Moderate Idempotency Question 106 of 226

How do you make a POST /orders API safe to retry after a gateway timeout?

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

Without indexScan every row

With indexJump to keys

CostWrites slower

The client sends a unique Idempotency-Key

Why interviewers care about Idempotency:

This is a process

question about Idempotency.

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.

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

1
The client sends a
unique Idempotency-Key
2
the server stores the
key with the response or order id.
3
A second POST with
the same key returns the original result instead of inserting again.
4
Expire keys after a
window and uniqueness-constrain the key in the database.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

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

Say this line

“A second POST with the same key returns the original result instead of inserting”

Break into beats

AsecondPOSTwiththesame

Speaking order

2987408337471632900

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

The client sends a unique Idempotency-Key the server stores the key with the response or order id.