Why Magento Full Page Cache (FPC) Fails Real Performance Audits (Even with Hyvä)

A Hyvä demo store can feel lightning fast - until you disable Full Page Cache (FPC). FPC masks backend slowness by serving pre-rendered HTML, hiding the real cost of generating uncached pages. This article explains why Magento 2 FPC isn’t the full picture, how to reveal hidden bottlenecks, and how tools like mage-scan.com expose the truth.

1. What Full Page Cache Really Does

Magento’s FPC stores the full HTML output of a page and serves it instantly on repeat visits. This drastically reduces Time To First Byte (TTFB) for cached pages. But it doesn’t improve the performance of uncached pages - like first visits, logged-in customer views, or dynamic pages with personalized content.

In performance audits, relying solely on cached metrics can hide problems in database queries, block rendering, and third-party module overhead.

2. Why Hyvä Demos Feel Faster Than Reality

Hyvä’s frontend is lean - minimal JS, TailwindCSS, Alpine.js - so cached pages load very fast. But when FPC is bypassed, backend processing time becomes visible. If a Hyvä store still has slow indexers, heavy layout XML, or inefficient module logic, those issues remain hidden until a cache miss occurs.

This gap is why real performance testing must include both cached and uncached scenarios.

3. Common Reasons FPC Gets Bypassed

• Logged-in customer sessions
• Cart or wishlist changes
• Dynamic blocks with private content
• Custom modules that disable FPC for certain routes
• Incorrect cache tags or invalidation rules

If these scenarios take several seconds to render, it’s a backend problem - not an FPC problem.

4. How to Measure True Backend Performance

To uncover backend slowness, test with FPC disabled:

bin/magento cache:disable full_page

Then use profiling tools to track execution time for:

• Database query count and execution time
• PHP block rendering time
• Layout XML processing cost
• Third-party module observers and plugins

Tools like mage-scan.com provide a quick audit of installed modules, flagging performance-heavy code and JS/CSS payloads that Hyvä’s minimalism otherwise hides.

5. Fixing Backend Bottlenecks

Once you’ve identified slow components, focus on:

• Removing unused or outdated extensions
• Optimizing database queries and adding missing indexes
• Reducing layout XML complexity
• Replacing heavy modules with Hyvä-compatible qoliber modules

These steps improve both cached and uncached page performance, ensuring FPC is an optimization - not a crutch.

6. Testing After Optimization

Re-enable FPC and test again:

bin/magento cache:enable full_page

Compare metrics for both cached and uncached pages. A well-optimized Magento 2 + Hyvä build should serve uncached pages quickly and have negligible difference between the two states.

Conclusion

Full Page Cache is powerful, but it’s not a silver bullet. In Magento 2, and even with Hyvä, backend bottlenecks can hide behind FPC’s speed. By auditing with FPC disabled and using tools like mage-scan.com, developers can expose the real performance profile, fix underlying issues, and deliver consistently fast experiences - cached or not.