Microsoft KB Archive/247775

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XADM: Exchange Server Unavailable at Regular Intervals, PerfMon Shows Spike

Article ID: 247775

Article Last Modified on 10/27/2006


  • Microsoft Exchange Server 5.5 Standard Edition

This article was previously published under Q247775

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry


When you are administering Microsoft Exchange Server 5.5, you may receive reports every six hours that users are unable to gain access to their inboxes. This lasts for about 15 minutes and occurs on an Exchange Server that has many more inboxes than the other servers in the site.

When you examine the MSExchangeDS\Pending Replication Synchronization counter in Performance Monitor, you see that the counter records abnormally high numbers during the problem time periods.


This behavior can occur when the server's Directory service is unable to handle all of the remote procedure call (RPC) requests it receives.


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.

To resolve this issue, change two values in the registry. Follow these steps:

  1. Start Registry Editor (Regedt32.exe).
  2. Locate the Max Threads(EXDS+NSP+DSA) value entry under the following registry key:

  3. Double-click the value and set it to the equivalent of (50 * number of processors) + 30.
  4. Locate the Replicator Maximum concurrent read threads value entry under the following registry key:

  5. Double-click the value, and then set it to zero (0).
  6. Quit Registry Editor.


When you examine the Period-Rep-Sync-Times attribute on the site properties dialog box in Raw mode, you see that the schedule is set at every six hours. This is the interval at which each server in the site sends out requests to get Directory updates from within the site.

Keywords: kbprb KB247775