In this case, “cachable” refers to server-side caching; allowing a caching mechanism (either the built-in caching system or WP-Cache) to serve cached files instead generating fresh copies upon every visit.
The caching process is this: a visitor a page on your website. This users browser asks your website for the latest version of this page. Your WordPress looks to see if a cached version of that page is available. If it is, it serves that, otherwise creates a cache file and then serves it. When it works well, it’ll not only speed up your site, but save your ISP quite the amount of CPU cycles on the database server. If your site has ever displayed WordPress database error messages or your site just generally feels slow, you can almost certainly benefit from this.
There are, however, a few things to keep in mind when designing a cachable WordPress website:
- Consider the cache expiry time. A long expiry might be needed in extreme cases, whereas a short expiry time will increase the usefulness of certain dynamic fields.
- If you have access to statistics on your webserver, see which of your pages get the most hits, and have those pages designed to be easily cachable.
- Usually, caching your blog homepage and your feed will be enough for most.
In extreme cases:
- Minimize the use of dynamic content on your pages, so no cached information will be obsolete.
- Consider not showing number of comments on your main blog homepage—these will likely turn inaccurate rather quickly.
- Consider using a static date format for your post dates. A static date would be
25/11/1979, whereas a dynamic date would be
27 years, 3 months ago.
- Place comments on separate pages.
- Paginate comments so there is, say, 25 comments per page.