High Caching Question 182 of 226

How does consistent hashing help when you add a Redis node to a cache cluster?

Java Specialist · Speak this in 60–90 seconds · Faridabad & Delhi NCR

PICTURE THIS: DATABASE INDEX

Without indexScan every row

With indexJump to keys

CostWrites slower

Simple meaning

Naive modulo hashing remaps almost every key when N changes, causing a thundering miss on the database.

WHY — Caching instead of guessing?

Why interviewers care about Caching:

This is a process

question about Caching.

Panels listen for order,

trade-offs, and what you would actually do on a Backend project - not buzzwords.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

STEPS — What happens step by step?

Before you speak the answer, walk the interviewer through these steps:

1
Naive modulo hashing remaps
almost every key when N changes, causing a thundering miss on the database.
2
Consistent hashing remaps only
a fraction of keys near the new node.
3
You still need TTLs
because some keys will miss during the move.
4
Give an example
One tiny concrete case you can say aloud.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

EXAMPLE — See it in action

Here's a short line you can speak, broken into clear beats:

Say this line

“Consistent hashing remaps only a fraction of keys near the new node.”

Break into beats

Consistenthashingremapsonlyafraction

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

Key takeaway

Naive modulo hashing remaps almost every key when N changes, causing a thundering miss on the database. Consistent hashing remaps only a fraction of keys near the new node.