#databases

13 databases interview questions, asked at Amazon, Apple, Databricks and 7 more companies. Last asked Sep 2026.

Cut read latency in an existing relational database designSystem designYou are shown the database design behind a real service: a relational store that has become slow to read. Propose how you would change it to bring read latency down. Start by…
Last asked Sep 2026
Rewrite a SQL query plan treeCodingA query plan is a tree of scan, filter, project and join nodes. Write rewrite rules that make it cheaper, such as moving a filter beneath a join, while the new plan still returns…
Last asked Sep 2026
Locks versus MVCC in a versioned storeCodingYou have a store that keeps versions of its data. Compare protecting concurrent readers and writers with locks against multi-version concurrency control: how each works, what…
Last asked Aug 2026
Threshold-based database partition rebalancerCodingWrite a rebalancer for database partitions spread across nodes: when a node's load goes over a threshold, move partitions off it onto other nodes. Explain which partitions you…
Last asked Jul 2026
High availability and failover for a primary-replica databaseSystem designExplain how to keep a primary-replica database available: how replication works, how a failed primary is detected, how a replica is promoted, and how you avoid losing writes or…
Last asked Jun 2026
Design an API to deep-copy a dataset with its tasks, responses and gradesSystem designA dataset holds tasks, each task holds model responses, and each response holds grades. Design an API that copies a dataset with everything under it, so that the copy and the…
Last asked May 2026
Systems fundamentals quick-fire: memory, processes, threads and transactionsCodingA short screen of basics, answered out loud: 1. What an array is, how it is laid out in memory, and how it differs from a linked list. 2. What a smart pointer is and the kinds you…
Last asked Feb 2026
Design a database that tracks changes to resourcesSystem designDesign a store that records every change to a set of resources so users can see a resource's history and its state at any past time. Cover the data model, writes, queries over…
Last asked Jan 2026
Database internals: WAL, MVCC, replication and recoveryCodingExplain the internals a relational database relies on: write-ahead logging and why it makes commits durable, multi-version concurrency control and how readers avoid blocking…
Last asked Jan 2026
Design a cloud database's write path and crash recoverySystem designDesign how writes flow through a managed cloud relational database: from a client's commit to durable storage, how the data is replicated across machines or zones, and how the…
Last asked Jan 2026
Explain ACID and transaction isolation levelsSystem designExplain what each letter of ACID guarantees, then walk through the standard isolation levels (read uncommitted, read committed, repeatable read, serializable) and the anomalies…
Last asked Dec 2025
Design a cache for query views that depend on each otherSystem designIn a data warehouse, views are defined on top of tables and other views, so the views form a DAG. Design a cache that speeds up queries over these views and keeps it correct when…
Last asked Sep 2025
Keep a shared payment account correct under concurrent paymentsSystem designTwo people share one online payment account and pay with it at the same moment. How do you make sure the balance never goes wrong? Answer from the API side (idempotency, request…
Last asked Jul 2025