XADM: How The Active Directory Connector Polling Period Works (253825)

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The ADC works based on a polling mechanism, instead of a notification mechanism, to identify what has changed in a directory. Every time that the ADC tries to identify changes in the Active Directory or in the Exchange Server directory, the ADC queries for what has changed after a specified time, instead of being notified by those components when something changes. This is done for two reasons:

• To avoid a loss of changes if the service is not running at the moment that someone changes a user's information.
• To avoid the need for the ADC to work uninterruptedly, which stresses the processor and the Active Directory.

Each time that the ADC starts to poll information from one server to another is called a cycle. On a two-way Connection Agreement, a cycle has two stages. First, the ADC searches for modifications on the Exchange Server computer, and after the ADC finishes, it searches for modifications on the Active Directory server.

To configure the polling period, perform the following steps:

1. Open the Active Directory Connector Microsoft Management Console (MMC) snap-in.
2. Open the properties for a Connection Agreement.
3. Click on the Schedule tab. Choose one of the three following basic options:
   • Never. The Connection Agreement never runs and does not propagate modifications, additions, and deletions. This option is useful if you want to track down a problem and want to "turn off" all of the Connection Agreements except one.
   • Scheduled. Use the grid to specify when you want the Connection Agreement to run. You can also choose the resolution that you want the grid to display at, either 15 minutes or 1 hour. Each box that you select causes the ADC to start to poll at that moment, but this does not mean that the polling lasts only 15 minutes or 1 hour; the ADC only stops when it finishes polling. Also, if you select two polling periods that are adjacent in 15-minute resolution and the first cycle takes longer than 15 minutes, the ADC ignores the second period and continues the work that it started on the first period.
   • Always. The ADC searches for modifications on both servers every 5 minutes.

If one cycle has a lot of modifications, additions, and deletions to perform, the ADC can easily stress the Active Directory with ADC-only searches, modifications, additions, and deletions. This can cause other programs that depend on Active Directory to work very slowly.

To avoid this situation, the ADC has a "Sync Sleep Delay" mechanism. This mechanism causes the ADC to pause each Connection Agreement after 5 minutes of consecutive replication, sleep for 5 minutes, and then resume replication again.

You can change the values for sleep and for continuous synchronization by using registry keys:

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:

   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSADC\Parameters

3. On the Edit menu, click Add Value, and then add the following registry values:

   Value Name: Sync Sleep Delay (secs)
   Data Type: REG_DWORD
   Value: The default is 300 seconds
   
   Value Name: Max Continuous Sync (secs)
   Data Type: REG_DWORD
   Value: The default is 300 seconds

4. Quit Registry Editor.

Purpose of the Max Continuous Sync (secs) Registry Value

The Max Continuous Sync (secs) value defines the maximum amount of time that the ADC replicates uninterruptedly. If you change this value to 1200 (20 minutes), the ADC works for 20 minutes, then sleeps for 5 minutes, then works another 20 minutes, and so on. Remember, this only takes effect if there are a fairly large amount of modifications to be done. In the current cycle, if only a few entries need to be modified, the ADC performs the replication and finishes before the Max Continuous Sync (secs) value is reached and the mechanism is not triggered.

Purpose of the Sync Sleep Delay (secs) Registry Value

The Sync Sleep Delay (secs) value defines the amount of time that the ADC sleeps after it reaches the Max Continuous Sync (secs) value, and also the amount of time before the next cycle starts. For example, if you change the Sync Sleep Delay (secs) value to 60 (1 minute), and you set your Connection Agreement to schedule Always, a new cycle starts to search for modifications on both servers every 60 seconds.

Also, if the amount of modifications that need to be done causes replication to take longer than the Max Continuous Sync (secs) value of 5 minutes, the ADC replicates for 5 minutes, sleeps 1 minute, replicates 5 minutes, sleeps 1 minute, and so on.

Both registry keys are loaded when the service starts, so you need to restart the service for these values to take effect.

NOTE: Use these registry keys very carefully. If you set them too low or too high, they can degrade performance on the Exchange Server computer and on the Active Directory, with little or no improvement for replication.