etcd dbsize_in_use decrease after restart

[javapracticer]

Bug report criteria

• This bug report is not security related, security issues should be disclosed privately via security@etcd.io.
• This is not a support request or question, support requests or questions should be raised in the etcd discussion forums.
• You have read the etcd bug reporting guidelines.
• Existing open issues along with etcd frequently asked questions have been checked and this is not a duplicate.

What happened?

When the dbsize_in_use of my etcd is 2GB smaller than the dbsize, the dbsize increases slightly every five minutes. After I restarted etcd, the dbsize_in_use was immediately reduced by half, and the db_size stopped growing.
My auto-compaction strategy is set as follows:
auto-compaction-retention = "5m"

What did you expect to happen?

I want to know why the dbsize keeps increasing, and why the etcd db_size_in_use is immediately reduced by half after a restart. This is very confusing to me.

How can we reproduce it (as minimally and precisely as possible)?

i don't know

Anything else we need to know?

No response

Etcd version (please run commands below)

v3.5.2

Etcd configuration (command line flags or environment variables)

Details

paste your configuration here

Etcd debug information (please run commands below, feel free to obfuscate the IP address or FQDN in the output)

Details

$ etcdctl member list -w table
# paste output here

$ etcdctl --endpoints=<member list> endpoint status -w table
# paste output here

Relevant log output