How does ClickHouse Resource Governor work?

Introduction

ClickHouse Resource Governor is a feature that allows DBAs to allocate system resources, such as CPU, memory, and I/O operations, to specific users or groups of users. The Resource Governor provides a way to prioritize and allocate resources to ensure that critical queries and users have access to the necessary resources.

Here’s how ClickHouse Resource Governor works:

  1. Configuration: The Resource Governor is configured by setting parameters in the config.xml file. These parameters include max_threads, which sets the maximum number of threads that can be used by each user or group, and max_memory_usage, which sets the maximum amount of memory that can be used by each user or group.
  2. Resource Group Membership: Users are assigned to specific Resource Groups based on their roles, login names, or other criteria. Each user can be a member of only one Resource Group at a time.
  3. Resource Allocation: Resources are allocated based on the defined parameters once the Resource Groups are defined. This includes CPU time, memory, and I/O operations. The Resource Governor manages these resources dynamically based on the current load on the system.
  4. Resource Limit Enforcement: The Resource Governor enforces the resource limits for each group, ensuring that critical queries and users have access to the necessary resources. If a group exceeds its resource limits, the Resource Governor will limit the resources available to that group, preventing it from negatively impacting the performance of other groups.
  5. Monitoring: The Resource Governor provides monitoring tools to track resource usage for each group. This includes system views that show the current resource usage and alerts that can be configured to notify administrators when a group exceeds its resource limits.

By implementing the ClickHouse Resource Governor, DBAs can allocate resources based on the needs of the database and ensure that critical queries and users have access to the necessary resources. This can help to improve the overall performance and stability of the database.

SQL to monitor ClickHouse Resource Governor

To monitor the ClickHouse Resource Governor, you can use the following SQL queries:

  1. To view all defined resource groups:
SELECT * FROM system.query_log WHERE type = 'ResourceLimits';

This query will return a list of all defined resource groups, including their names, CPU limits, and memory limits.

  1. To view the current status of the Resource Governor:
SELECT * FROM system.query_log WHERE type = 'ResourceLimitsExceeded';

This query will return the current status of the Resource Governor, including the number of queries affected by resource constraints and the number of queries killed due to exceeding resource limits.

  1. To view the resource usage by each resource group:
SELECT * FROM system.runtime_limits;

This query will return the resource usage by each resource group, including CPU time, memory usage, and I/O operations.

  1. To view the active queries for a specific resource group:
SELECT * FROM system.processes WHERE user_name = 'resource_group_name';

This query will return the active queries for a specific resource group, where resource_group_name is the name of the resource group.

Conclusion

By using these queries, DBAs can monitor the ClickHouse Resource Governor and identify any performance issues related to resource allocation. They can also use this information to make adjustments 

To read more about ClickHouse internals, do consider reading the below articles

About Shiv Iyer 215 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.