Binlog was disabled at last week, this improve the I/O efficiency.
Besides, I've done a minor changes for myisam buffer, changed from 64M to 128M at last week.
query_cache_size=64M
query_cache_limit=2M
join_buffer_size=4M
tmp_table_size=128M
max_heap_table_size=128M
key_buffer_size=90M
OR
query_cache_size (> 32M)
join_buffer_size (> 1.0M, or always use indexes with joins)
tmp_table_size (> 64M)
max_heap_table_size (> 64M)
同时，可以改表的引擎，从myisam到innodb
