The Original, Blazing-Fast, In Memory Cache. Still Relevant, Still Dangerous.
Before there was Redis, there was Memcached. Born at LiveJournal and made famous by Facebook, it is a high performance, distributed memory object caching system designed for one purpose: to speed up dynamic web applications by alleviating database load. Its simplicity is its greatest strength. It is a pure, no-frills, in memory key-value store. It is incredibly fast and incredibly simple.
But this simplicity is deceptive. An engineer who treats Memcached as a permanent data store, or who doesn't understand how client side hashing and consistent hashing work to distribute data across a cluster, will build a system that is brittle and prone to "thundering herd" problems. Understanding when to use Memcached (for simple, volatile caching) versus a more feature rich tool like Redis (which offers persistence and complex data structures) is a key architectural decision.
This playbook explains how Axiom Cortex vets for a deep, practical understanding of distributed caching principles, finding engineers who can wield tools like Memcached effectively to build blazingly fast applications.
Traditional Vetting and Vendor Limitations
A vendor who can vet for deep caching expertise is rare. Most will see "Memcached" on a résumé and assume basic competence. This fails to test for the critical skills in distributed systems thinking that are essential for building a reliable caching layer.
The result of this superficial vetting is an application with a caching layer that causes more problems than it solves:
- The "Cache Stampede": A popular cached item expires, and thousands of concurrent requests simultaneously try to regenerate it by hitting the database, causing a massive load spike and bringing the application down.
- The Inconsistent Cluster: When a new Memcached server is added to the cluster, the client side hashing algorithm changes, causing a massive invalidation of the entire cache and another "thundering herd" problem at the database.
- Data Loss Assumption Failure: The team assumes data in Memcached is durable, not realizing it is a volatile, in memory store. When a server restarts, critical session data is lost.
How Axiom Cortex Evaluates Memcached Developers
Axiom Cortex is designed to find engineers who think about caching as a core architectural strategy. We test for the practical skills that are essential for building a high performance caching layer. We evaluate candidates across three critical dimensions.
Dimension 1: Caching Patterns and Strategies
This dimension tests a candidate's understanding of fundamental caching patterns.
We provide a use case and evaluate their ability to:
- Explain Caching Patterns: Can they explain the difference between cache-aside, read-through, and write-through caching?
- Design an Eviction Strategy: Do they understand that Memcached uses an LRU (Least Recently Used) eviction policy? How would they design their application around this?
- Prevent Cache Stampedes: Can they explain techniques like "stale-while-revalidate" or using a lock to prevent cache stampedes?
Dimension 2: Distributed Caching and Hashing
This dimension tests a candidate's understanding of how a Memcached cluster works.
We present a scaling problem and evaluate if they can:
- Explain Client Side Hashing: Do they understand that the logic for distributing keys across multiple Memcached servers lives in the client library?
- Understand Consistent Hashing: Can they explain why a simple modulo hashing strategy is bad and why consistent hashing is necessary to minimize cache misses when a server is added or removed?
Dimension 3: Operational Knowledge and Trade-offs
An elite developer knows the limitations of their tools.
We evaluate their knowledge of:
- Memcached vs. Redis: Can they articulate the key differences between Memcached and Redis and explain when they would choose one over the other? A high scoring candidate will talk about Memcached's simplicity and multi-threaded performance vs. Redis's data structures and persistence options.
- Monitoring: Do they know the key metrics to monitor for a Memcached cluster, such as hit rate, eviction rate, and total items?
The Foundation of a High-Performance Architecture
When you staff your team with engineers who have passed the Memcached Axiom Cortex assessment, you are investing in a team that understands how to build fast, scalable web applications. They will know how to use caching as a strategic tool to reduce database load, decrease latency, and improve user experience, forming a critical part of a modern, high performance system architecture. For complex asynchronous tasks, they might use tools like NATS or other message queues.