#idempotency

12 idempotency interview questions, asked at Databricks, Microsoft, Nvidia and 7 more companies. Last asked Oct 2026.

Make a charge-then-record payment flow safe against crashes and retriesCodingA backend first charges a customer through an external payment provider and then writes the payment to its own database. You are shown code like this (in Java or Python) and asked…
Last asked Oct 2026
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Design a payment systemSystem designAccept card payments for merchants: authorize, capture, settle with card networks, and reconcile, never charging twice or losing money.
Last asked Oct 2026
Load daily LLM chat logs into a warehouse idempotentlySystem designEvery day one JSONL file of LLM conversations lands in object storage; each line is a conversation with an id, a user id, its messages and metadata. Design the job that loads it…
Last asked Sep 2026
Design a payments ledgerSystem designDesign the double-entry ledger behind a payments API: money movements must never be lost or applied twice.
Last asked Aug 2026
Design an idempotent double-entry ledger serviceSystem designDesign a ledger service that records money movements for merchants as double-entry transactions and answers balance and history queries. Cover the data model, making writes…
Last asked Aug 2026
Order service whose database write succeeds but queue publish failsSystem designDesign the order path of an online bookstore. When an order request arrives, the service inserts the order into its database and then publishes a message to a queue (Amazon SQS)…
Last asked Aug 2026
Design a reliable job schedulerSystem designDesign a service that runs jobs at scheduled times at large scale, such as payment jobs that must run on time and exactly once in effect. Cover storing schedules, finding jobs…
Last asked Aug 2026
Data platform and pipeline operations deep diveSystem designAfter a short coding warm-up, discuss running production data pipelines: streaming ingestion, metrics and alerting, idempotent reprocessing, batch jobs on Spark, and how you keep…
Last asked Jul 2026
Technical recruiter screen: duplicate requests and a streaming chat UISystem designThe first recruiter call is more technical than most. After the background questions (how much of the last year you spent writing code, whether you lean frontend, backend or full…
Last asked Apr 2026
Idempotent request handling with idempotency keysCodingImplement a request handler that uses client-supplied idempotency keys so that retrying the same request returns the original result instead of doing the work twice. Handle two…
Last asked Feb 2026
Design a digital game store backendSystem designDesign the backend of an online store that sells digital games: players browse a catalog, buy games, and own them afterwards. Focus on the purchase: taking the payment, granting…
Last asked Dec 2025
Design an artifact store on Kubernetes and CassandraSystem designA Java web API runs in Kubernetes on top of a Cassandra cluster and stores artifacts, each identified by a user-given name. An artifact must be created only once, even when…
Last asked Sep 2025