Cloudflare Cuts Cache Bloat, Saves 100 TB RAM by Reducing Hash Entries

How Cloudflare Reduced Hash Entries

Cloudflare announced a second major memory saving effort that targets the core of its caching infrastructure. By redesigning the hash mapping algorithm that determines where cached objects are stored, the company cut the number of hash entries from one hundred thousand to ten thousand. The reduction translates to roughly one hundred terabytes of RAM that are now available for other workloads.

The change is described in detail on the Cloudflare engineering blog. Engineers explain that the previous implementation stored a large number of short‑lived entries that rarely contributed to cache hits. By pruning these entries, the hash table became leaner, more predictable, and far less memory hungry.

Why Hash Tables Matter in a CDN

A content delivery network (CDN) like Cloudflare relies on fast lookup structures to serve billions of requests each day. The hash table theory behind these structures is simple: a key (such as a URL) is transformed into an index that points to the cached object. When the table grows excessively, the system spends more time managing memory than delivering content.

In Cloudflare's case, the oversized hash table caused what engineers call "cache bloat" – a situation where memory is occupied by entries that provide little or no performance benefit. The bloat not only wastes RAM but also increases latency because the lookup process must navigate a larger data set.

Technical Steps Behind the Optimization

The optimization involved three coordinated actions:

1. Analyzing access patterns to identify entries with low hit rates.
2. Re‑engineering the hash function to produce a more uniform distribution, which reduces the need for a large number of buckets.
3. Implementing a dynamic pruning mechanism that removes stale entries before they accumulate.

Each step required close collaboration with standards bodies. The team referenced IETF standards for hash algorithm security and consulted NIST guidelines for memory management best practices.

Impact on Memory Usage

Before the change, Cloudflare's edge servers allocated roughly one hundred terabytes of RAM to store the hash table across its global network. After the reduction, the same servers now use about ten terabytes for the same purpose, freeing ninety percent of the previously consumed memory.

The freed RAM is not left idle. Cloudflare redeploys it to improve other critical functions such as DDoS mitigation, SSL termination, and real‑time analytics. Customers experience faster page loads, lower error rates, and more reliable security features.

Quantifiable Benefits

• Memory savings of approximately one hundred terabytes across the network.
• Reduction of cache miss rate by an estimated five percent.
• Improved latency for high‑traffic sites by up to fifteen milliseconds.
• Lower operational costs due to reduced hardware strain.

Broader Implications for the Industry

Cloudflare's achievement highlights a growing focus on efficiency within the CDN market. As web traffic continues to surge, providers must find ways to do more with less. The approach of tightening data structures, rather than simply adding more hardware, offers a sustainable path forward.

Other CDN operators are likely to examine their own caching layers for similar opportunities. The lesson is clear: regular audits of internal data structures can uncover hidden waste and unlock substantial performance gains.

Best Practices for Operators

Operators seeking to replicate Cloudflare's success should consider the following steps:

1. Collect detailed telemetry on cache hit and miss patterns.
2. Identify hash functions that produce uneven distributions.
3. Implement automated pruning policies that respect content freshness.
4. Validate changes against industry standards to ensure security and compatibility.

By following these practices, organizations can reduce memory pressure, improve response times, and deliver a better experience to end users.

What This Means for End Users

For website owners and visitors, the behind‑the‑scenes work translates into smoother browsing. Faster lookups mean pages render more quickly, especially during traffic spikes. The additional RAM also supports more robust security layers, protecting sites from malicious attacks without compromising speed.

In a world where every millisecond counts, Cloudflare's memory optimisation is a reminder that even mature platforms can find new efficiencies. The result is a faster, safer internet for everyone.