Cache Warming
Filling the Cache Before Visitors Arrive
Cache warming, also called cache preloading, is the practice of filling a cache with copies of pages before real visitors request them. A cache starts empty after a purge, a restart or a deployment. Until a page has been requested once, every visit is a miss, and the origin server builds that page from scratch. Warming sends those requests ahead of time, so the cache is already full when traffic arrives.
Warming is most useful for pages that are popular and slow to build, such as a home page, a category listing or a large archive. Rarely visited pages gain little, so warming usually targets the most requested addresses.
How a Warming Run Works
A warming run requests a list of addresses through the same cache layer that real visitors use. The first request creates the copy, and later visitors are served from it. The list can come from a sitemap, from analytics or from recent access logs. Requests should use the public address, so the cache stores the same version visitors would receive. Many caching plugins include a preloading feature that does this for WordPress sites.
Warming needs care. Sending too many requests at once can overload the origin, which is the very problem warming is meant to prevent. Staggering requests, warming the most important pages first and avoiding personal pages all help. Warming does not replace correct caching rules. It only fills the cache sooner.
Example: Warming After a Catalogue Update
An online shop publishes a new product catalogue at nine in the morning and purges its cache. Within minutes, search engine crawlers and early customers hit uncached pages, and the server slows down. A better routine is to warm the category pages first, then the product pages in batches. Most customers then see cached pages, and the origin handles a steady flow of requests instead of a sudden rush.
Frequently asked questions
Does cache warming make my site faster for everyone?
It mainly helps the first visitor to each page, who would otherwise wait for a slow miss. Warming does not change how long copies stay cached, so warmed pages still expire or get purged like any others. Its value is greatest after large changes, when the cache would otherwise be empty.
Does cache warming improve the cache hit ratio?
Indirectly. A warmed cache starts with more pages stored, so early requests become hits rather than misses. Over time, the ratio depends mostly on how long copies last and how often content changes. The meaning of hits and misses is explained in cache hit vs miss. Warming gives a better start but does not fix a weak caching setup.