InterviewsVector
AdvancedPrincipalData Architecture & Consistency65 minutesPro answer

SDV-015

Partition high-cardinality entities when the hottest keys keep changing

Design adaptive placement for a workload whose skew shifts faster than manual shard maps, without sacrificing local invariants or creating unbounded movement.

Capacity Planning10x ScaleConsistencyData Migration

Interview prompt

Problem context

A metrics platform stores billions of series. Most are cold, but customer launches make arbitrary series hot within minutes. Hash partitioning balances count, not write intensity, and range partitioning creates hotspots. Queries need recent per-series order and tenant-level scans.

Skills being evaluated

skew analysisadaptive partitioninghot-key mitigationquery trade-offs

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What the full guide covers

Clarify the decision
Establish scale assumptions
Functional and non-functional requirements
High-level architecture
Data model and flow
Consistency and transaction boundaries
Failure modes and recovery
Security and privacy
Observability and SLOs
Capacity and cost
Alternatives and trade-offs
Evolution and migration
What Staff and Principal candidates should emphasize

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Protect latency SLOs from scans, compaction, and background work using admission, pools, replicas, workload contracts, and resource accounting.

Senior · 55 min

Migrate a multi-terabyte database without downtime or wishful dual writes

Plan snapshot, change capture, validation, cutover, rollback, and cleanup for a live database whose write rate and long tail make naïve copying unsafe.