Mysql high CPU and RAM usage
join_buffer_size= 8G is dangerously high.  If you have a lot of queries running, all needing the "join buffer", you could quickly run out of RAM, as you appear to have.

8M is a better value for that setting.  Keep in mind that if a query 'wants' a join buffer, it will either use the space you provide or perform the query a different way.

max_connections=8000 is quite high.  What is the status value of Max_used_connections?  If it is more than a few hundred, we should discuss why it is so large.  That could have an impact on memory usage -- many things are "per connection".

Another possibility...  What else is running?  Could it be chewing up RAM?

For a more thorough review, provide SHOW VARIABLES; and SHOW GLOBAL STATUS; (perhaps on some postit site).