mysql全局缓存：
key_buffer_size
innodb_buffer_pool_size
innodb_additional_mem_pool_size
innodb_log_buffer_size
query_cache_size
（局部）线程缓存：
read_buffer_size
sort_buffer_size
read_rnd_buffer_size
tmp_table_size
thread_stack
join_buffer_size
binlog_cache_size