---
title: "What is a cache purge? Purge vs. invalidation vs. expiry — warmup.rocks Glossary"
description: "A purge removes cached content from a CDN on demand. Purge-by-URL vs. purge-everything vs. tag-based invalidation, what each costs you in cold caches, and why purging without re-warming hurts."
canonical: https://warmup.rocks/glossary/cache-purge
---

# Cache purge

A **cache purge** removes content from a CDN's caches on demand, before its [TTL](https://warmup.rocks/glossary/ttl) would expire it — the tool for "the content changed, stop serving the old version." The flip side: every purge manufactures cold caches, and the first visitor afterwards pays for it.

## The purge spectrum

| Method | Scope | Cold-cache damage |
| --- | --- | --- |
| Purge by URL | Exact [cache keys](https://warmup.rocks/glossary/cache-key) | Minimal — only changed objects go cold |
| Purge by tag / surrogate key | All objects labeled with a tag (e.g. `product-42`) | Proportional — precise if your tagging is |
| Purge by prefix / wildcard | Path subtrees | Broad |
| Purge everything | The entire zone | Total — every URL at every [PoP](https://warmup.rocks/glossary/point-of-presence) is a miss again |

Tag-based purging (Fastly's surrogate keys, Cloudflare cache tags) is the precision tool: tag each page with the entities it renders, then purge the tag when an entity changes. Purge-everything is the blunt default in most deploy pipelines — convenient, and by far the most destructive to your [hit ratio](https://warmup.rocks/glossary/cache-hit-ratio).

## Purge ≠ invalidation, strictly speaking

Some systems distinguish hard purge (delete the object) from soft purge/invalidation (mark it stale but keep the bytes). A soft-purged object can still be served under [stale-while-revalidate](https://warmup.rocks/glossary/stale-while-revalidate) or `stale-if-error` semantics while the cache refreshes — visitors keep cache speed even during the transition. Prefer soft purges where your CDN offers them.

## Purge and re-warm belong together

A purge without a warming pass hands your miss penalty to real visitors — at the median a miss is 3.5× slower, [per our production measurement](https://warmup.rocks/blog/cdn-cache-miss-data). The clean deploy sequence is: deploy → purge (as narrowly as possible) → re-warm the affected URLs from every region, automatically. That last step is what [deploy hooks](https://warmup.rocks/docs/deploy-hooks) exist for.