slow kafka sink when upstream write data

[wk989898]

What did you do?

1. start a changefeed with kafka sink
2. write some data (100mb/s)
3. stop writing the data

What did you expect to see?

No response

What did you see instead?

After stopping to write data, the sink write bytes increase

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):

release-8.5