Region health high learner count

[sykp241095]

Original author: Ciprian_B
Original time: 2024-03-14 10:58:58.4109
Original ID/Slug: 804 / region-health-high-learner-count

Application environment:

Three-Node Hybrid Deployment

TiDB version:

7.5

Problem:

Not sure if it is a problem , but the learner-peer-region-count is not 0 and does not seem to be decresing.

I do not seem to find any info for learner-peer-region-count

[sykp241095]

Original author: hello-wxz
Original time: 2024-03-14 13:33:12.207715

In your case, if the learner-peer-region-count is not decreasing, it may indicate that there are regions in your TiDB cluster where the learner peers are not being promoted to full members or are not being removed as expected. This situation can potentially impact the overall health and performance of the cluster. To troubleshoot and address this issue, you can consider the following steps:

1. Check the configuration and placement rules to ensure that learner peers are being utilized correctly. You can use the config placement-rules show command to view the placement rules .

2. Verify the regions that have learner peers using the region command with the appropriate filters to identify regions with learner peers that are not transitioning as expected .

3. Monitor the cluster using TiKV-Details to observe any leader transfers and ensure that learner nodes are migrating their leaders properly .

4. If there are still lingering learner peers that have not transitioned, you can refer to specific commands or procedures to facilitate the conversion of voter peers to learner peers .

By following these steps and closely monitoring the cluster, you can address the high learner count and ensure the proper functioning of your TiDB deployment.

[sykp241095]

Original author: TiDB-AI-Assistant
Original time: 2024-03-14 13:33:18.95984

Sorry, I have no idea about it, let’s try another question.

[sykp241095]

Original author: Ciprian_B
Original time: 2024-03-14 14:10:46.088432

Thanks for the detailed answer @hello-wxz

Can this happen because i added for testing only a tiflash instance ?

[sykp241095]

Original author: Mini256
Original time: 2024-03-22 08:21:17.369866

This may be related to TiFlash, because Tiflash always replicates asynchronous as the leaner role in Raft Layer, so you will find a certain amount of learner-peer-region-count after creating a Tiflash replica.

Check the post to learn more about it: Please tell me why the extra-peer-region-count is very high and will not decrease, and then start_key is empty. (Translate Version)