FAQ

Frequently asked questions about MilliCache.

General Questions#Copied!

What is MilliCache?#Copied!

MilliCache is a full-page caching plugin for WordPress that stores complete HTML pages in Redis (or compatible stores like ValKey, KeyDB, or Dragonfly). When a visitor requests a cached page, MilliCache serves it directly from memory without loading WordPress, resulting in sub-10ms response times.

How is MilliCache different from other caching plugins?#Copied!

Feature MilliCache Other Plugins
Storage Redis/ValKey/KeyDB Files/Database
Speed Sub-10ms 50-200ms
Rules Engine MilliRules (powerful) Basic conditions
Flag-based Invalidation Yes Limited
Multisite Full support Varies
License GPL-2.0+ Varies

Does MilliCache require Redis?#Copied!

Yes, MilliCache requires a Redis-compatible server. Supported options:

  • Redis (original)
  • ValKey (open-source fork)
  • KeyDB (multithreaded)
  • Dragonfly (high-performance)

Is MilliCache free?#Copied!

Yes, MilliCache is free and open-source under GPL-2.0+ license.

Is there a Pro version?#Copied!

Yes. MilliCache Pro adds premium modules on top of the free plugin: a cache entries browser, a visual rules builder, block editor cache intelligence, preloading, detailed metrics, edge caching, an asset CDN, and a persistent object cache. It bundles MilliCache, so it replaces the free plugin rather than running alongside it.

Installation & Setup#Copied!

What are the requirements?#Copied!

  • PHP 7.4 or higher
  • WordPress 5.6 or higher
  • Redis, ValKey, KeyDB, or Dragonfly server

How do I know if caching is working?#Copied!

  1. Enable debug mode:

     1define( 'MC_CACHE_DEBUG', true );

  2. Visit a page (logged out)

  3. Check response headers:

    • First visit: X-MilliCache-Status: miss
    • Second visit: X-MilliCache-Status: hit

Do I need to configure anything after installation?#Copied!

Basic setup requires:

  1. Add to wp-config.php:

     1define( 'WP_CACHE', true );

  2. Install the drop-in:

     1wp millicache drop

If Redis runs on default settings (localhost:6379), no additional configuration is needed.

Caching Behavior#Copied!

What gets cached?#Copied!

Cached:

  • GET and HEAD requests
  • 200 OK responses
  • Anonymous visitors (logged-out)
  • Pages, posts, archives, taxonomies
  • RSS feeds (by default)

Not Cached:

  • POST, PUT, DELETE requests
  • Logged-in users
  • Non-200 responses
  • AJAX, REST API, XML-RPC, Cron
  • WP-CLI commands

Why aren't logged-in users cached?#Copied!

Logged-in users see personalized content (admin bar, user-specific data). Caching would show incorrect content. This is a security and UX best practice.

Can I cache logged-in users?#Copied!

It's not recommended. If you need it:

  1. Remove the logged-in rule via filter
  2. Add user-specific flags
  3. Ensure no sensitive data leaks
Warning: Caching logged-in users can expose private data. Only do this if you fully understand the implications.

What is the grace period?#Copied!

The grace period allows stale cache to be served while fresh content generates in the background. This prevents visitors from waiting for page generation after cache expires.

Example with TTL=1 day, Grace=30 days:

  • Day 1: Fresh cache served
  • Day 2: Cache expired, but grace serves stale while regenerating
  • Day 31: Grace expired, visitor waits for fresh content

How does cache invalidation work?#Copied!

MilliCache uses flags (tags) for targeted invalidation:

  1. Each page is tagged with flags (e.g., post:123, home, archive:post)
  2. When content changes, related flags are identified
  3. Only pages with matching flags are cleared

This means updating one post doesn't clear the entire cache—only affected pages.

Compatibility#Copied!

Does MilliCache work with WooCommerce?#Copied!

Yes, and the critical pages are safe out of the box: WooCommerce sets the DONOTCACHEPAGE constant on the cart, checkout, and my-account pages, and a built-in MilliCache rule respects it. You do not need path exclusions for a standard setup.

What you should configure is cookie handling. WooCommerce sets several cookies for ordinary browsing visitors, and any cookie MilliCache does not ignore becomes part of the cache key, which fragments the cache into per-visitor variants:

  • sbjs_*: Order Attribution tracking (Sourcebuster), set for every visitor
  • store_notice*: set when a visitor dismisses a store notice
  • woocommerce_cart_hash, woocommerce_items_in_cart, wp_woocommerce_session_*: set once something is in the cart
  • woocommerce_recently_viewed: set on product views, but only while the classic Recently Viewed Products widget is active

The tracking, store-notice and recently-viewed cookies never change the HTML WooCommerce builds, so ignore them. The store notice is rendered hidden and revealed by JavaScript, and only the classic widget covered below reads the recently-viewed cookie on the server. The cart and session cookies are usually safe too: most themes refresh the mini cart client-side, via cart fragments in classic themes or the Store API in the Mini-Cart block. But a theme or extension can render cart contents on the server, so check first: open a product page in two private windows with different carts and compare the page sources. If they match, ignore the cart cookies as well:

 1define( 'MC_CACHE_IGNORE_COOKIES', [
 2    '_*',                        // Keep the default (analytics cookies)
 3    'sbjs_*',
 4    'store_notice*',
 5    'woocommerce_*',
 6    'wp_woocommerce_session_*',
 7] );

If you use the classic Recently Viewed Products widget, list the cart cookies by name (woocommerce_cart_hash, woocommerce_items_in_cart) instead of woocommerce_*: the widget builds its list from woocommerce_recently_viewed on the server, so ignoring that cookie would serve one visitor's list to everyone.

