What is a Data Engineer?

A Data Engineer builds the reliable, scalable data foundations that power how products are discovered, feeds are ranked, sellers grow, and fraud is mitigated. At a marketplace like Poshmark, you translate raw behavioral events, catalog updates, payments, and social interactions into accurate, timely datasets that downstream teams depend on. Your work enables everything from relevance and recommendations to growth analytics, inventory intelligence, and operational reporting.

You will design and operate end‑to‑end data pipelines—batch and streaming—that ingest at scale, model for usability, and surface data with guarantees on freshness, quality, and cost. Expect to collaborate closely with Search & Recommendations, Product Analytics, Marketplace Operations, Trust & Safety, and Data Science to unlock new product experiences (e.g., personalized feeds) and business decisions (e.g., seller lifecycle insights). This role is critical because the marketplace’s velocity requires data systems that are both flexible and resilient, with clear ownership, observability, and SLAs.

What makes this role compelling is the breadth: one day you may optimize a Spark job’s shuffle strategy; the next you’ll design a lakehouse schema for scalable analytics, implement CDC ingestion for core entities, or define data quality contracts that protect downstream ML features. The impact is visible—clean, discoverable data improves buyer journeys, seller success, and the efficiency of every function that relies on truth in data.

Getting Ready for Your Interviews

Your preparation should center on three pillars: core coding and SQL fluency, data modeling and pipeline design, and communication under ambiguity. Interviews will mix hands-on problem solving with design conversations and structured behavioral questions. Practice moving from requirements to a pragmatic, production-ready solution with clear trade-offs.

• Role-related Knowledge (Technical/Domain Skills) – Interviewers will probe your mastery of data systems: SQL depth, distributed processing (e.g., Spark), streaming fundamentals, and data warehousing practices. Demonstrate crisp understanding of partitioning, indexing, skew handling, late data, and data quality. Show how you apply these to real production problems with metrics and outcomes.
• Problem-Solving Ability (Approach & Rigor) – Expect open-ended design prompts and algorithmic exercises. Interviewers look for systematic thinking: clarifying assumptions, proposing alternatives, analyzing complexity, and iterating toward optimal. Narrate trade-offs (latency vs. cost, throughput vs. correctness) and validate with back-of-the-envelope estimates.
• Leadership (Ownership & Influence) – You’ll be evaluated on how you define standards, improve reliability, and align cross-functional stakeholders. Highlight moments you led incident response, rolled out platform migrations, or drove schema governance. Show how you persuade through data, documentation, and empathy.
• Culture Fit (Collaboration & Ambiguity) – Poshmark values collaborative builders who communicate clearly and thrive in evolving contexts. Demonstrate curiosity, humility, and user orientation. Share examples of partnering with data scientists/engineers to co-design interfaces, SLAs, and development workflows.

Interview Process Overview

The Poshmark Data Engineer interview experience blends practical engineering depth with collaborative problem solving. You’ll encounter a pace that is respectful yet rigorous: a coding screen to validate fundamentals, followed by conversations that explore your data architecture judgment, SQL fluency, and how you operate within teams. Expect a consistent bar across interviewers, with an emphasis on clarity of thought and production relevance.

Interviewers often start by grounding the problem in real marketplace scenarios (event ingestion, feature pipelines, reporting artifacts) and then assess how you reason about scale, correctness, and maintainability. The tone is professional and candid; you’ll get space to ask questions and to iterate. Strong candidates keep solutions simple, justify decisions, and translate requirements into measurable SLAs.

This timeline illustrates the typical progression from an initial online coding assessment into a multi-conversation onsite (or virtual onsite) covering coding, SQL, design, and behavioral competencies, followed by hiring manager and senior leader discussions. Use the early rounds to calibrate expectations and clarify constraints; use the later rounds to demonstrate ownership and cross-functional leadership.

Deep Dive into Evaluation Areas

Coding & Data Structures

This area validates your ability to write clean, correct code under time constraints. Problems are practical but expect classic algorithmics to ensure you can reason about performance and edge cases. Interviewers value working solutions with clear complexity analysis and incremental optimization.

• Be ready to go over:
  • Arrays/Strings: hashing, two-pointers, sorting, permutations
  • Linked Lists: pointer manipulation, kth-from-end
  • Stacks/Monotonic Structures: next-greater element patterns
  • Trees/Graphs: traversal strategies, vertical ordering, BST transformations
  • Advanced concepts (less common): in-place data structure design, amortized analysis, custom collection implementations
• Example questions or scenarios:
  • "Group anagrams and discuss O(n), O(n log n), and space trade-offs"
  • "Find the kth element from the end of a linked list—single pass vs. two pass"
  • "Next greater element in an array—optimize with a monotonic stack"
  • "Implement an ArrayList using a fixed array—growth strategy and amortized costs"
  • "Transform a BST to replace each node with the sum of greater nodes (reverse in-order)"

SQL & Data Manipulation

Your SQL depth signals whether you can transform raw tables into reliable, performant datasets. Expect tasks involving joins, window functions, aggregations, and careful handling of duplicates and nulls. Interviewers will ask about query plans and how you optimize for scale.

