Back Pressure in Exchange 2007

This article just give you the basic idea what is back pressure and moreover this article is based on the symptoms about checking whether your exchange 2007 server is effected by back pressure. There might be a better solution you will get regarding this issue, if you have any other solution apart from this article which I mentioned here please add it in the comments.

Lets clear up the basic concept

Back Pressure:
  Back Pressure is a system resource monitoring feature which will monitor available disk space and available memory. It is the feature of the Microsoft Transport Service which will run in the Edge Server and Hub Server.

The following system resources are monitored as part of the back pressure feature:

• Free space on the hard disk drive that stores the message queue database.
• Free space on the hard disk drive that stores the message queue database transaction logs.
• The number of uncommitted message queue database transactions that exist in memory.
• The memory that is used by the EdgeTransport.exe process.

The memory that is used by all processes:
For each monitored system resource on a Hub Transport server or Edge Transport server, the following three 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.

Location of this back pressure configuration:
 Back Pressure configuration option you will get in the file called EdgeTransport.exe.config file which is located under C:\program files\microsoft\Exchange Server\Bin

Figure1

Who is Responsible for this alert:

Responsible for generating this monitoring alert is “EnableResourceMonitoring “ by default it is set to True.  But you can change it to false to wave off.
Microsoft Recommendation is not to Set it to False. Because this is a monitoring process and even a precaution for you to take care before it get worst.

When you open the EdgeTransport.exe.config, you can see this are the following parameters for back pressure

      <add key="EnableResourceMonitoring" value="True" />
      <add key="ResourceMonitoringInterval" value="00:00:02" />
      <add key="PercentageDatabaseDiskSpaceUsedHighThreshold" value="0" />
      <add key="PercentageDatabaseDiskSpaceUsedMediumThreshold" value="0" />
      <add key="PercentageDatabaseDiskSpaceUsedNormalThreshold" value="0" />
      <add key="PercentageDatabaseLoggingDiskSpaceUsedHighThreshold" value="0" />
      <add key="PercentageDatabaseLoggingDiskSpaceUsedMediumThreshold" value="0" />
      <add key="PercentageDatabaseLoggingDiskSpaceUsedNormalThreshold" value="0" />
      <add key="PercentagePrivateBytesUsedHighThreshold" value="0" />
      <add key="PercentagePrivateBytesUsedMediumThreshold" value="0" />
      <add key="PercentagePrivateBytesUsedNormalThreshold" value="0" />

Table 1 shows the general configuration options for back pressure that are available in the EdgeTransport.exe.config file.

Table 1   General back pressure options

 Table 2   Options for monitoring the free hard disk drive space for the message queue database

I installed Exchange 2007 in a co-existence environment. I tried to send a mail to exchange 2007 box and it is getting saved as a Draft. Checked the message tracking no information available for this particular mail and because it has not left the outlook itself .
When I tried to send a mail from exchange 2003 to exchange 2007 in the message tracking - it is telling me that it has been delivered to remote queue. So something is stopping the mail on exchange 2007 server end.

Figure 2

I checked the eventlog and found this event id : 15002

The following list describes the event log entries that are generated by specific back pressure events in Exchange 2007 RTM:

Event log entry for changes in resource utilization level
Event Type: Warning
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15001
Description: The resource pressure changed from Previous Utilization Level to Current Utilization Level.

Event log entry for constantly high resource utilization levels
Event Type: Warning
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15002
Description: The resource pressure is constant at High.

Event log entry for changes in memory utilization level by the EdgeTransport.exe process
Event Type: Warning
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15003
Description: Private bytes consumption changed from Previous Utilization Level to Current Utilization Level.

Detailed description:

Event Type: Warning
Event Source: MSExchangeTransport
Event Category: ResourceManager
Event ID: 15002
Date:  11/21/2007
Time:  11:18:59 AM
User:  N/A
Computer: E2K7
Description:
The resource pressure is constant at High. Statistics:

Queue database and disk space ("C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\mail.que") = 63% [High] [Normal=45% MediumHigh=47% High=49%]

Queue database logging disk space ("C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\") = 63% [Normal] [Normal=89% MediumHigh=91% High=93%]

Version buckets = 1 [Normal] [Normal=40 MediumHigh=60 High=100]

Private bytes = 11% [Normal] [Normal=71% MediumHigh=73% High=75%]

Physical memory load = 49% [limit is 94% to start dehydrating messages.]

Inbound mail submission from other Hub Transport servers, the Internet, the Pickup directory, the Replay directory, and the Mailbox server, if it is on a Hub Transport server, has stopped.
Loading of e-mail from the queuing database, if available, continues.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

Event Type: Warning
Event Source: MSExchangeMailSubmission
Event Category: MSExchangeMailSubmission
Event ID: 1009
Date:  11/21/2007
Time:  11:20:53 AM
User:  N/A
Computer: E2K7
Description:
The Microsoft Exchange Mail Submission service is currently unable to contact any Hub Transport servers in the local Active Directory site. The servers may be too busy to accept new connections at this time.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

Back Pressure Logging Information in Exchange 2007 SP1
The following list describes the event log entries that are generated by specific back pressure events in Exchange 2007 SP1:
Event log entry for an increase in any resource utilization level
Event Type: Error
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15004
Description: Resource pressure increased from Previous Utilization Level to Current Utilization Level.

Event log entry for a decrease in any resource utilization level
Event Type: Information
Event Source: MSExchangeTransport
Event Category: Resource Manager
Event ID: 15005
Description: Resource pressure decreased from Previous Utilization Level to Current Utilization Level.
 

15002 event id will show you the back pressure precentage.
Checked the free space it is just 2.53 GB only
Tried telnet 127.0.0.1 : Insufficient System Resources
Figure 3

• Disabled the resource Monitoring of Back Pressure but it is not a solution at all.

Workaround solution for me:

• Final step which i took is recreating the whole OS which should  have  4 GB of minimum free space atleast (a disaster workaround solution for me ) for my vmware os

But in real time you need to change the location of Queue Database path and log file path as a part of a solution

Go to EdgeTransport.exe.config file => right click => Edit => open with notepad and change the following two lines:

Search for this following key :
<add key="QueueDatabasePath" value = "C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue" />
      <add key="QueueDatabaseLoggingPath" value = "C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue" />

Then change it to desired location

<add key="QueueDatabasePath" value = "D:\Exchange Server\TransportRoles\data\Queue" />
      <add key="QueueDatabaseLoggingPath" value = "D:\Exchange Server\TransportRoles\data\Queue" />

Then need to restart the Microsoft Exchange Transport Service.

Note : 4 GB free space need for mail submission queue in RTM version but after the release of service pack1 Microsoft Changed the default setting to 500 MB.

 So before you could implement the exchange hub or edge server make sure that you have atleast 4 GB of free space for submission of the mail in RTM Version Exchange in the vmware lab setup and in realtime also.

 I would like to thanks to Anderson Patricio who had released an article regarding this back pressure issue
Understanding the Back Pressure Feature in Exchange Server 2007 in msexchange.org
http://www.msexchange.org/articles_tutorials/exchange-server-2007/management-administration/understanding-back-pressure-feature-exchange-server-2007.html

 For in depth understanding about the back pressure process please go through the above article and plus the ms technet link which I added in this blog

I would like to thanks to Mark Arnold who had shared his view in his blog regarding this issue,
http://markarnold.blogspot.com/2007/04/exchange-2007-queue-database-moving-it.html

Reference took from:

Understanding Back Pressure
http://technet.microsoft.com/en-us/library/bb201658.aspx

Hope it is valuable information for you all and thank you for going through this article.