Section 15.9. AWE Support with Windows

15.9. AWE Support with Windows

When working with Windows 2000, the total addressable memory can be up to 64GB; therefore, the maximum buffer pool sizes that can be created on Windows equals 64GB minus the memory used by the operating system and other DB2 memory allocations (assuming that the server is dedicated to DB2). The support for large memory addressing on 32-bit Windows is provided by the Microsoft Address Windowing Extensions (AWE). Through AWE, the Windows 2000 Advanced Server provides support for up to 8GB of memory addressing, while the Windows 2000 Data Center Server provides support for up to 64GB of memory.

To take advantage of memory addresses above 2GB, both DB2 and Windows 2000 must be configured correctly to support AWE. To address up to 3GB of memory, you must set the /3GB Windows 2000 boot option. To enable access to more than 4GB of memory via the AWE memory interface, you must set the /PAE Windows 2000 boot option. To verify that you have the correct boot option selected, under the Control Panel, select System, and then select Startup and Recovery. From the drop-down list you can see the available boot options. If the boot option you want is selected (/3GB or /PAE), then you are ready to proceed to the next task: setting up AWE support. If the option you want is not available, you must add the option to the boot.ini file on the system drive. The boot.ini file contains a list of actions to be done when the operating system is started. Add /3GB, /PAE, or both (separated by blanks) at the end of the list of existing parameters. Once you have saved this changed file, you can verify and select the correct boot option as described.

Windows 2000 also has to be updated to associate the right to lock pages in memory with the user ID that was used to install DB2. To set this, once you have logged on to Windows 2000 as the user who installed DB2, under the Start menu on Windows 2000 select the Administrative Tools folder, and then the Local Security Policy program. Under the local policies, you can select the user rights assignment for lock pages in memory.

DB2 also requires the setting of the DB2_AWE registry variable so you can take advantage of the larger memory addressing. You must set this registry variable to the buffer pool ID of the buffer pool that will be larger than 3GB and needs AWE support, as well as the number of physical pages and the address window pages to be allocated for the buffer pool.

The buffer pool ID is found in the BUFFERPOOLID column in the catalog view SYSCAT.BUFFERPOOLS. The number of physical pages to allocate should be less than the total number of available pages of memory, and the actual number chosen will depend on the working environment. For example, in an environment where only DB2 and database applications are used on the server, usually select a value between one half of the available memory up to one GB less than the available memory. In an environment where other nondatabase applications are also running on the server, these values will need to be reduced to leave memory available for the other applications. The number used in the DB2_AWE registry variable is the number of physical pages to be used in support of AWE and for use by DB2. The upper limit on the address window pages is 1.5GB, or 2.5GB when the /3GB Windows 2000 boot option is in effect.