This article describes how to adjust the polling interval to change how often a member server queries a server farm’s data store to synchronize its local host cache.

This is crucial knowledge if the data store is experiencing high CPU usage.

Background

When a change is made to the farm’s data store, a notification to update the local host cache is sent to all the servers in the farm. However, it is possible for some servers to miss an update because of network problems. Member servers periodically query the data store to determine if any changes have been made since the server’s local host cache was last updated. If changes are detected, the server requests the changed information.

Most changes made through the Presentation Server Console are written to the data store. When you open the console, it connects to a specified server. The Citrix IMA Service running on the server performs all reads and writes to the data store for the console. If the data store is experiencing high CPU usage when there should not be significant reads or writes to the data store, it is possible that the data store is not powerful enough to manage a query interval of 30 minutes. To determine whether or not the data store query interval is causing the high CPU usage on the data store, you can set the query interval to a very large number and test CPU usage. If the CPU usage returns to normal after you set a large query interval, the data store query interval is probably the cause of the high CPU usage. You can adjust the query interval by trial and error.

To test the query interval, set the interval to 60 minutes and then restart all the servers in the farm. If the data store is still experiencing constant high CPU usage, increase the query interval. If the CPU usage returns to normal, you can try a smaller value. Continue these adjustments until data store CPU usage is normal.

Important! Do not set the data store query interval higher than necessary. This interval serves as an important safeguard against lost updates. Setting the interval higher than necessary can cause delays in updating the local host cache of the farm’s member servers.

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Instructions

You can adjust the interval by which member servers query the farm’s data store for missed changes. The default interval is 30 minutes.

Caution! This procedure requires you to edit the registry. Using Registry Editor incorrectly can cause serious problems that might require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Back up the registry before you edit it.

Configure the interval using the following registry key on each server you want to adjust, with the value expressed in hexadecimal notation:
HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\IMA\
DWORD: DCNChangePollingInterval
Value: 0x1B7740 (default 1,800,000 milliseconds)
Note: You must restart the IMA Service for this setting to take effect.

This article describes how to adjust the polling interval to change how often a member server queries a server farm’s data store to synchronize its local host cache.

Citrix Documentation - Tuning Local Host Cache Synchronization

Citrix Video - How to Change the Local Host Cache Polling Interval on a XenApp Server