Optimize the reconciliation loop

Oct 13, 2025 by miodeya.com 34 views

Introduction

In this article, we will explore the issue of the tidb Service resource being constantly updated in a Kubernetes cluster. This behavior is observed in a specific scenario where the TiDB Operator is managing the tidb Service resource. We will delve into the details of the issue, analyze the logs, and discuss possible solutions to optimize the behavior of the TiDB Operator.

Background

The TiDB Operator is a Kubernetes operator that manages TiDB clusters. It provides a way to deploy, manage, and scale TiDB clusters in a Kubernetes environment. The operator is responsible for creating and managing the necessary resources, including Services, to enable communication between the TiDB pods and the outside world.

The Issue

In this scenario, we observe that the tidb Service resource is being constantly updated. This is evident from the debug logs, which show repeated calls to the secondaryToPrimaryMapper function. The logs indicate that the Service resource is being updated every few seconds, with the resourceVersion attribute changing each time.

2025-03-10 20:20:30,167 DEBUG [si.pel.nod.ope.DnsZoneReconciler] (-2048888303-pool-8-thread-2) secondaryToPrimaryMapper: Service{tidb-dev/dev-tidb} -> DnsZone{}
2025-03-10 20:20:30,173 DEBUG [si.pel.nod.ope.DnsZoneReconciler] (-2048888303-pool-8-thread-4) secondaryToPrimaryMapper: Service{tidb-dev/dev-tidb} -> DnsZone{}
...

Analysis

To further investigate the issue, we use kubectl to retrieve the Service resource and examine its metadata. We notice that the resourceVersion attribute is changing each time we retrieve the resource.

peter@pad:~$ date; kubectl -n tidb-infra get Service infra-tidb -o yaml | yq .metadata.resourceVersion
Mon Mar 10 09:24:42 PM CET 2025
252137056
peter@pad:~$ date; kubectl -n tidb-infra get Service infra-tidb -o yaml | yq .metadata.resourceVersion
Mon Mar 10 09:24:59 PM CET 2025
252137256

We also use diff to compare the two Service resources, and we notice that the only difference is in the resourceVersion attribute.

peter@pad:~$ kubectl -n tidb-infra get Service infra-tidb -o yaml > tidb-infra-service.1.yaml 
peter@pad:~$ kubectl -n tidb-infra get Service infra-tidb -o yaml > tidb-infra-service.2.yaml 
peter@pad:~$ diff -c tidb-infra-service.1.yaml tidb-infra-service.2.yaml 
*** tidb-infra-service.1.yaml   2025-03-10 21:26:25.892254353 +0100
--- tidb-infra-service.2.yaml   2025-03-10 21:26:56.222241483 +0100
***************
*** 20,26 ****
      kind: TidbCluster
      name: infra
      uid: dda0e131-56fb-41fb-909f-86f99a676e7f
!   resourceVersion: "252137633"
    uid: 82fd6c12-064a-4dbb-9e07-d875de89ff02
  spec:
    allocateLoadBalancerNodePorts: true
--- 20,26 ----
      kind: TidbCluster
      name: infra
      uid: dda0e131-56fb-41fb-909f-86f99a676e7f
!   resourceVersion: "252137817"
    uid: 82fd6c12-064a-4dbb-9e07-d875de89ff02
  spec:
    allocateLoadBalancerNodePorts: true

Possible Solutions

Based on our analysis, we can identify a few possible solutions to optimize the behavior of the TiDB Operator:

Optimize the reconciliation loop: The reconciliation loop is responsible for updating the Service resource. We can optimize the loop to reduce the frequency of updates or to only update the resource when necessary.
Use a more efficient update mechanism: Instead of using the secondaryToPrimaryMapper function, we can use a more efficient update mechanism, such as a cache or a queue, to reduce the number of updates.
Disable unnecessary updates: We can disable unnecessary updates by setting the resourceVersion attribute to a fixed value or by using a different attribute to track changes.

Conclusion

In this article, we explored the issue of the tidb Service resource being constantly updated in a Kubernetes cluster. We analyzed the logs, examined the metadata, and identified possible solutions to optimize the behavior of the TiDB Operator. By optimizing the reconciliation loop, using a more efficient update mechanism, or disabling unnecessary updates, we can reduce the frequency of updates and improve the performance of the TiDB Operator.

