Flink 1.6, increment Checkpoint, the shared dir stored the last year checkpoint state

[LakeShen]

Hi community，
        now I have a flink sql job, and I set the flink sql sate retention
time, there are three dir in flink checkpoint dir :
1. chk -xx dir
2. shared dir
3. taskowned dir

I find the shared dir store the last year checkpoint state,the only reason
I thought is that the latest
checkpoint retain reference of last year checkpoint state file.
Are there any other reason to lead this? Or is it a bug?

Thanks to your replay.

Best wishes,
Lake Shen