Enabling caching does not mean every request will receive a cached response. Check the cache hit ratio to see how often requests use the cache.
Plan for cache misses even when aiming for a 100% hit ratio. Investigate which requests miss or bypass the cache before changing its settings.
Reasons a Request May Miss the Cache
Check these 8 scenarios:
1. Cache Miss: Simply put, the cache hasn’t saved the requested page yet. This is common for new or rarely visited pages.
2. Cache Bypass: URL parameters, such as UTM tracking codes, can cause the cache to treat requests as different URLs.
3. Cache Expiry: Set the cache’s lifespan too short, and the content might expire too soon, prompting a cache refresh.
4. User Actions: User interactions, like commenting or filling out forms, can lead to a cache clear-out due to dynamic changes.
5. Logged-in Users: Typically, your logged-in user base encounters fresh, uncached content—meaning more load times.
6. Cookie Usage: Certain cookies can trigger cache bypass rules. Check which cookies are set across the site and how the cache handles them.
7. Caching Plugin/Config Issues: Misconfigurations or plugin conflicts can prevent the expected cached response.
8. Server-Side Issues: On occasion, the server might be overwhelmed or facing technical glitches, hampering cached content delivery.
Match the Change to the Cause
Use the findings from those checks to choose the next adjustment.
1. Sidestep the Cache Miss
Pre-cache New Pages: Populate the cache after publishing so the first visitor does not have to create the cached response.
Review the TTL: A longer time to live keeps an entry in the cache longer before it expires.
2. Bypass the Cache Bypass
URL Normalization: Configure the cache to ignore URL parameters that do not change the response.
Selective Caching: Define which responses may be cached and which must bypass the cache.
3. Tackle Cache Expiry
Tune the TTL: Review expiry settings as content and traffic patterns change.
Targeted Purging: Purge affected content after an update instead of clearing the entire cache unnecessarily.
4. Handle Dynamic User Actions
AJAX Updates: Use AJAX for dynamic interactions where they can be handled separately from the cached page.
Partial Caching: Refresh dynamic content separately while retaining the cacheable parts.
5. Serve Logged-in Users Better
Personalized Responses: Keep user-specific content separate from responses shared through the cache.
JavaScript Personalization: Use JavaScript to deliver unique content on the fly without touching the cached materials.
6. Refine Cookie Usage
Selective Cookie Rules: Define the cookies and conditions that require the cache to be bypassed.
Cookie-free Static Assets: Serve static assets without cookies where possible.
7. Clean Up Caching Plugin/Config Issues
Regular Audits: Check cache behavior and configuration during site maintenance.
Resolve Conflicts: Investigate conflicting plugin settings and cache configuration.
8. Strengthen Server-Side Defenses
Review Capacity: Check whether server resources can handle the traffic reaching them.
Load Balancing: Distribute requests across servers where the hosting architecture supports it.
After changing the configuration, check the cache hit ratio again and confirm that pages still return the expected content.
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