How SQL Server clusters are detected online

Introduction to SQL Server cluster knowledge

Windows cluster installation

iSCSI-based SQL Server 2012 cluster Testing

Objective

The detection of a cluster is a call to a DLL resource, such as Windows self-contained resources such as shared storage, IP, network name, and DTC, which define the respective detection methods in Clusres.dll and periodically call DLL resources.

For SQL Server clusters, have their own DLL resources, for the corresponding detection, the first is to detect whether the SQL Server Cluster service is online, called LooksAlive, followed by the detection of the database is normal online, called IsAlive.

LooksAlive

LooksAlive default is 5 seconds to detect once, generally do not modify. is to detect whether the SQL Server service is in the startup state.

IsAlive

IsAlive default is 60 seconds to detect once, generally do not modify. SQL Server requires IsAlive detection because the SQL Server service is online and does not prove that SQL Server can respond well to client requests. Prior to SQL Server 2012, the IsAlive method was to link SQL Server, execute "SELECT @ @servername" and, if returned in a timely manner, would indicate normal.

The DLL resource for SQL Server 2012 calls the stored procedure "Sp_server_diagnostics" to perform a isalive check. The stored procedure returns the execution result to the DLL. By default, Sp_server_diagnostics is executed every 20 seconds. The IsAlive executes every 60 seconds and determines whether the server responds properly, based on the results returned by the stored procedure.

How SQL Server clusters are detected online