PRB: OLAP Databases Larger Than 150 GB May Result in NT Kernel Out of Memory Errors (268362)

SYMPTOMS

When working with a large number of files or with particularly large cube files in OLAP services (over 150 GB total file sizes), errors indicating that the kernel has insufficient memory may occur.

You may observe this problem in the following ways:

On the Performance tab in Task Manager, Kernel Memory will be above 170 MB.
There may be failures from non-OLAP processes in Microsoft Windows NT.
There may be failures from OLAP server when attempting to read files from disk.

CAUSE

By default, OLAP files are opened in buffered mode. When files are opened in buffered mode, the Windows NT file cache consumes approximately 1 MB of kernel page pool memory for each 1 GB of file size. When working with large OLAP files, it is possible for the kernel to run out of memory.

WORKAROUND

In Analysis Services 2000, a registry entry named "UnbufferedThreshold" can be used to indicate a threshold size that determines whether a file is opened in buffered or unbuffered mode. This entry is created under the following key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\OLAP Server\CurrentVersion

The unit for this registry entry is number of megabytes; any file under the specified size is opened in buffered mode, and all others are opened in unbuffered mode.

MORE INFORMATION

A good guide for determining this file size is to perform a search of all files under the Data folder for your Analysis Services server and sort them by size (ascending). Select a set of files and press ALT+ENTER to get a Properties dialog box that shows the total size of the selected files. By using this method, you can determine the files that fit into the 150 GB group. Any files larger than the last file selected should be opened in unbuffered mode.

For example, if you find that all files under 6 GB in size have a sum total of 150 GB, then any files that are 6 GB and larger should be opened in unbuffered mode. In this case, create the "UnbufferedThreshold" registry entry and give it a value of 6000.

After setting this registry entry, stop and restart the Analysis Server service. On server restart, all files larger than 6000 MB will be opened in unbuffered mode.