Hi @bitone,
You can install the 8.4 client. You just need any MySQL client to be able to connect to the admin interface of ProxySQL. With percona-release use the enable subcommand rather than setup.
In this context I have another question: I wrote some mysql client (in C) using libmysql.
RHEL 9 offers me mariadb-connector-c-devel, but there seems to be some issue with this library connecting to ProxySQL when using prepared statements with RO cursors…
What Percona repository and package can I install to get libmysql and the developer files?
You can get percona-server-devel package which has the libmysqlclient library, and other developer files.
I’d also advise against prepare statements unless you are executing the same SELECT query many thousands of times with just a parameter change. Using prepared statements for every SELECT is huge overhead. If you have many select-and-done queries, just send the query.