Understanding config variables in MySQL
Settings

There is a pecking order of what config files are used.  I hesitate to say exactly what Aurora does, since it is offshoot of MySQL.  First will be /etc/my.chf of /etc/my.ini; last will be .my.cnf in your home directory.  (Note the leading dot.)  Later values will override earlier values.

Be sure to put things in the [mysqld] group in each file.

Be aware that the various settings become visible at different times -- after restart; after re-login; etc.  Also, note that some are "global", some are "session" (and initialized to the global value); etc.  Also note that some can be changed dynamically with a SET command; but, again, there are various variants due to global/session.

Buffer_pool

The main use of memory is for the buffer_pool.


Bigger = faster
Too big --> swapping, and slowdown, or even crash


The default for Aurora is probably optimal for the amount of RAM in the server.  Do not change it.  In the absence of a decent default, set it to about 70% of available RAM for MySQL.