• Be ready to go over:
  • Window functions: rank, dense_rank, lag/lead for feature building and report metrics
  • Join strategies: inner vs. left, semi/anti joins, handling many-to-many explosions
  • Data quality: deduplication using window specs, surrogate keys, idempotent upserts
  • Advanced concepts (less common): partition pruning, clustering/z-ordering, incremental models and CDC merges
• Example questions or scenarios:
  • "Given events with duplicates, produce session-level metrics with deterministic dedupe"
  • "Compute daily active sellers with rolling 7/28-day cohorts using windows"
  • "Explain how you’d optimize a slow join on large dimension tables"
  • "Design a SQL model that supports both daily aggregates and ad-hoc drill-down"

Data Modeling & Warehousing

Here you translate business domains into schemas that scale. You’ll discuss entities, relationships, slowly changing dimensions, and modeling for analytics and ML feature stores. Clear naming, lineage, and governance matter.

• Be ready to go over:
  • Dimensional modeling: star/snowflake, fact grain, surrogate keys
  • SCD patterns: Type 1 vs. Type 2 and when to use each
  • Feature pipelines: offline/online consistency, point-in-time correctness
  • Advanced concepts (less common): data contracts, schema evolution, lakehouse layouts, time travel/versioning
• Example questions or scenarios:
  • "Model buyers, sellers, listings, and orders for marketplace analytics"
  • "Design a schema for a recommendations feature store ensuring no data leakage"
  • "Handle schema changes to a core events table without breaking downstream jobs"

Distributed Processing & Streaming

This assesses your grasp of systems like Spark, Flink, Kafka, or similar. You’ll reason about throughput, latency, state management, and exactly-once semantics. The goal is to show you can deliver reliable pipelines under real load.

• Be ready to go over:
  • Batch processing: partitioning, skew mitigation, shuffle optimization, checkpointing
  • Streaming: consumer groups, backpressure, windowing, watermarking, late data handling
  • Reliability: idempotency, dedupe strategies, transactional sinks
  • Advanced concepts (less common): state stores, compacted topics, outbox/CDC patterns, lakehouse streaming sinks
• Example questions or scenarios:
  • "Design a clickstream ingestion pipeline with near real-time aggregations and SLAs"
  • "Handle late-arriving events with correctness guarantees"
  • "Optimize a skewed Spark job where a hot key dominates traffic"

System Design for Data Platforms

Expect open-ended design prompts focused on end-to-end data delivery: ingestion, storage, processing, serving, cost, and observability. Interviewers want clear interfaces, SLAs, and a stepwise plan to iterate.

• Be ready to go over:
  • Ingestion: batch vs. streaming trade-offs, CDC vs. full loads
  • Storage: lake vs. warehouse choices, file formats (Parquet), partitioning
  • Serving: marts, semantic layers, contracts for DS/analytics
  • Advanced concepts (less common): multi-tenant isolation, cost governance, metadata/lineage, RBAC/PII handling
• Example questions or scenarios:
  • "Design the data backbone for a ‘Recommended Listings’ feature—from raw events to serving layer"
  • "Build a deduplicated, privacy-aware profile data pipeline with GDPR deletion support"
  • "Create a data quality framework with SLIs/SLOs and alerting"

Use this visualization to spot hot topics and repeated themes across interviews (e.g., arrays/strings, SQL windows, Spark, streaming, and data modeling). Prioritize practice on the largest terms, then shore up secondary areas to avoid gaps across the onsite.

Key Responsibilities

You will own mission-critical pipelines and datasets that serve product, analytics, and ML. This includes designing new data flows, hardening existing ones, and partnering with stakeholders to define contracts and SLAs. You’ll drive best practices in data modeling, testing, and observability to raise the engineering bar.

• Build and operate batch and streaming pipelines from ingestion to serving, with clear recovery and backfill strategies.
• Design analytical and feature schemas that are discoverable, documented, and evolution-friendly.
• Implement data quality checks, lineage, and monitoring; respond to and prevent incidents.
• Collaborate with Data Science, Analytics, and Product to translate requirements into scalable technical plans.
• Optimize for performance and cost across compute, storage, and access patterns.
• Contribute to platform tooling (e.g., CI/CD for data, orchestration patterns, shared libraries) to improve team velocity.

Day to day, you’ll review PRs, iterate on DAGs, tune jobs, meet with partners to shape requirements, and proactively improve the reliability and clarity of the data ecosystem.

Role Requirements & Qualifications

Successful candidates combine deep technical skills with pragmatism and ownership. You should be comfortable taking ambiguous requirements and delivering robust, maintainable solutions that scale with the business.

