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.

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, with proper configuration:

 1define( 'MC_CACHE_NOCACHE_COOKIES', [
 2    'wp-*pass*',
 3    'comment_author_*',
 4    'woocommerce_cart_hash',
 5    'woocommerce_items_in_cart',
 6] );
 7
 8define( 'MC_CACHE_NOCACHE_PATHS', [
 9    '/my-account/*',
10    '/checkout/*',
11    '/cart/*',
12] );

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)

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_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

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!