In our latest web performance series, we sat down with Harper’s Jeff Darnton to dive into a powerful but often overlooked aspect of web performance strategy: long tail caching. If your team is already leveraging techniques like pre-rendering, redirects, and early hints, long tail cache might be your next lever for unlocking performance gains and reducing cloud costs at scale.

Let’s break down what it is, why it matters, and how Harper is helping companies make it easy to implement.

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What Is Long Tail Caching?

At its core, long tail caching is a strategy to store and serve infrequently accessed content closer to the end user. These “long tail” assets—things like obscure product pages, rarely used service manuals, or niche images—may not be requested often, but when they are, speed matters.

Traditional caching systems, like CDNs, are fantastic at serving frequently requested assets. But their request-driven content is only cached after someone asks for it. Less popular content doesn’t get cached—or gets evicted quickly due to shared cache limits—leading to slow experiences or costly origin fetches.

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Why the Long Tail Matters

Even if a file is only requested once a month, that moment can still be critical. Jeff shared a story where engineers needed to access 3GB PDF manuals for specific aircraft models. If that file wasn’t already downloaded, the plane could be delayed while waiting for it to load over a slow network. In these cases, minutes matter and have a tangible impact on profit and customer satisfaction.

This story illustrates two key business drivers for long tail caching:

• Performance: Serving content closer to users accelerates page load, improves conversions, and ensures critical workflows (like airplane maintenance) don’t stall.
• Cost: Every origin request incurs egress costs—fees cloud providers charge when data leaves their environment. Reducing origin traffic means cutting real dollars off your monthly cloud bill.

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The Limits of CDNs (And the Real Cost of Cache Misses)

While CDNs are essential for modern web applications, they weren’t built to cache everything. Cache eviction policies like LRU (least recently used) and FIFO (first in, first out) mean that even long TTLs (time-to-live) don't guarantee persistence—especially if the content isn’t accessed frequently.

Even worse, most CDNs and their geographically distributed caches don’t share state. So if your asset is requested in New York, that doesn’t help a user in Sydney—those requests will still need to go back to origin.

Multiply that across regions, languages, currencies, and catalog variations, and suddenly, your long tail is massive—and expensive.

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Quantifying the Opportunity: Origin Offload Metrics

One of the key ways to measure cache effectiveness is origin offload: the percentage of requests served from cache vs. origin. Jeff offered some benchmarks:

• API or dynamic content: Aim for 50%+ offload
• HTML/base pages: Target 60–70%
• Static assets (images, video, CSS, JS): Shoot for 90%+
  
  

That last 10% of cache misses—often the long tail—can be the most difficult to reach. However, it also holds a major opportunity, both in performance and cost savings.

For retailers with tens of millions of SKUs and variants, every percentage point of offload can translate into millions in reduced egress fees.

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Passive vs. Active Cache: Why Strategy Matters

Most CDNs operate as passive caches: they wait for requests. But to truly optimize long tail content, you need an active strategy.

Harper allows teams to pre-populate caches based on schedules, events (like publishing), or user behavior. This proactive approach ensures that even infrequently accessed content is already waiting at the edge—reducing latency and eliminating origin hits.

It’s not just about web pages. Harper customers actively cache:

• GraphQL and REST API responses
• Pricing and inventory calls
• Media files (Images and Video)
• CSS and JavaScript bundles
• PDFs and other heavy documents

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Standing Up a Long Tail Cache with Harper

Implementing long tail caching on Harper is fast. The more important step is integrating it into your workflow:

• Do you want Harper to pull content based on a list or crawl?
• Do you want to push content during your publishing cycle?
• Do you want to observe user traffic to determine what to cache?
  
  

Once configured, Harper offers complete control: cache size, geographic placement, TTL, refresh rules, and more. It also works alongside your existing CDN—serving as a second-tier cache that reduces cloud dependency and unlocks higher offload and better performance.

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Start with the Why

The key to successful caching isn’t just technical—it’s strategic. Start by identifying why you want to cache:

• Faster performance for end users?
• Lower cloud costs?
• Higher conversion rates?
• Better availability in multi-region apps?
  
  

From there, evaluate what you're caching today, identify the gaps, and align on the targets that matter to your business.

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Ready to Cache Smarter?

If you’re already investing in web performance, don’t let long tail content become a blind spot. With Harper, it’s possible to cache more content, more intelligently—without rewriting your entire architecture.

Want help getting started? We’ll work with you to assess your caching strategy, pinpoint opportunities, and stand up a Harper cache that works with your existing infrastructure. Click here to get in touch with an engineer. 

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