Recommendations

Based on our analysis, we recommend the following:

Optimize the reconciliation loop: The reconciliation loop is responsible for updating the Service resource. We can optimize the loop to reduce the frequency of updates or to only update the resource when necessary.
Use a more efficient update mechanism: Instead of using the secondaryToPrimaryMapper function, we can use a more efficient update mechanism, such as a cache or a queue, to reduce the number of updates.
Disable unnecessary updates: We can disable unnecessary updates by setting the resourceVersion attribute to a fixed value or by using a different attribute to track changes.

By implementing these recommendations, we can improve the performance of the TiDB Operator and reduce the frequency of updates to the tidb Service resource.

Introduction

In our previous article, we explored the issue of the tidb Service resource being constantly updated in a Kubernetes cluster. We analyzed the logs, examined the metadata, and identified possible solutions to optimize the behavior of the TiDB Operator. In this article, we will provide a Q&A section to address some of the common questions related to this issue.

Q: What is the cause of the constant updates to the `tidb` Service resource?

A: The constant updates to the tidb Service resource are caused by the reconciliation loop in the TiDB Operator. The reconciliation loop is responsible for updating the Service resource to ensure that it is in sync with the actual state of the TiDB cluster.

Q: Why is the reconciliation loop updating the Service resource so frequently?

A: The reconciliation loop is updating the Service resource frequently because it is designed to be highly available and fault-tolerant. The loop is constantly monitoring the state of the TiDB cluster and updating the Service resource accordingly.

Q: Can I disable the reconciliation loop to prevent the constant updates?

A: Yes, you can disable the reconciliation loop to prevent the constant updates. However, this may impact the availability and fault-tolerance of the TiDB Operator.

Q: What are some possible solutions to optimize the behavior of the TiDB Operator?

A: Some possible solutions to optimize the behavior of the TiDB Operator include:

Optimizing the reconciliation loop: The reconciliation loop can be optimized to reduce the frequency of updates or to only update the resource when necessary.
Using a more efficient update mechanism: Instead of using the secondaryToPrimaryMapper function, a more efficient update mechanism, such as a cache or a queue, can be used to reduce the number of updates.
Disabling unnecessary updates: Unnecessary updates can be disabled by setting the resourceVersion attribute to a fixed value or by using a different attribute to track changes.

Q: How can I monitor the behavior of the TiDB Operator?

A: You can monitor the behavior of the TiDB Operator by using tools such as kubectl and kubectls. You can also use logging and monitoring tools to track the behavior of the operator.

Q: What are some best practices for deploying and managing TiDB clusters in Kubernetes?

A: Some best practices for deploying and managing TiDB clusters in Kubernetes include:

Using a consistent naming convention: A consistent naming convention should be used for all resources, including pods, services, and persistent volumes.
Using labels and annotations: Labels and annotations can be used to organize and categorize resources.
Using a configuration management tool: A configuration management tool, such as Ansible or Terraform, can be used to manage the configuration of the TiDB cluster.
Using a monitoring and logging tool: A monitoring and logging tool, such as Prometheus or Grafana, can be used to monitor and log the behavior of the TiDB cluster.

Conclusion

In this article, we provided a Q&A section to address some of the common questions related to the issue of the tidb Service resource being constantly updated in a Kubernetes cluster. We also provided some best practices for deploying and managing TiDB clusters in Kubernetes. By following these best practices and optimizing the behavior of the TiDB Operator, you can improve the performance and availability of your TiDB cluster.

Recommendations

Based on our analysis, we recommend the following:

Optimize the reconciliation loop: The reconciliation loop can be optimized to reduce the frequency of updates or to only update the resource when necessary.
Use a more efficient update mechanism: Instead of using the secondaryToPrimaryMapper function, a more efficient update mechanism, such as a cache or a queue, can be used to reduce the number of updates.
Disable unnecessary updates: Unnecessary updates can be disabled by setting the resourceVersion attribute to a fixed value or by using a different attribute to track changes.

By implementing these recommendations, you can improve the performance and availability of your TiDB cluster.