When multisite is 'on' too many database queries are called, and bursts network bandwidth between web server and database server.
The query is below.
"SELECT option_name, option_value FROM wp_options WHERE autoload = 'yes'"
This is caused by a limitation of object cache and multisite.
When multisite is on, wordpress cannot use wp_cache_get for that query in wp_load_alloptions function.
Moreover, wp_load_alloptions is called when each get_option function is executed.
If wp_options table has huge data (ex. serialized 'rewrite_rule'), it costs so many time.
Perhaps, it's a solution of multisite confusion by wp_cache_get, but it causes another problem.
I think, even no object cacheing is better than so many database query.