Slow query log first. A larger buffer pool is not the opening move.
Oracle MySQL, already running. InnoDB buffer pool against the RAM you have, a query that holds the threads, an auth plugin that is not a performance problem. If the binary is mariadbd, use the MariaDB page.
Threads, the buffer pool, one statement
Turned on long enough to catch the statement, then off. An index is added only on a table the application owns. A paid plugin query is reported, not rewritten.
Sized to the data that fits, not to a blog default of 70% on a 2 GB VPS that also runs PHP. Too large and the kernel kills mysqld.
max_connections above the PHP-FPM pool does nothing. Below it, the site errors while MySQL looks idle. We match them.
MySQL down is support. A version jump is a migration.
Tuning assumes the server accepts connections. A conversion to MariaDB is not a performance fix.
€55 an hour. The first hour is the slow log.
Minimum 1 hour. If the log is empty and the buffer pool is not thrashing, we stop. There is nothing to tune.
MySQL the busy process, site otherwise up?
Tell us the version and the RAM. No database password in the first message.