I get this message from MysqlTunner.pl:
join_buffer_size >= 4 M This is not advised
On the other hand, I read in Debian's my.cnf guide about jont_buffer_size that:
This buffer is used for the optimization of full JOINs (JOINs without indexes). Such JOINs are very bad for performance in most cases anyway, but setting this variable to a large value reduces the performance impact. See the "Select_full_join" status variable for a count of full JOINs. Allocated per thread if full join is found
So I'm wondering which one should I believe? Currently I've set join_buffer_size = 64M as part of efforts to cope with scalability problem of a high-traffic site whose queries are not particularly optimized. I appreciate your hints on this.