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The SQL Server Resource Governor is a feature that enables you to manage SQL Server workload and system resource consumption. Its primary function is resource allocation and isolation. This tool is especially beneficial in a multi-tenant environment where multiple applications are competing for resources. It helps system administrators to classify incoming workloads, and to set resource limits and priorities for these workloads.

To utilize the SQL Server Resource Governor, you need to create resource pools and workload groups. Resource pools represent a subset of physical resources available to SQL Server, while workload groups are used for grouping similar sessions together and routing them to the appropriate resource pool. This is done using the CREATE RESOURCE POOL and CREATE WORKLOAD GROUP commands.

-- Creating a resource pool in SQL Server
CREATE RESOURCE POOL FastPool 
WITH
(
  MAX_CPU_PERCENT = 70,
  MIN_CPU_PERCENT = 50,
  MAX_MEMORY_PERCENT = 60,
  MIN_MEMORY_PERCENT = 40
);

-- Creating a workload group
CREATE WORKLOAD GROUP FastGroup
USING FastPool;

Once you have created your resource pools and workload groups, you need to classify incoming requests. This is done using a classifier function, which is a user-defined function that returns the name of the workload group where the new session should be placed. You can create a classifier function using the CREATE FUNCTION command.

-- Creating a classifier function in SQL Server
CREATE FUNCTION dbo.ClassifierFunction() 
RETURNS SYSNAME 
WITH SCHEMABINDING 
AS 
BEGIN 
  IF (ORIGINAL_LOGIN()= 'FastUser') 
    RETURN 'FastGroup';
  RETURN 'Default'; 
END;

In Azure SQL and Azure Synapse, workload management and isolation can be achieved through similar mechanisms. For Azure SQL, Elastic Pools provide a simple and cost-effective solution to manage and scale multiple databases that have varying and unpredictable usage demands. In Azure Synapse, workload management is done using workload groups and workload importance, similar to SQL Server Resource Governor.

MySQL and DB2, however, do not have a direct equivalent to the SQL Server Resource Governor. In MySQL, you can use the MAX_USER_CONNECTIONS variable to limit the number of simultaneous connections for a given user, which can help to manage resources. DB2 provides workload management features through the use of workload manager database partitions and service subclasses.

In conclusion, SQL Server Resource Governor is a powerful tool for workload management and isolation. While the principles of workload management are similar across different database systems, the specific implementation and features can vary. Regardless of the system you are using, understanding and effectively managing your workloads is key to ensuring optimal performance and resource usage.