server memory (MB)’ ,10000;

GO

RECONFIGURE;

GO

–See what the current values are

EXEC sp_configure;

You can also change this setting in the SSMS GUI, as you see below: