How to clear the database connection of sleep

There are many connections in the database that have been continuously sleeping, which are issued by the metabase application database and the data source databases.
We tried to kill these connections, but they will be created again soon,
May I ask if there is any way to clear these connections?

Diagnostic Info:
"browser-info": {
"language": "ja",
"platform": "Win32",
"userAgent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/ Safari/537.36",
"vendor": "Google Inc."
"system-info": {
"file.encoding": "UTF-8",
"": "OpenJDK Runtime Environment",
"java.runtime.version": "11.0.19+7-LTS",
"java.vendor": " Inc.",
"java.vendor.url": "OpenJDK Download - Corretto - AWS",
"java.version": "11.0.19",
"": "OpenJDK 64-Bit Server VM",
"java.vm.version": "11.0.19+7-LTS",
"": "Linux",
"os.version": "5.10.215-203.850.amzn2.x86_64",
"user.language": "en",
"user.timezone": "Japan"
"metabase-info": {
"databases": [
"hosting-env": "unknown",
"application-database": "mysql",
"application-database-details": {
"database": {
"name": "MySQL",
"version": "8.0.26"
"jdbc-driver": {
"name": "MariaDB Connector/J",
"version": "2.7.6"
"run-mode": "prod",
"version": {
"date": "?",
"tag": "vUNKNOWN",
"branch": "?",
"hash": "?"
"settings": {
"report-timezone": null

What version are you running since the tag says UNKNOWN.

There is an env variable that you can change which will get rid of idle connections after 20 min ... But this is available Since: v47.4



](Environment variables)

Are you referring to this environment variable?
But I see that the description of this variable is specific to the connection of the datasource databases.
Does the connection to the metabase application also have an effect?
Because we now see that the number of connections in the metabase application database has been consistently high and cannot be killed.