Changefeed got stuck due to can not finish incremental scan when many tables share one region.

[asddongmen]

After creating 10 million empty tables, PD will merge them into only more than 1,000 regions, so that many tables share one region.
Moreover, these regions are located on a small number of TiKV nodes, which will cause the cdc incremental scan to fully utilize the CPU of the TiKV endpoint, and the incremental scan cannot be completed. Which lead to changefeed got stuck.

CDC Version

Release Version: v9.0.0-alpha-185-gb3c5be2a
Git Commit Hash: b3c5be2a5565c111a4babfe10b5b7f3bfb87da74
Git Branch: master
UTC Build Time: 2025-03-27 03:10:59
Go Version: go version go1.23.4 darwin/arm64
Failpoint Build: false

TiKV Version

v8.5.1

[asddongmen]

• Even when I imported 15TB of data and increased the number of regions to 60,000, the problem still persisted.
• Finally, by reducing the region size to 24MB, the regions were split to 600,000, and the problem was solved. Calculated, there are only 16 tables on average in each region, so that the incremental scan will not fail to complete.