What could be the reasons for a sudden decrease in regions?

This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: region突然变少可能是哪些原因导致

| username: TiDBer_pkQ5q1l0

To improve efficiency, please provide the following information. Clear problem descriptions can be resolved more quickly:
【TiDB Usage Environment】Testing
【TiDB Version】v5.2.1
【Encountered Problem】
The number of regions suddenly increased and then decreased. There was no new data added or deleted in the business. What could be the reason for this?
【Reproduction Path】What operations were performed that caused the problem
【Problem Phenomenon and Impact】

| username: xfworld | Original post link

If the ability to enable region merging is available, regions that meet the merging conditions will be merged to reduce system overhead and improve performance.

You can check the empty regions…

| username: cheng | Original post link

He said there is no new data, so shouldn’t the number of regions decrease after merging? Why is there an increase in the number of regions?

| username: TiDBer_jYQINSnf | Original post link

Take a look at the operator column in PD; all operations related to regions are recorded there. It’s very clear.

| username: h5n1 | Original post link

  1. Are you sure there are no data additions or deletions?
  2. Are there any DDL operations like creating tables, where each partition would have a region?
  3. Is the query quite busy? There is a Load base split, but if the region query exceeds the split.qps-threshold (QPS threshold of 30000) and split.byte-threshold of 30M/s within 10 seconds, it will cause the region to split.
  4. Is there any manual split?
  5. Check the PD monitoring page to see what operators were active during that time period.
| username: TiDBer_pkQ5q1l0 | Original post link

During the business stress test, many empty regions were created on PD, and after the stress test ended, these empty regions merged again.

| username: system | Original post link

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