Cache Clearing

MilliCache provides multiple methods to clear cached content, from automatic invalidation to targeted manual clearing.

Automatic Invalidation#Copied!

MilliCache automatically clears cache when content changes:

Post Updates#Copied!

When a post is created, updated, unpublished (trashed, set to draft or private), or deleted:

• The post's URL is cleared
• Related archives are cleared (category, tag, author, date)
• The homepage is cleared
• RSS feeds are cleared

Hooks triggering post-cache clearing:

• clean_post_cache
• before_delete_post
• transition_post_status

Site-Wide Events#Copied!

These events clear the entire site cache:

• Theme switching (switch_theme)
• Menu updates (wp_update_nav_menu)
• Widget updates (widget_update_callback)
• Customizer saves (customize_save_after)
• Template part updates (save_post_wp_template_part)
• Permalink structure changes (update_option_permalink_structure)
• Active plugins changes (update_option_active_plugins)

MilliCache Pro's Block Editor module makes several of these full clears surgical: when a synced pattern, Query Loop source, or Site Editor template changes, exactly the pages using it are cleared instead of the whole site.

Manual Clearing#Copied!

Admin Bar#Copied!

For logged-in users with the publish_pages capability:

1. Click MilliCache in the admin bar
2. Select Clear Site Cache (or Clear Network Cache in multisite)
3. To clear the current page, select Clear Current Page Cache

WP-CLI#Copied!

 1# Clear all cache
 2wp millicache clear
 3
 4# Clear specific posts
 5wp millicache clear --id=1,2,3
 6
 7# Clear by URIs (paths or full URLs)
 8wp millicache clear --uri="/page-1/,/page-2/"
 9
10# Or with absolute URLs
11wp millicache clear --uri="https://example.com/page-1/,https://example.com/page-2/"
12
13# Clear by flags
14wp millicache clear --flag="post:123,home,archive:*"
15
16# Clear specific sites (multisite)
17wp millicache clear --site=1,2,3
18
19# Clear entire network (multisite)
20wp millicache clear --network=1

Expire vs Delete#Copied!

By default, wp millicache clear deletes cache entries immediately. Use --expire to mark them as expired instead:

 1wp millicache clear --expire

Expire behavior:

• Entries remain in cache but marked expired
• Next request serves stale content (grace)
• Content regenerates in background
• Visitors never wait for regeneration

Delete behavior:

• Entries removed immediately
• Next request generates fresh content
• First visitor waits for generation

Flag-Based Clearing#Copied!

MilliCache uses flags (tags) to enable targeted cache clearing. Each cached page is tagged with relevant flags.

Built-in Flags#Copied!

Multisite Flag Prefixes#Copied!

In multisite, flags are prefixed with site/network IDs:

Clearing by Flags#Copied!

 1# Clear homepage
 2wp millicache clear --flag="home"
 3
 4# Clear post and its archives
 5wp millicache clear --flag="post:123,archive:post,home"
 6
 7# Clear all category archives
 8wp millicache clear --flag="archive:category:*"

Programmatic Clearing#Copied!

PHP Functions#Copied!

MilliCache provides helper functions in functions.php:

 1// Clear all cache
 2millicache_reset_cache();
 3millicache_reset_cache( true ); // Expire instead of delete
 4
 5// Clear by post-IDs
 6millicache_clear_cache_by_post_ids( [ 1, 2, 3 ] );
 7millicache_clear_cache_by_post_ids( [ 1, 2, 3 ], true ); // Expire
 8
 9// Clear by URLs
10millicache_clear_cache_by_urls( [
11    'https://example.com/page-1/',
12    'https://example.com/page-2/',
13] );
14
15// Clear by flags
16millicache_clear_cache_by_flags( [ 'post:123', 'home' ] );
17millicache_clear_cache_by_flags( [ 'post:123' ], true ); // Expire
18millicache_clear_cache_by_flags( [ 'post:123' ], false, true ); // Add site prefix
19
20// Clear by mixed targets (Post-IDs, Flags & URLs)
21millicache_clear_cache( 'post:123' ); // Single flag
22millicache_clear_cache( [ 1, 'home', 'https://example.com/page-1/' ] ); // Multiple flags
23
24// Multisite: Clear by site IDs
25millicache_clear_cache_by_site_ids( [ 1, 2 ] );
26millicache_clear_cache_by_site_ids( [ 1, 2 ], 1 ); // Specific network
27
28// Multisite: Clear by network
29millicache_clear_cache_by_network_id( 1 );

Hooks for Custom Clearing#Copied!

Clear cache in response to custom events:

 1// Clear cache when a custom option changes
 2add_action( 'update_option_my_custom_option', function() {
 3    millicache_reset_cache();
 4} );
 5
 6// Clear specific posts when the ACF field updates
 7add_action( 'acf/save_post', function( $post_id ) {
 8    millicache_clear_cache_by_post_ids( [ $post_id ] );
 9} );

Custom Flags#Copied!

Add custom flags to enable targeted clearing:

 1// Add a custom flag based on content
 2add_filter( 'millicache_flags_for_request', function( $flags ) {
 3    // Add a flag for WooCommerce shop
 4    if ( function_exists( 'is_shop' ) && is_shop() ) {
 5        $flags[] = 'woo:shop';
 6    }
 7
 8    return $flags;
 9} );

Then clear by your custom flag:

 1wp millicache clear --flag="woo:shop"

Clearing Actions (Hooks)#Copied!

Hook into clearing events:

 1// After clearing by post-IDs
 2add_action( 'millicache_cache_cleared_by_posts', function( $post_ids, $expire ) {
 3    error_log( 'Cleared cache for posts: ' . implode( ', ', $post_ids ) );
 4}, 10, 2 );
 5
 6// After clearing by flags
 7add_action( 'millicache_cache_cleared_by_flags', function( $flags, $expire ) {
 8    // Notify external CDN
 9    notify_cdn_purge( $flags );
10}, 10, 2 );

Best Practices#Copied!

1. Use Targeted Clearing#Copied!

Clear only what's necessary:

 1// Good: Clear specific content
 2millicache_clear_cache_by_post_ids( [ $post_id ] );
 3
 4// Avoid: Clear everything
 5millicache_reset_cache();

2. Prefer Expire Over Delete#Copied!

For non-critical updates, expire instead of delete:

 1millicache_clear_cache_by_post_ids( [ $post_id ], true ); // expire = true

After a full clear, the first visitor to each page pays the render cost. With Cache Preloading in MilliCache Pro, the cache refills itself from your XML sitemap in the background instead.

3. Batch Related Clears#Copied!

Clear related items together:

 1// Clear post and its relationships
 2$flags = [
 3    "post:{$post_id}",
 4    'home',
 5    'archive:post',
 6];
 7millicache_clear_cache_by_flags( $flags );

4. Use Custom Flags for Cross-Cutting Concerns#Copied!

Add flags for content that should clear together:

 1// Tag all pages showing a promotion
 2add_filter( 'millicache_flags_for_request', function( $flags ) {
 3    if ( is_promotion_active() ) {
 4        $flags[] = 'promo:summer-sale';
 5    }
 6    return $flags;
 7} );
 8
 9// Clear all promotion pages when the sale ends
10millicache_clear_cache_by_flags( [ 'promo:summer-sale' ] );

Next Steps#Copied!

• WP-CLI Commands - Complete CLI reference
• Cache Flags - Understanding flags
• Hooks & Filters - All available hooks