TiCDC cluster-id prefix collision causes changefeeds from another cluster to be loaded after restart

[lidezhu]

What did you do?

When two TiCDC clusters use cluster-id values with a prefix relationship (e.g., new-arch-for-fs and new-arch-for-fs-index) and share the same PD/etcd, a changefeed created in one cluster becomes visible in the other cluster after it restarts. This occurs because etcd keys are scanned by prefix (/tidb/cdc/<cluster-id>) without a path-segment boundary, so /tidb/ cdc/new-arch-for-fs also matches /tidb/cdc/new-arch-for-fs-index.

1. Deploy two TiCDC servers on the same PD/etcd:

- cdc-8505 with --cluster-id new-arch-for-fs-index 
- cdc-8510 with --cluster-id new-arch-for-fs 

2. Confirm initial changefeeds:

tiup cdc:v8.5.4 cli changefeed list --server http://10.2.4.11:8505 
tiup cdc:v8.5.4 cli changefeed list --server http://10.2.4.11:8510

3. Create a changefeed on the new-arch-for-fs-index cluster:

tiup cdc:v8.5.4 cli changefeed create \ 
  --server http://10.2.4.11:8505 \ 
  --changefeed-id prefix-collision-test \ 
  --sink-uri blackhole:// 

4. Verify it appears only on new-arch-for-fs-index:

tiup cdc:v8.5.4 cli changefeed list --server http://10.2.4.11:8505 

5. Restart the new-arch-for-fs TiCDC server:

tiup cluster restart ds-test -R cdc --node 10.2.4.11:8510 -y 

5. After restart, list changefeeds on new-arch-for-fs:

tiup cdc:v8.5.4 cli changefeed list --server http://10.2.4.11:8510 

Observed: prefix-collision-test now appears in new-arch-for-fs cluster.

What did you expect to see?

Changefeeds created under new-arch-for-fs-index should never appear in new-arch-for-fs.

What did you see instead?

After restarting new-arch-for-fs, it loads the changefeed created under new-arch-for-fs-index.

Versions of the cluster

Upstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

(paste TiDB cluster version here)

Upstream TiKV version (execute tikv-server --version):

(paste TiKV version here)

TiCDC version (execute cdc version):

(paste TiCDC version here)