Are all options variables fetched from the database and loaded to cache on each request?
Yes, sort of. When the
get_option call is made, WordPress runs a function called
wp_load_alloptions, which either grabs a cached copy of all autoloaded options or loads all those options into the cache. Then
wp_load_alloptions returns an array of all the autoloaded options. If your option is autoloaded (specified when you use the
add_option function), it will be part of this array and get returned.
If your option is not auto loaded, WordPress then looks in the cache specifically for that option and returns the value if it's there. If that misses, the final fallback is to go to the database, fetch the value, set it the cache and then return it.
Finally, if no option is found at all (eg. the option name was invalid), WordPress stores that option's name in a cached array called
notoptions. If subsequent calls to the non-option are made, WP checks the notoptions array first so it doesn't waste time checking for something that isn't there.
If you're worried about calling
get_option multiple times per page load, don't be. WordPress will cache the option value after the first
get_option call regardless of whether or not its autoloaded.
Check out the source for
get_option to see what's going on.
only the options that are specifically loaded with autoload set to true
So if it is an option that is needed on every page, when you add it to the db, set autoload=true.
After that, just use get_option normally - wp will handle the cacheing etc.
There is no need to set autoload to yes/true. It is set to yes by default: http://codex.wordpress.org/Function_Reference/add_option - last function parameter ($autoload):
Should this option be automatically loaded by the function wp_load_alloptions() (puts options into object cache on each page load)? Valid values: yes or no. Default: yes
Though, if you set it to no, then the option won't be put in cache.