Q: Consistent hashing vs rendezvous (HRW) hashing — which for what scale?

**Target Audience:** Readers who know the basic hash ring and virtual nodes; see [What is consistent hashing?](/interview-question/what-is-consistent-hashing) and [What is consistent hashing with virtual nodes and when do you need it?](/interview-question/what-is-consistent-hashing-with-virtual-nodes-and-when-do-you-need-it) if not. **Difficulty:** Hard **Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). History is cited from Thaler and Ravishankar

Question 1

What is consistent hashing with virtual nodes and when do you need it?

Accepted Answer

**Target Audience:** Readers who know the basic hash ring; if you do not, read [What is consistent hashing?](/interview-question/what-is-consistent-hashing) first, as this page builds on it.
**Difficulty:** Medium
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). Cassandra facts are cited from The Last Pickle, Instaclustr and the Apache Cassandra 4.0 production docs.

> **How to read this doc:** Every idea is explained in plain language first, the

Question 2

What is consistent hashing?

Accepted Answer

**Target Audience:** Beginners to system design who know what a hash function and a cache are; no distributed-systems background assumed.
**Difficulty:** Medium
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). History is cited from Karger et al., STOC 1997; system usage from the Dynamo paper (SOSP 2007) and the Apache Cassandra documentation.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interv

Question 3

How would you design a distributed key-value store / query cache for search?

Accepted Answer

## Step 1: Use Cases, Constraints, Assumptions, Back-of-Envelope

### Use cases
We'll scope to handle only the core flows that expose the bottlenecks; everything else is deferred.

- **User** searches — GET `/search?q=...`, cache lookup by normalized query hash, hit returns in <20ms, miss fetches search tier.
- **Service** caches query results — write-through on miss with TTL + jitter, LRU eviction, per-tenant isolation.
- **Service** invalidates — TTL expiry plus explicit invalidation on index

Question 4

Consistent hashing vs rendezvous (HRW) hashing — which for what scale?

Accepted Answer

**Target Audience:** Readers who know the basic hash ring and virtual nodes; see [What is consistent hashing?](/interview-question/what-is-consistent-hashing) and [What is consistent hashing with virtual nodes and when do you need it?](/interview-question/what-is-consistent-hashing-with-virtual-nodes-and-when-do-you-need-it) if not.
**Difficulty:** Hard
**Verified with:** Node 22.22, Python 3.12, Go 1.24 and Java 21 (all four print identical output). History is cited from Thaler and Ravishankar

SYSTEM DESIGNDECODED.

Medium

What is consistent hashing with virtual nodes and when do you need it?

What is consistent hashing?

Hard

How would you design a distributed key-value store / query cache for search?

Consistent hashing vs rendezvous (HRW) hashing — which for what scale?