IsAlive LooksAlive Process for SQL Cluster Resources

‘’ For the SQL Server resource, the LooksAlive check (also referred to as Basic resource health check in Windows Server 2008) will verify that the SQL Server service is running on the online node every 5 seconds by default. If the LooksAlive check fails, the Windows Server cluster service performs an IsAlive check to confirm the failure.

The IsAlive check (also referred to as Thorough resource health check in Windows Server 2008) runs every 60 seconds and verifies the cached result of an internal IsAlive process in the SQL Server resource DLL.

An internal process in the SQL Server resource DLL handles all connection and execution of the underlying IsAlive logic. It contains extensive retry logic to verify any connectivity or execution failures. Upon successful connection to the SQL Server, the internal IsAlive check executes SELECT @@SERVERNAME every 60 seconds to determine whether SQL Server is online. If this query fails, the internal process runs additional retry logic to avoid stress-related failures. If the retry logic also fails, the internal process shuts down the SQL Server service and updates a cached result that causes the next LooksAlive and IsAlive checks to fail.’’

http://download.microsoft.com/download/6/9/D/69D1FEA7-5B42-437A-B3BA-A4AD13E34EF6/SQLServer2008FailoverCluster.docx

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