Understanding the effects of virtual memory

For the best performance, the Meridian application server needs to allocate sufficient memory for two purposes:

• A database cache for each active vault on the server
• Session data for each active user connected to a vault on the server.

If there is not sufficient physical memory for these purposes, together with all of the other applications running on the server, virtual memory is used to store the data temporarily on disk, which is much slower than physical memory and reduces system performance. This is why we recommend a server dedicated for use by Meridian as described in Understanding the effects of a dedicated server.

By default, each 32-bit Windows application can access a maximum of 2 GB of virtual memory (3 GB if the /3GB switch is enabled) when run on a 32-bit Windows operating system. Depending on the number of concurrent users and the size of the database caches, Meridian may request more than this amount of memory from the operating system, and the service can fail with an “Out of Memory” error.

Note    The following task 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.

To optimize virtual memory usage, there are several things you can do:

1. Ensure that the Windows page file is large enough to meet the needs of all applications running on the server. We recommend that it be at least as large as the installed physical RAM on the server. We highly recommend that you assign the page file to a different drive than the drive where the Meridian vaults are located.
2. Determine how much actual virtual memory is requested by Meridian by monitoring the AMEDMW instance of the Virtual Bytes counter of the Process object with Performance Monitor as described in Configuring the Windows Performance Monitor. Also monitor the Available Mbytes counter of the Memory object.
3. If the amount of virtual memory used by Meridian approaches 2 GB (3 GB if the /3GB switch is enabled) before the maximum expected number of users is reached, reduce the amount of memory allocated to database caches so that it can be used to accommodate more users.

To adjust the database caches:

1. Start using the system with a conservative number of users. Use Performance Monitor as described in step 2 to monitor the amount of virtual memory requested by Meridian during peak production hours.
2. If Available Mbytes drops below 300 MB before the maximum virtual memory consumption is reached, reduce the Maximum Cache Size option of one or more vaults to free memory as described in Configuring the MaximumCacheSize setting.
3. Monitor the amount of virtual memory used as additional users are allowed access to the system.
4. Repeat steps a through c until all users are connected to vaults.

If reducing the cache sizes causes the performance to become unacceptable, you should consider switching to a newer version or different edition of Windows Server (for example, 64-bit), if possible, to access additional physical and virtual memory.

Note    Restarting the AutoManager EDM Server service will free any unused virtual memory. If the virtual memory usage measured in step 2 approaches 2 GB (3 GB if the /3GB switch is enabled) and cannot be lowered by reducing the cache sizes without adversely affecting performance, we recommend restarting the service after business hours, daily if necessary, as a last resort to providing additional virtual memory.

4. In order to manage all of the available virtual memory, Windows uses a system page table to track where in the virtual memory page file each piece of information is located. Unused entries in this table are known as free system page table entries (PTEs) and can be monitored with the Free System Page Table Entries counter of the Memory object with Performance Monitor as described in Configuring the Windows Performance Monitor. The amount of PTEs can be increased by enabling the option described in Understanding the effects of the Windows /userva switch.

The allocation table of Windows 32-bit versions is limited to 4 GB. By default, the operating system allows 2 GB of virtual memory for all applications and 2 GB for its own processes. However, it is possible to change these allocations as described in Understanding the effects of the Windows /3GB switch. If more than 4 GB of physical RAM is installed in the server, you should consider the recommendations described in About the High Performance Option.