Web performance: Cache efficiency exercise

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Ryan Albrecht
•9 min read•intermediate•
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JavaScriptjQueryPHP

Overview

The article discusses the importance of caching for web performance, particularly in the context of Facebook's frequent code releases. It presents a study comparing current cache efficiency with previous research, revealing that a significant percentage of requests still come from an empty cache.

What You'll Learn

1

How to measure cache efficiency using HTTP headers

2

Why frequent code releases can impact cache performance

3

How to analyze cache hit rates across different browsers

Prerequisites & Requirements

  • Understanding of web caching concepts
  • Familiarity with HTTP headers and browser caching mechanisms(optional)

Key Questions Answered

What percentage of requests come from an empty cache at Facebook?
The study found that 25.5% of all logged requests were missing the cache. This was consistent across desktop and mobile platforms, with 24.8% of desktop requests and 26.9% of mobile requests showing similar results.
How does browser cache duration affect performance?
The analysis revealed that there is a 42% chance that any request will have a cache that is at most 47 hours old on desktop. This indicates that caches do not remain populated for long periods, impacting performance.
What factors influence cache hit rates across different browsers?
The study showed that Chrome and Opera users benefited from higher cache hit rates, while Firefox v32 and later versions had reduced logging due to a new cache backend that reuses recent response headers, skewing the results.

Key Statistics & Figures

Percentage of requests missing cache
25.5%
This was observed after collecting data over several weeks.
Percentage of users with an empty cache
44.6%
This statistic reflects the average across all users.
Cache hit rate improvement since 2007
84.1%
This is the adjusted cache hit rate when excluding Firefox v32 and newer.

Technologies & Tools

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Backend
Php
Used to create an endpoint for delivering images and logging requests.

Key Actionable Insights

1
Implementing proper HTTP caching headers can significantly improve cache hit rates.
By using headers like Cache-Control and ETag, developers can ensure that browsers cache resources effectively, reducing load times for repeat visitors.
2
Regularly analyze cache efficiency to adapt to changing web standards and user behaviors.
As web technologies evolve, understanding how caching performs can help maintain optimal website speed and user experience.
3
Consider the impact of frequent code releases on caching strategies.
Frequent updates can lead to a higher percentage of users encountering empty caches, so balancing release frequency with cache management is crucial.

Common Pitfalls

1
Failing to account for browser-specific caching behaviors can lead to inaccurate performance metrics.
Different browsers handle caching differently, and not logging certain requests can skew results, as seen with Firefox v32 and later.

Related Concepts

Web Performance Optimization
HTTP Caching Mechanisms
Browser Compatibility Issues