Do not put woocommerce_* or sbjs_* into MC_CACHE_NOCACHE_COOKIES. sbjs_* is set for every visitor, and with the classic widget active woocommerce_recently_viewed is set on the first product view, so a blanket bypass silently turns most of your browsing traffic into cache misses.

Two exceptions:

  • If the page sources differ because your theme renders cart contents server-side, bypass for visitors with a cart instead of ignoring: add woocommerce_items_in_cart to MC_CACHE_NOCACHE_COOKIES.

  • If you use custom dynamic pages WooCommerce does not know about (a custom order tracking page, for example), exclude them by path:

     1define( 'MC_CACHE_NOCACHE_PATHS', [ '/order-tracking/*' ] );

To verify the result, watch the hit ratio on the Status tab after deploying the configuration. MilliCache Pro makes this much easier to inspect: the Cache Entries Browser lists every cached page with its variants, so you can see exactly what gets cached and spot cookie-driven fragmentation, and Detailed Metrics charts the hit ratio over time.

Does MilliCache work with membership plugins?#Copied!

Yes. Common configurations:

 1// MemberPress
 2define( 'MC_CACHE_NOCACHE_COOKIES', [
 3    'wp-*pass*',
 4    'memberpress_*',
 5    'mepr_*',
 6] );
 7
 8// Restrict Content Pro
 9define( 'MC_CACHE_NOCACHE_COOKIES', [
10    'wp-*pass*',
11    'rcp_*',
12] );

Can I use MilliCache with a CDN?#Copied!

Yes! MilliCache caches at the origin server. CDN caches on edge servers. They work together:

  1. CDN checks its cache
  2. CDN miss → Request reaches origin
  3. MilliCache serves from Redis (fast!)
  4. CDN caches the response

For cache clearing, you may need to:

  • Clear MilliCache (origin)
  • Clear CDN (edge)

MilliCache Pro's Edge Cache module automates exactly this: pages are tagged at the CDN with the same flags they carry locally, and every local purge triggers the matching edge purge.

Does MilliCache work with Cloudflare/other proxies?#Copied!

Yes. MilliCache operates at the origin level, before any proxy/CDN.

Does MilliCache conflict with other caching plugins?#Copied!

Yes, you should only use one full-page caching plugin. Deactivate others before using MilliCache:

  • WP Super Cache
  • W3 Total Cache
  • WP Fastest Cache
  • LiteSpeed Cache
  • etc.

Object caching plugins (Redis Object Cache) are fine — they cache different things.

Multisite#Copied!

Does MilliCache support multisite?#Copied!

Yes, fully. Features include:

  • Per-site cache isolation
  • Multi-network support
  • Site and network-level clearing
  • Per-site configuration options

How do I clear cache for one site only?#Copied!

 1# By site URL
 2wp millicache clear --url=site1.example.com
 3
 4# By site ID
 5wp millicache clear --site=2

How do I clear cache for all sites?#Copied!

 1# All sites in network
 2wp millicache clear --network=1
 3
 4# All cache (all networks)
 5wp millicache clear

Performance#Copied!

How fast is MilliCache?#Copied!

Scenario Typical Response Time
Cache hit 5-15ms
Cache miss (WordPress) 200-2000ms

That's 10-200x faster than uncached WordPress.

How much memory does MilliCache use?#Copied!

Memory usage depends on:

  • Number of cached pages
  • Average page size
  • Compression enabled

Typical usage with 1000 pages:

  • Without compression: ~50-100MB
  • With compression: ~15-30MB

Should I enable compression?#Copied!

Yes, for most sites:

 1define( 'MC_CACHE_GZIP', true );

Benefits:

  • 60-80% smaller cache entries
  • Lower memory usage
  • Faster cache retrieval

Requires ext-zlib PHP extension.

WP-CLI#Copied!

What commands are available?#Copied!

Command Description
wp millicache clear Clear cache
wp millicache stats View statistics
wp millicache status Check status
wp millicache test Test connection
wp millicache drop Fix drop-in
wp millicache cli Open Redis CLI
wp millicache config Manage settings

How do I clear cache via cron?#Copied!

 1# Add to crontab
 20 3 * * * cd /path/to/wordpress && wp millicache clear --expire

The --expire flag serves stale content while regenerating (gentler).

Security#Copied!

Does MilliCache cache sensitive data?#Copied!

MilliCache does not cache:

  • Logged-in users
  • POST requests
  • Pages with excluded cookies

This prevents accidental caching of sensitive data.

Is the Redis connection secure?#Copied!

For security:

  1. Use authentication: MC_STORAGE_USERNAME and MC_STORAGE_PASSWORD
  2. Bind Redis to localhost if on same server
  3. Use private networks for remote Redis
  4. Consider Redis TLS for sensitive environments

Does MilliCache modify WordPress core?#Copied!

No. MilliCache uses WordPress's official drop-in caching API (advanced-cache.php). It doesn't modify core files.

Troubleshooting#Copied!

Why isn't my page being cached?#Copied!

Check debug headers (MC_CACHE_DEBUG = true):

Status Meaning
No headers Drop-in not installed
bypass Rule prevented caching
miss First request, will cache
hit Cached and serving

Common bypass reasons:

  • Logged in
  • Excluded cookie
  • Excluded path
  • POST request
  • Non-200 response
  • Response larger than 5MB

Why is cache not clearing?#Copied!

  1. Clear manually: wp millicache clear
  2. Check Redis connection: wp millicache test
  3. Verify clearing hooks: Check millicache_cache_cleared action
  4. Clear external caches (CDN, proxy)

Where can I get help?#Copied!

Next Steps#Copied!

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