The resource pressure changed from %1 to %2. Statistics: %3

This Warning event indicates that a system resource that is monitored by the back pressure feature has experienced a change in its utilization level.

The following system resources that are monitored on a Hub Transport server or Edge Transport server as part of the back pressure feature may appear in this event:

• Free space on the hard disk drive that stores the message queue database. This is known as queue database disk space.

• Free space on the hard disk drive that stores the message queue database transaction logs. This is known as queue database logging disk space.

• The number of uncommitted message queue database transactions that exist in memory. This is known as version buckets.

• The memory that is used by all processes. This is known as physical memory load.

For each monitored system resource, the following levels of resource utilization are applied:

• Normal   The resource is not overused. The server accepts new connections and messages.

• Medium   The resource is slightly overused. Back pressure is applied to the server in a limited manner. Mail from senders in the authoritative domain can flow. However, the server rejects new connections and messages from other sources.

• High   The resource is severely overused. Full back pressure is applied. All message flow stops, and the server rejects all new connections and messages.

If the event indicates that a system resource utilization level decreased from High to Medium or from Medium to Normal, no user action is required. If the event indicates that a system resource utilization level increased from Normal to Medium or from Medium to High, you can perform the following actions:

• Do nothing. The back pressure feature will stop accepting new messages and connections on the server. Existing messages will be delivered until the resources on the server are not overused.

• Free hard disk drive space. By default, the calculations that are used by back pressure to determine system resource utilization levels require a minimum of 4 GB of free space for queue database disk space and 500 MB of free space for queue database logging disk space. Uninstall nonessential programs or delete unnecessary files to increase the available free disk space.

• Increase the available physical memory. Install more memory or remove unnecessary processes from memory.

• Increase the default values of Normal, Medium, and High resource utilization levels for the particular resource that is monitored by the back pressure feature.

For more information about back pressure, see Understanding Back Pressure.

If you are not already doing so, consider running the tools that Microsoft Exchange offers to help administrators analyze and troubleshoot their Exchange environment. These tools can help you make sure that your configuration is in line with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. Go to the Toolbox node of the Exchange Management Console to run these tools now. For more information about these tools, see Toolbox in the Exchange Server 2007 Help.