WordPress, by default, does a form of “Object Caching” but its lifetime is only a single page load. Options are actually a really good example of this. Check out this answer for more info. The summary: A page starts All options are loaded with a simple SELECT option_name, option_value from $wpdb->options statement Subsequent requests for … Read more
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), … Read more
They now are Starting with WordPress 3.7 expired transients are deleted on database upgrades, see #20316 Old answer If someone can’t show me otherwise it seems that transients are not garbage collected after all. What makes it worse is that unlike options they are not guaranteed to be stored in database. So there is no … Read more