1. Real-Time Analytical Stores intermediate Multiple choice

    A team proposes a specialised real-time analytics store for an internal dashboard used by twelve analysts. Assess.

    2 min answer architecturecostdecision
  2. Real-Time Analytical Stores advanced Multiple choice

    A telemetry product must answer arbitrary filtered queries over hundreds of billions of events retained for 15 months, with sub-10-second response for the last 24 hours. Each event has 40 to 200 fields and cardinality is unbounded. Which storage design fits?

    3 min answer datadoghuskycolumnarobject storage
  3. Rebuild vs Re-architect advanced

    A 15-year-old system is unmaintainable. The team wants a full rewrite. What do you advise?

    2 min answer modernizationriskdecision
  4. Rebuild vs Re-architect advanced

    A platform's core system cannot support a capability the business needs. The team proposes a rebuild. What must be true for rebuild to beat incremental re-architecture?

    2 min answer rebuildrewriteincrementalrisk
  5. Rebuild vs Re-architect advanced

    An organisation running Kafka at trillions of messages per day concludes the coordination and rebalancing model no longer fits and builds a replacement. What evidence should exist before replacing a proven system rather than tuning it?

    3 min answer linkedinkafkanorthguardreplacement
  6. Rebuild vs Re-architect intermediate

    Review this plan. Eighteen months to rebuild the policy engine. Feature parity is required before any traffic moves. The legacy team is frozen to bug fixes only so that no effort is wasted on code that will be thrown away. What would you remove, what would you change, and what would you leave alone?

    3 min answer rewritefeature-parityarchitecture-reviewincremental-migration
  7. Rebuild vs Re-architect advanced

    YouTube's database team was running a growing fleet of MySQL instances with sharding logic spread through application code. Rather than replace MySQL or rewrite the application, they built Vitess as a routing tier between the two, open-sourcing it in 2011; it graduated in the CNCF in 2019. What did that choice buy, what did it cost, and where would copying it be a mistake?

    3 min answer youtubevitessshardingproxy layer
  8. Records Retention & Legal Hold beginner

    A policy says customer records are deleted seven years after the relationship ends. A team implements it literally and still fails the audit. What actually starts the clock, and what does that force into the design?

    2 min answer retentiondeletionobject-lockcrypto-shredding
  9. Records Retention & Legal Hold advanced

    A regulated fintech must prove every customer-facing balance can be reconstructed from an audit trail. Compare event sourcing, CDC into an immutable log, and conventional tables with a triggered audit log.

    3 min answer nubankevent-sourcingcdcaudit
  10. Records Retention & Legal Hold advanced

    Interview. Litigation requires you to preserve and produce every message relating to one counterparty over the last four years. Most of those conversations are in Slack and in two other SaaS tools you do not operate. Walk me through what you would show counsel in week one, and what you would have had to build beforehand.

    3 min answer legal holdslacksaasediscovery
  11. Records Retention & Legal Hold advanced

    Litigation requires preserving all records relating to a matter, overriding normal retention. How is that implemented?

    2 min answer legal-holdretentionpreservationdiscovery
  12. Records Retention & Legal Hold intermediate

    Litigation requires preserving every record relating to one counterparty, overriding a retention policy that deletes after seven years. The data sits in a 400 TB object-store data lake, roughly 60,000 Parquet files, and the relevant rows are perhaps 3% of them spread across most files. Estimate the cost of implementing the hold, and say what you would do.

    3 min answer legal-holdobject-storagetable-formatsretention