Why etcd dbsize_in_use decrease after restart?

[javapracticer]

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"

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.

Etcd version: v3.5.2

[ahrtr]

To double confirm, do you mean etcd_mvcc_db_total_size_in_bytes kept increasing slightly every 5 minutes, while etcd_mvcc_db_total_size_in_use_in_bytes kept unchanged and reduced by half after restarting the etcdserver?

Etcd version: v3.5.2

Can you try the latest patch 3.5.22 or 3.6.4?

[serathius]

Have you set bootstrap-defrag-threshold-megabytes command line flag?