mysql server slowly eats memories when using InnoDB Cluster

[takumi koba]

We have set up a group replication with three servers using a single-primary mode. Right after the cluster was established, each MySQL Server was utilizing approximately 500MB of memory. However, upon checking one week later, it was observed that all servers were using around 2.6GB of memory each. No significant data inserts were performed during this one-week period. Currently, it seems that the increase in memory usage by the MySQL Server has come to a halt.

We would like to understand whether this phenomenon is normal when using InnoDB Cluster. Additionally, if it is normal, we are interested in knowing how the memory is being allocated.

The performance specifications of the servers in use are as follows:
===========================
OS:Ubuntu 20.04.6 LTS
Memory:4GB
mysql Ver 8.0.35-0ubuntu0.20.04.1 for Linux on x86_64 ((Ubuntu))
===========================

This is the result of executing systemctl status mysql.
===========================
systemctl status mysql

● mysql.service - MySQL Community Server
Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2023-11-20 17:07:35 JST; 1 weeks 1 days ago
Main PID: 220333 (mysqld)
Status: "Server is operational"
Tasks: 57 (limit: 4625)
Memory: 2.6G
CGroup: /system.slice/mysql.service
└─220333 /usr/sbin/mysqld
===========================

Please give us some advice.