“[W]e just grab the best version that we can find, and manipulate that single source image for whatever size, crop, or filter happens to be requested at the time. That lets us do cool things, like upscaling for Retina displays, as well.” George Stephanis, Jetpack dev
“There’s a script we load with photon that will detect if your user is on a Retina display, and then swap out images for the higher-resolution versions.” George Stephanis, Jetpack dev
Photon filters content but doesn’t change the info in the database.
Photon currently only acts on images in posts and pages, as well as featured images (post thumbnails). Also works for CPTs.
Photon will apply to old posts and new ones alike and can be turned on or off easily.
Photon looks at the img element’s width and height attributes and then serves an image resized to those dimensions or to the width of the containing element (whichever is smaller).
How to use
Enable the Photon module in your Jetpack settings.
SiteGround is an excellent WordPress-optimized shared host. They’re fast, secure, and reliable, yet inexpensive. They’re the host I most frequently recommend to small business and nonprofit clients. From firsthand experience, I’ve found their plans to be superior to similar hosting plans from GoDaddy, Bluehost, DreamHost, Hostmonster, HostGator, iPage, and small local hosting companies.
For e-commerce, don’t cache cart, checkout, my account pages
Queries are controlled by query.php in core
Queries use WP_Query class
Look at query.php and see all the filters available. You may not want to write a custom query; you may be able to modify the main query with pre_get_posts(). It’s more efficient to modify the main query that WordPress is already running than to add a new query. Be very specific about when you’re going to modify the main query; use conditionals.
Querying the database is slow. Use transients to cache data.
Our June 2013 meetup was Improving WordPress Performance. Topher DeRosia, Brian Richards, and Chad Warner talked about various ways to make WordPress sites load faster. Below are the video and notes from the meetup.