Lesson Learned #410:Custom CPU Management in Azure SQL DB: Implementing a Pseudo-Resource Governor

[Jose_Manuel_Jurado]

Azure SQL Database is a powerful platform that provides managed database services with built-in intelligence and robust resource management. While Azure SQL Database doesn't have a direct implementation of the traditional Resource Governor feature available in SQL Server, we can explore a pseudo-Resource Governor approach using user-defined functions and custom tables. In this article, we'll discuss the concept, present a sample implementation using a custom function, and highlight the possibilities it opens up for controlling CPU resources in Azure SQL Database.

Understanding the Concept:

The Resource Governor in SQL Server allows you to manage system resource consumption by classifying workloads and assigning resource limits to each workload group. While this feature is not directly available in Azure SQL Database, we can create a pseudo-Resource Governor using a combination of user-defined functions and custom configuration tables. This approach allows us to control CPU resources for specific users or workloads within the database, ensuring efficient resource allocation and preventing resource contention.

Sample Implementation using User-Defined Function:

Let's demonstrate the pseudo-Resource Governor concept with a sample implementation using a user-defined function. In this example, we'll create a function named `dbo.GetMaxDopByUsername`, which fetches the Maximum Degree of Parallelism (MAXDOP) setting for a given user from a custom configuration table. If the user-specific MAXDOP is not defined, the function will fall back to a default value obtained from the system configuration.

CREATE OR ALTER FUNCTION dbo.GetMaxDopByUsername
(
    @username sysname = 'all'
)
RETURNS INT
AS
BEGIN
    DECLARE @maxDop INT = null

    IF (@username IS NULL)
        SET @username = USER_NAME();

    -- If @username is 'all', use the configuration from the table
    IF (TRIM(LOWER(@username)) = 'all')
    BEGIN
        SELECT @MaxDop = COALESCE(CONVERT(INT, value), 0)
        FROM SYS.database_scoped_configurations
        WHERE name = 'MAXDOP';
    END
    ELSE
    BEGIN
        -- Search for the MAXDOP for the specific user in the table
        SELECT @maxDop = COALESCE(MaxDop, 0)
        FROM dbo.UserResourceGovernorConfig
        WHERE UserName = @username;

        -- If the user does not have a configured MAXDOP, use the configuration from the table for 'all'
        IF (@maxDop IS NULL)
        BEGIN
            SELECT @MaxDop = COALESCE(CONVERT(INT, value), 0)
            FROM SYS.database_scoped_configurations
            WHERE name = 'MAXDOP';
        END
    END

    RETURN @maxDop;
END;

Custom Configuration Table:

To manage the CPU limits for specific users or workloads, we'll create a custom table named `dbo.UserResourceGovernorConfig`. This table will store the MAXDOP settings for individual users and allows for a fine-grained control over CPU resources.

CREATE TABLE dbo.UserResourceGovernorConfig (
    UserName sysname PRIMARY KEY,
    MaxDop INT
);
INSERT INTO dbo.UserResourceGovernorConfig (UserName, MaxDop)
VALUES ('dbo', 4),
       ('usuario2', 2);

Benefits and Possibilities:

1. Custom CPU Management: The pseudo-Resource Governor approach enables us to tailor CPU resource allocation for specific users or workloads, ensuring optimal performance for critical tasks.

2. Preventing Resource Contention: By setting CPU limits, we can prevent resource contention and prioritize critical queries, avoiding performance bottlenecks.

3. Flexibility and Control: With the custom configuration table, we can easily adjust CPU limits as workload demands change, providing flexibility and better control over resource usage.

Example:

select 'SELECT * FROM PerformanceVarcharnVarhcar ORDER BY NEWID() OPTION (MAXDOP ' + CONVERT(varchar(10),dbo.GetMaxDopByUsername('DBO')) + ')'

Conclusion:

While Azure SQL Database doesn't offer a direct Resource Governor feature, we can implement a pseudo-Resource Governor using user-defined functions and custom tables.

This approach allows us to control CPU resources and optimize performance for specific users or workloads within the database. By leveraging this custom solution, Azure SQL Database users can enjoy more efficient resource allocation and ensure a smooth and responsive database experience.

Remember to carefully manage and monitor your resource allocations to achieve optimal performance, and explore the possibilities of fine-tuning your Azure SQL Database to match your specific workload requirements.

Enjoy!