Greenplum Resource Queues: Managing Workloads

Resource queues in Greenplum are a critical component for managing workloads efficiently and ensuring that system resources are allocated appropriately to different user groups or query types. Resource queues help prioritize and control the execution of queries based on their importance and resource requirements. Here's a guide on managing workloads using Greenplum resource queues:

 1. Introduction to Resource Queues:

   - Definition:

     - Resource queues in Greenplum are used to allocate system resources, such as CPU, memory, and I/O, among different workloads or user groups.

   - Purpose:

     - Prioritize and control the execution of queries to ensure fair resource distribution.

 2. Creating Resource Queues:

   - Syntax:

     

     CREATE RESOURCE QUEUE queue_name [WITH (property_name = value, ...)];

     

   - Example:

     

     CREATE RESOURCE QUEUE high_priority WITH (ACTIVE_STATEMENTS=5, MEMORY_LIMIT='1GB');

     

 3. Assigning Users to Resource Queues:

   - Syntax:

     

     ALTER ROLE username RESOURCE QUEUE queue_name;

     

   - Example:

     

     ALTER ROLE analyst_user RESOURCE QUEUE high_priority;

     

 4. Automatic Queue Assignment with Rules:

   - Rule-Based Assignment:

     - Use rules to automatically assign queries to specific resource queues based on criteria like username, group, or query attributes.

   - Example:

     

     CREATE RESOURCE QUEUE_RULE high_priority_rule WITH (ROLE='analyst_user') TO high_priority;

     

 5. Manually Assigning Queries to Queues:

   - ALTER SYSTEM Statement:

     - Users with appropriate privileges can manually assign queries to specific resource queues using the `ALTER SYSTEM` statement.

   - Example:

     

     ALTER SYSTEM SET RESOURCE_QUEUE = 'high_priority' FOR SESSION;

     

 6. Priority Scheduling:

   - Definition:

     - Resource queues can have different priority levels, allowing high-priority queues to receive more resources during contention.

   - Example:

     

     ALTER RESOURCE QUEUE high_priority WITH (PRIORITY=HIGH);

     

 7. Configuring Resource Limits:

   - Memory Limit:

     - Set memory limits for resource queues to ensure fair resource allocation.

   - Example:

     

     ALTER RESOURCE QUEUE high_priority WITH (MEMORY_LIMIT='2GB');

     

 8. Monitoring Resource Queues:

   - Greenplum Command Center (GPCC):

     - Use GPCC to monitor resource usage, query performance, and workload distribution across resource queues.

   - Query Monitoring Views:

     - Utilize system views like `pg_stat_activity` to monitor the current query activity in different queues.

 9. Controlling Maximum Concurrent Statements:

   - Definition:

     - Control the number of queries that can run simultaneously in a resource queue.

   - Example:

     

     ALTER RESOURCE QUEUE low_priority WITH (MAX_COST=500, MAX_MEMORY=1GB, MAX_DISK=1GB);

     

 10. Adjusting Resource Queue Properties Dynamically:

    - gpconfig Utility:

      - Dynamically change configuration parameters for resource queues using the `gpconfig` utility.

    - Example:

      

      gpconfig -c max_statement_mem -v 2GB -m on

      

 11. Setting Resource Limits for Groups of Queries:

    - Query Groups:

      - Group queries together and apply resource limits to the entire group for collective management.

    - Example:

      

      CREATE RESOURCE QUEUE_GROUP data_loaders WITH (MEMORY_LIMIT='5GB');

      ALTER RESOURCE QUEUE_GROUP data_loaders ADD QUEUE low_priority;

      

 12. Integration with External Workload Managers:

    - Connectors:

      - Greenplum can integrate with external workload managers, allowing seamless interaction with scheduling tools like Apache Airflow or Kubernetes.

    - Example:

      

      CREATE RESOURCE QUEUE my_queue WITH (CONCURRENCY=5, MEMORY_LIMIT='2GB') WITH (SERVICE_NAME='my_service');

      

 13. Backup and Restore Resource Queue Configurations:

    - Backup Statements:

      - Back up resource queue definitions and configurations to quickly restore configurations in case of issues.

    - Example:

      

      ALTER RESOURCE QUEUE high_priority WITH (MAX_MEMORY=3GB);

      ALTER RESOURCE QUEUE medium_priority WITH (MAX_MEMORY=2GB);

      -- Backup statements

      SELECT * FROM pg_resourcequeue;

      

 14. Query Prioritization with Resource Pools:

    - Definition:

      - Resource pools allow for additional control over resource allocation by grouping multiple queues together.

    - Example:

      

      CREATE RESOURCE POOL analytics_pool WITH (CPU_RATE_LIMIT='50%', MEMORY_LIMIT='10GB');

      ALTER RESOURCE QUEUE low_priority SET RESOURCE POOL = analytics_pool;

      

 15. Upgrade Considerations:

    - Workload Management Considerations:

      - Review workload management considerations when planning Greenplum upgrades to ensure compatibility.

 16. Logging and Auditing:

    - Enable Query Logging:

      - Enable query logging to capture detailed information about queries, including resource usage.

    - Example:

      

      ALTER RESOURCE QUEUE high_priority WITH (MAX_MEMORY=3GB);

      

 17. Documentation:

    - Document Resource Queue Configurations:

      - Maintain comprehensive documentation on resource queue configurations and procedures for managing workloads.

Resource queues provide a powerful mechanism for managing workloads in Greenplum, allowing administrators to prioritize and allocate resources based on the importance of queries or user groups. Regular monitoring, tuning, and adjustments based on changing workload characteristics are essential for effective workload management.