Varnish HTTP Purge

This plugin does not install nor configure a cache proxy. It acts as an interface with such services.

One common method of caching content for websites is via the use of reverse proxy caching. Common examples of this are Varnish and NGINX. These systems allow a website to update content and have the visitor’s experience cached without the need for complex plugins storing the files locally and using up a user’s disk space.

A reverse proxy cache is installed in front of a server and reviews requests. If the page being requested is already cached, it delivers the cached content. Otherwise it generates the page and the cache on demand.

The Proxy Cache Purge plugin sends a request to delete (aka flush) the cached data of a page or post every time it’s modified.

How It Works

When content on a site is updated by WordPress, the plugin reaches out to the proxy cache service with the URL of the page, requesting the cache be deleted.

Not all pages are deleted from the cache on every change. For example, when a post, page, or custom post type is edited, or a new comment is added, only the following pages will purge:

• The front page
• The post/page edited
• Any categories, tags, and/or custom taxonomies associated with the page
• Related feeds
• Associated JSON API pages

In addition, your entire cache will be deleted on the following actions:

• Changing themes
• Pressing the Empty Cache button on the toolbar

Plugins can hook into the purge actions as well, to filter their own events to trigger a purge.

On a multisite network using subfolders, only network admins can purge the main site.

Development Mode

If you’re working on a site and need to turn off caching in one of two ways:

1. Add define( 'VHP_DEVMODE', true ); to your wp-config.php file
2. Go to Proxy Cache -> Settings and enable Debug Mode for 24 hours at a time

That will break cache on page loads. It is not recommended for production!

Cache Tags (BETA)

As of version 5.4.0, Proxy Cache Purge includes an optional Cache Tags / Surrogate Keys purge mode. This feature is marked as BETA and is disabled by default.

When enabled, the plugin:

• Adds cache-tag headers to WordPress responses (for example, tagging pages by post ID, post type, taxonomy terms, author, and archives).
• Uses tag-based purges instead of individual URL purges when content is updated, which can reduce purge traffic and improve consistency on complex sites.

Requirements:

• A proxy cache that supports Cache Tags / Surrogate Keys and advertises this via standard Surrogate-Capability headers (for example, Surrogate-Capability: vhp="Surrogate/1.0 tags/1").

How to enable:

• Go to Proxy Cache → Settings → Purge Method and check “Use Cache Tags (Surrogate Keys)”. The checkbox is only enabled when your cache tells WordPress it supports tags (or when you explicitly enable it via a define).

• Alternatively, you can force-enable or force-disable detection via wp-config.php:

  define( ‘VHP_VARNISH_TAGS’, true ); // Force treat cache as tag-capable
  define( ‘VHP_VARNISH_TAGS’, false ); // Force treat cache as not tag-capable

Because this feature depends on your cache configuration, it is recommended that you test it carefully in staging before enabling it on production.

Background Purging with WP-Cron

On busy sites, sending many PURGE requests directly from admin requests can slow things down. When you define DISABLE_WP_CRON as true in wp-config.php (because you are running a real system cron that calls wp-cron.php), Proxy Cache Purge automatically switches to an asynchronous mode:

• Purge requests (both URL-based and tag-based, when Cache Tags are enabled) are collected into a small per-site queue.
• The queue is processed by WP-Cron in the background, keeping your admin and content-editing actions responsive even when many URLs or tags must be invalidated.

Object-cache purges (the “Purge Database Cache” option) remain synchronous and are not affected by this behaviour. The Proxy Cache settings page and Site Health integration expose basic queue status so you can verify that background purging is healthy; if the queue appears large or very old, check that your system cron is correctly invoking WordPress cron.

Important: Cron Frequency and Cache Freshness

When using background purging, the frequency of your system cron determines how quickly cache invalidations are processed. The longer the interval between cron runs, the longer visitors may see stale content after updates.

For minimal stale content, run your system cron every minute:

* * * * * /usr/bin/php /var/www/html/wp-cron.php

If you can tolerate slightly longer delays, every 2-5 minutes is also acceptable. However, running cron less frequently (e.g., every 15 minutes) means cache purges may be delayed by that amount after content changes.

Note: Scheduled posts are handled specially. When a scheduled post is published via WP-Cron, the cache is purged synchronously within the same cron run, ensuring immediate cache invalidation without waiting for the next cron execution.

For detailed instructions on setting up a proper Linux-based WordPress cron, see: WordPress Cron Optimization.

WP-CLI

Purge

Purge commands let you empty the cache.

• wp varnish purge – Flush the entire site cache (equivalent to clicking “Empty Cache” in admin)
• wp varnish purge --all – Explicitly flush the entire site cache
• wp varnish purge <url> – Flush cache for a specific URL and all content below it (wildcard)
• wp varnish purge <url> --url-only – Flush cache for only the exact URL specified (no wildcard)
• wp varnish purge --tag=<tag> – Flush cache by tag (requires Cache Tags mode to be enabled)

Examples:

• wp varnish purge – Purge entire site
• wp varnish purge --all – Same as above, more explicit
• wp varnish purge https://example.com/hello-world/ – Purge this URL and everything below it
• wp varnish purge https://example.com/hello-world/ --url-only – Purge only this exact URL
• wp varnish purge https://example.com/wp-content/themes/ --wildcard – Purge all theme files
• wp varnish purge --tag=p-123 – Purge all pages tagged with post ID 123
• wp varnish purge --tag=pt-post – Purge all cached pages of post type “post”

Debug

Debugging can help you figure out why your cache isn’t working as well as it could. The default is for your home page, but you can pass any URL on your domain.

• wp varnish debug [<url>]

Available parameters:

• [--include-headers] — Include headers in debug check output
• [--include-grep] — Grep active theme and plugin directories for common issues

DevMode

Development mode allows you to disable the cache, temporarily.

• wp varnish devmode [<activate|deactivate|toggle>] – Change development mode state

Async purge queue (cron-mode)

When you define DISABLE_WP_CRON as true and run a real system cron for WordPress, Proxy Cache Purge can move heavy purge work into a small background queue that is processed by WP‑Cron.

You can inspect and manage that queue via WP‑CLI:

• wp varnish queue status – show whether cron-mode is active, if a full purge is queued, counts of queued URLs/tags, and the last queue run time.
• wp varnish queue process – process any items currently in the queue (useful to run after deploys or cache‑sensitive operations).
• wp varnish queue clear – clear the queue without sending any PURGE requests.

These commands do not replace your normal WordPress cron (you still need a cron entry that calls wp cron event run --due-now or hits wp-cron.php), but they give you a simple operational handle when using cron‑mode.