Caching stores the result of work already done so it does not have to be repeated. It is the single biggest speed improvement available to most sites.
THE LAYERS
Page caching. The finished HTML of a page is saved and served directly to the next visitor, skipping PHP and the database entirely. This is the one that matters most. Object caching. Database query results are stored and reused within the application. Browser caching. Visitors' browsers keep copies of images, CSS and JavaScript so repeat visits download less. CDN caching. Copies of static files are held at locations near your visitors.
ON OUR SERVERS
We run LiteSpeed, so the LiteSpeed Cache plugin can use server-level page caching. That is considerably faster than PHP-based caching plugins, and it is free.
WHAT MUST NEVER BE CACHED
Cart, checkout and account pages. Membership and login pages. Anything showing information specific to one logged-in visitor. Caching these serves one customer's data to another.
Well-known applications are detected automatically by most caching plugins, but custom pages must be excluded by hand.
REMEMBER TO PURGE
After any design change, purge the cache, or you will keep seeing the old version and assume your change did not save.
