Server Cache (Page Cache)

Server cache (page cache) stores the final HTML output for a URL so repeat requests can be served without running PHP or hitting the database. For most WordPress sites, this is the biggest TTFB win because it removes the entire WordPress bootstrap for cache hits.

What a Cache Hit Looks Like

page-cache-hit-vs-miss.txt

Request -> Web server
  -> Cache lookup
     HIT: return cached HTML (no PHP/DB)
     MISS: run PHP -> WordPress -> DB -> build HTML -> store -> return

What Should (and Shouldn't) Be Cached

Cache is safest and most effective for:

• Public pages for anonymous visitors (home, posts, categories, product pages)

Cache should be bypassed for:

• POST requests
• wp-admin, wp-login.php
• Logged-in sessions
• WooCommerce cart/checkout/account
• Requests that change state (example: ?add-to-cart=)

caution

If you cache personalized pages publicly, you can serve the wrong content to the wrong user. Always treat authentication cookies and cart/account routes as cache-bypass until proven safe.

Implementation Patterns

LiteSpeed (LSCache)

LiteSpeed has first-class WordPress support through the LiteSpeed Cache (LSCache) plugin.

Minimum baseline:

• Enable page cache for guests
• Exclude cart/checkout/account
• Keep cache purge predictable

Verify with headers:

curl-litespeed-cache-header.sh

curl -I https://example.com/ | grep -i x-litespeed

Typical signals:

litespeed-cache-hit.txt

x-litespeed-cache: hit

Nginx FastCGI Cache

FastCGI cache stores the HTML output produced by PHP-FPM and serves it on subsequent GET/HEAD requests.

Example (simplified) configuration:

/etc/nginx/conf.d/fastcgi-cache.conf

fastcgi_cache_path /var/run/nginx-cache levels=1:2
                 keys_zone=WORDPRESS:100m
                 max_size=1g
                 inactive=7d
                 use_temp_path=off;

fastcgi_cache_key "$scheme$request_method$host$request_uri";

/etc/nginx/sites-available/example.com

server {
  set $skip_cache 0;

  if ($request_method = POST) { set $skip_cache 1; }
  if ($query_string != "") { set $skip_cache 1; }
  if ($http_cookie ~* "wordpress_logged_in|comment_author|wp_woocommerce_session") { set $skip_cache 1; }
  if ($request_uri ~* "/cart|/checkout|/my-account") { set $skip_cache 1; }
  if ($request_uri ~* "add-to-cart=") { set $skip_cache 1; }

  location ~ \.php$ {
    fastcgi_cache WORDPRESS;
    fastcgi_cache_valid 200 7d;
    fastcgi_cache_bypass $skip_cache;
    fastcgi_no_cache $skip_cache;

    add_header X-FastCGI-Cache $upstream_cache_status;

    fastcgi_pass unix:/var/run/php/php8.2-fpm.sock;
    include fastcgi_params;
  }
}

Verify:

curl-nginx-fastcgi-cache-header.sh

curl -I https://example.com/ | grep -i x-fastcgi-cache

Varnish

Varnish is an HTTP reverse proxy cache. It is extremely fast, but it adds an extra operational layer (VCL rules, purge workflows, health checks).

Use Varnish when:

• You already operate reverse proxies and want an explicit caching tier
• You need advanced caching logic beyond what your origin server provides

Verify (example):

curl-varnish-signals.sh

curl -I https://example.com/ | grep -iE 'x-varnish|age|via|cache'

Purge Strategy

Cache only works when you purge predictably.

• Prefer selective purges (page + related archives) instead of purging everything.
• Purge after theme/plugin updates.
• If you publish frequently, consider a warmup/crawler to avoid cold-cache spikes.

Example (LSCache via WP-CLI):

litespeed-purge.sh

wp litespeed-purge all

note

WP-CLI purge commands depend on your cache plugin exposing a WP-CLI command.

Common Problems

Symptom	Likely Cause	Fix
Cached pages still slow	Cache misses	Check bypass rules, query strings, and cookies; verify headers
Logged-in users see cached HTML	Missing cookie bypass	Bypass when wordpress_logged_in_ is present
Cart/checkout issues	Transactional routes cached	Exclude /cart, /checkout, /my-account and test flows
Low hit rate	Too many variants	Reduce unnecessary varies (device, query strings, language)

What's Next

• CDN Cache
• ESI for WooCommerce
• Object Cache (Redis)
• Cache Strategy Checklist