background encryption threads consuming a lot of CPU after background re-encryption for new key version finished

how to reproduce:

• create data-at-rest encryption setup with hashicorp key mgmt plugin
• create a key on the hashicorp vault side
• create a table and encrypty it using the generated key
• create two new key versions on the vault server (two are needed at minimum for background key encoding to kick in)

while re-encryption is ongoing the mariadbd process takes about 10-15% CPU in my test setup

after re-encryption is complete the mariadbd process still shows CPU usage fluctuating between 10-30% even though the server should be completely idle, and in per-thread view in "top" it is clear that it is the background encryption threads that consume the CPU time

then changing hashicorp_key_management_cache_version_timeout from its default 0 to 100 milliseconds the CPU usage goes up to some 100 to 130%.

my config settings:

[mysqld]

performance_schema=ON

plugin_load_add = hashicorp_key_management.so

hashicorp-key-management

hashicorp-key-management-vault-url="..."

hashicorp-key-management-token="...."

innodb_encrypt_tables = FORCE

innodb_encrypt_log = ON

innodb_encrypt_temporary_tables = ON

innodb_encryption_threads = 4

innodb_encryption_rotate_key_age = 1

innodb_default_encryption_key_id = 1

innodb_encryption_rotation_iops=100

aria_encrypt_tables = ON

encrypt_tmp_disk_tables = ON

encrypt_tmp_files = ON

log-bin

encrypt_binlog = ON