s3 sink: table directory become an object.

[dengqee]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.
   I created a Changefeed for S3 Sink for a TIDB cluster that already had some tables. And I insert some data into an existing table.
2. What did you expect to see?
   S3 server create a t_60 directory, and there is a cdclog.xxxxxxxx inside t_60.
3. What did you see instead?
   S3 server created a t_60 object with the size of 0 bytes.
   
   changefeed error:

"code": "CDC:ErrProcessorUnknown",
"message": "[CDC:ErrS3SinkStorageAPI]XMinioParentIsObject: Object-prefix is already an object, please choose a different object-prefix name.\n\tstatus code: 400, request id: 166825DDCC17A799, host id: "

4. Versions of the cluster

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

     | Release Version: v4.0.10
     Edition: Community
     Git Commit Hash: dbade8cda4c5a329037746e171449e0a1dfdb8b3
     Git Branch: heads/refs/tags/v4.0.10
     UTC Build Time: 2021-01-15 02:59:27
     GoVersion: go1.13
     Race Enabled: false
     TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
     Check Table Before Drop: false |
     

   • TiCDC version (execute cdc version):

     Release Version: v4.0.10
     Git Commit Hash: bced60a8d65f31ab68a35f1f309ea2345076096c
     Git Branch: heads/refs/tags/v4.0.10
     UTC Build Time: 2021-01-14 12:38:40
     Go Version: go version go1.13 linux/amd64