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Intermittent Database connectivity issue with Citrix Xendesktop 7.6 delivery controller

Sudipta De1709159584



We are experiencing intermittent database connectivity issue with Citrix Delivery Controller 7.6. It is happening mainly during start of the day while most of the users logs into the Citrix farm. We have total 4 Delivery controller across two datacenter (2 in each DC) and getting the below database connectivity event log from all delivery controller at the same time.


The connection between the Citrix Broker Service and the database has been lost. 
Error details: 
Exception 'Execution Timeout Expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.' of type 'System.Data.SqlClient.SqlException'. 
Ensure that the database is correctly configured and accessible.


DB server is also running in cluster mode.


This connectivity issue is getting resolved within 1 minutes and we use to get a below event log stating that connectivity is restored. Though error keeps on coming throughout the day. 


The connection between the Citrix Broker Service and the database has been restored.


But users are getting "cannot start the app" error whoever is trying to launch any application at that time interval. There is no packet drop observed between Citrix delivery controller and DB server. DB team has observed, there are transaction blockage(waiting for other transactions) at the time of issue  and most of the transactions are getting time out at that time interval. 


We have already changed the time out value and min Pool size to 150 and 20 respectively in all delivery controllers inside registry. But still there is no improvement noticed. 


If anyone noticed this issue or got any resolution, please share . It will be helpful.




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I believe 7.6 uses connection leasing when the database goes down rather than local host cache (which is available again in 7.15). Users won't be able to launch new instances of applications if the database connection is down. It sounds like the database is too busy to service requests however your SQL DBA will be able to monitor this and tell you if this is the case.



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SQL DBA lads are not getting any authentication failure. All logon requests from all delivery controller machine account is able to login successfully. But transactions are getting timeout. Also noticed that it is not happening everyday. It is totally sporadic and very tough to derive a trend. DB server utilization is normal and there is no network issue observed. 

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We have Microsoft SQL server running in cluster mode on Windows cluster. No mirroring or always on configured. 


As per Citrix Director we got generic Machine failure error message.  We are still facing the issue. Have raised a call with Citrix but did not get any permanent fix for this issue yet.

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