Understanding the effects of the Windows /userva switch

Note    The following applies to Meridian 32-bit editions when run on a Windows 32-bit operating system only. For information about running Meridian 32-bit and 64-bit editions on a Windows 64-bit operating system, see BlueCielo support for 64-bit Windows operating systems in the BlueCielo knowledge base.

Under some conditions, the Meridian application server may become unstable after implementing the /3GB switch described in Understanding the effects of the Windows /3GB switch resulting in “Out of Memory” errors. This may happen particularly with large numbers (> ~75) of simultaneous users and is caused by insufficient free system page table entries (PTEs) available to the operating system on the server.

When the /3GB switch is implemented on the Meridian application server, the available operating system kernel memory is limited to a maximum of 1 GB. This can cause free PTEs to fall below workable levels. You can enable a reserve of free PTEs to be used under high load conditions by adding the /userva switch to the boot.ini file of the EDM server and specifying a maximum value (in MB) for user mode (application) memory.

For example, adding /userva=2900 to boot.ini will reduce the 3072 MB (3 GB) of application memory allocated by the /3 GB switch to 2,900 MB. This effectively reassigns 172 MB to the Windows kernel (172 MB + 1024 MB = 1,196 MB total) to be used when additional PTEs are required. Specifying a lower value for /userva will result in even more available Windows kernel memory.

You can monitor the number of free PTEs on the Meridian application server with Windows Performance Monitor and the Free System Page Table Entries counter of the Memory object as described in Configuring the Windows Performance Monitor. For more information on using Performance Monitor, see Windows Help and the links below.

Note    There is a Windows Server 2003 bug regarding Performance Monitor reporting the wrong amount of Free System Page Table Entries. Read more about the Performance Monitor reporting error at The Performance tool does not accurately show the available Free System Page Table entries in Windows Server 2003.