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Top 50 legacy systems Interview Questions

The most frequently asked legacy systems questions across all roles and companies, ranked by real interview frequency. Updated daily.

50questions
~7htotal time
144companies covered
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1
Behavioral & LeadershipStart here. 14 questions · ~122 min
Debugging an Undocumented Legacy SystemMedium
Recently asked

Tests ownership and problem-solving under ambiguity in a poorly documented legacy system, including how the candidate leaves lasting improvements behind.

legacy systemsDebuggingdocumentationFluencyCity Of Englewood ColoradoPPoly-Med
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2
System Design12 questions · ~104 min
Design ML Architecture for Legacy DataMedium

Design an ML data architecture that works with legacy systems while supporting scalable training, serving, and monitoring in production.

scalable architecturelegacy systemsdata architectureTEKsystemsDXC TechnologyOliver Wyman
Digital Transformation for Mission-Critical LegacyHard

Plan a data-driven transformation of mission-critical legacy systems across architecture, migration sequencing, governance, and operational risk.

enterprise architectureDigital Transformationlegacy systemsMicrosoft
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3
Pipelines4 questions · ~35 min
Real-Time Ingestion From LegacyHard

Tests your ability to design robust real-time ingestion pipelines under legacy constraints.

pipeline designlegacy systemsreal-time dataCloser Consulting
Scalable Data Ingestion PipelineMedium

Tests your ability to design robust ingestion architectures under legacy constraints.

scalabilitylegacy systemsdata ingestionQuantumBlack
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4
Execution7 questions · ~61 min
Re-architecting with 99.9% UptimeHard

Tests execution planning, risk management, and reliability engineering during large-scale service changes.

system designlegacy systemsThumbtack
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5
Strategy6 questions · ~52 min
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6
More topics7 questions · ~61 min
Optimizing a Legacy Code PathEasy
Practice

Replace an O(n²) legacy duplicate-filtering path with an order-preserving O(n) hash-set solution.

deduplicationArraysperformanceQXO
JSON Parsing, Validation, TransformationHard
Practice

Validate and normalize legacy monitoring events using schema checks, field transformation, and hash-based duplicate detection.

json parsinglegacy systemsDataBank Holdings
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Hands-on SQL practiceWrite and run real queries in the editor. 3 drills · ~30 min
SQL Duplicate Record DetectionEasy
Practice
Practice drill

Find duplicate American Institutes for Research assessment submissions using a CTE, GROUP BY, HAVING, and joins.

deduplicationsqldata integrityAmerican Institutes for ResearchPublix Super MarketsMacy's
SQL Duplicate Record CleanupMedium
Practice
Recently asked
Practice drill

Identify duplicate transaction rows, retain the earliest record, and delete later duplicates safely.

deduplicationdata cleaningtransactionsOracleDiscoverMicrosoft
Mitigate Data Skew in JoinsHard
Practice
Recently asked
Practice drill

Detect a heavily skewed join key and produce a deterministically salted join result for more balanced large-scale processing.

database optimizationlarge datasetsJoinsDatabricks
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