Technology Selection & Deep Technical Knowledge Questions

Deep understanding of specific technologies relevant to complex system design. Master databases (PostgreSQL, Cassandra, DynamoDB, Elasticsearch), message queues (Kafka, RabbitMQ), caching systems (Redis), search engines, and frameworks. Understand their strengths, weaknesses, trade-offs, operational characteristics, scaling patterns, and common pitfalls. Be able to justify technology choices based on specific system requirements.

MediumTechnical

42 practiced

You need low-latency prefix search and fuzzy matching for product names. Compare implementing this with Elasticsearch, Postgres trigram (pg_trgm) indexes, and a managed search service. Explain expected accuracy, scaling characteristics, and operational costs for each option.

MediumTechnical

44 practiced

Given the table:

transactions(
  transaction_id uuid PRIMARY KEY,
  user_id int,
  category_id int,
  amount numeric(12,2),
  occurred_at timestamptz
)

Write a PostgreSQL query that returns top-3 spenders per category over the last 90 days using window functions. Include handling of ties deterministically.

HardSystem Design

48 practiced

Describe how to implement cross-service transactions across microservices that use different databases without two-phase commit. Explain the Saga pattern (choreography vs orchestration), compensation actions, idempotency, and how to reason about failure recovery and observability.

EasyTechnical

39 practiced

Describe primary key selection and use of foreign keys in a relational database. Then explain how to map those relational concepts when modeling data in a NoSQL system like DynamoDB or Cassandra, highlighting trade-offs in queryability and join avoidance.

HardTechnical

44 practiced

A Cassandra cluster exhibits a hot partition caused by monotonically increasing keys (for example sequential user ids or timestamps). Propose a redesign of partition keys and data layout to avoid hotspots while keeping query complexity low and minimizing data duplication. Include migration and backfill considerations.

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