• Must-have technical skills:
  • Strong SQL with comfort in complex joins, window functions, and performance tuning
  • Proficiency in a general-purpose language (e.g., Python, Java, or Scala) for data engineering
  • Experience with distributed processing (e.g., Spark) and orchestration (e.g., Airflow)
  • Knowledge of data modeling (dimensional design, SCD), file formats (Parquet), and partitioning
  • Understanding of streaming concepts (Kafka-like systems, windows, watermarking) and idempotent sinks
• Nice-to-have technical skills:
  • Experience with lakehouse/warehouse platforms and CDC ingestion
  • Familiarity with data quality frameworks, lineage, and governance practices
  • Exposure to feature stores and ML data patterns
• Experience and background:
  • Prior ownership of production pipelines with measurable SLAs and on-call participation
  • Collaboration with cross-functional partners (DS, analytics, product) and documented data contracts
• Soft skills that set you apart:
  • Clear written communication, pragmatic trade-off thinking, and bias for iteration
  • Leadership through influence: standards, mentoring, and incident retros

This module summarizes current compensation trends for Data Engineers, including base salary ranges and typical bonus/equity components. Use it to calibrate expectations by level and location; remember that final offers reflect experience, impact, and market conditions.

Common Interview Questions

Expect a mix of practical coding, SQL, design, and behavioral questions. The examples below reflect real patterns from prior Poshmark Data Engineer interviews and closely related roles.

Coding & Data Structures

Covers correctness, complexity, and clarity under time pressure.

• Group anagrams; discuss O(n log n) vs. O(n) hashing trade-offs
• Kth element from the end of a linked list (single pass with two pointers)
• Next greater element in an array (monotonic stack)
• Most frequent elements in an array in O(n) time (heap vs. hashmap + bucket)
• Next greater permutation of digits (in-place algorithm)
• Vertical order traversal of a binary tree
• Replace each BST node with the sum of greater nodes (reverse in-order)
• Implement an ArrayList using arrays; explain resizing and amortized cost

SQL & Data Processing

Focuses on windows, joins, dedupe, and performance.

• Write a query to dedupe click events and compute session metrics
• Calculate rolling 7/28-day active users with window functions
• Diagnose a slow join and improve it (keys, distribution, partitioning)
• Build a daily incremental model with late-arriving data
• Design an idempotent upsert (MERGE) pattern for CDC

System Design & Pipelines

Evaluates architecture judgment and trade-offs.

• Design a streaming ingestion pipeline for marketplace events with exactly-once sinks
• Build an end-to-end pipeline for recommendations features with online/offline consistency
• Create a data quality framework with SLIs, SLOs, and alerting
• Architect a warehouse/lakehouse layout for analytics and ML

Behavioral & Leadership

Explores ownership, collaboration, and learning.

• Tell me about a time you stabilized a flaky pipeline and prevented regression
• Describe a challenging cross-team dependency and how you aligned on a contract
• Walk through an incident you led: detection, impact, fix, and prevention
• Share an example of mentoring or raising standards on your team

Problem-Solving / Case Studies

Assesses structured thinking under ambiguity.

• Given ambiguous product metrics, propose definitions, data sources, and validation
• Estimate scale/cost for a new pipeline and propose an MVP plan with metrics
• Evaluate build vs. buy for a streaming component (e.g., CDC, schema registry)

These questions are based on real interview experiences from candidates who interviewed at this company. You can practice answering them interactively on Dataford to better prepare for your interview.

Frequently Asked Questions

Q: How difficult is the interview and how long should I prepare?
Expect medium rigor with a strong emphasis on fundamentals. Most candidates benefit from 2–4 weeks of focused practice on coding, SQL, and data design, plus a few mock sessions to refine communication.

Q: What makes successful candidates stand out?
Clarity and pragmatism. Top performers build correct solutions quickly, explain trade-offs with data, and show ownership of production-quality systems (testing, observability, cost).

Q: How structured is the interview process?
It is organized and respectful, usually starting with an online assessment followed by multiple technical and behavioral conversations. Timelines can vary; communicate constraints and ask about scheduling if you have deadlines.

Q: What’s the culture like for Data Engineers?
Collaborative and product-oriented. You’ll partner closely with DS/analytics and are expected to advocate for data quality, clear contracts, and sustainable delivery.

Q: Are roles location-flexible or remote?
Availability varies by team and location. Clarify preferences with your recruiter early; hybrid arrangements are common for data teams, subject to business needs.

Other General Tips

• Lead with structure: State assumptions, outline your approach, then implement. Interviewers reward visible, methodical thinking.
• Narrate complexity: Always provide time/space complexity and discuss bottlenecks; propose optimizations if time permits.
• Design with SLAs: In system rounds, anchor decisions to freshness, latency, availability, and cost targets to show production mindset.
• Instrument your solutions: Mention how you’d test, observe, and alert on pipelines—this signals real-world readiness.
• Ask targeted questions: Clarify data volumes, update patterns, and consumers; it shows you’re optimizing for context, not theory.
• Show iteration: Present a minimal viable design, then layer enhancements (e.g., quality checks, schema registry, backfills).

Summary & Next Steps

As a Data Engineer, you will power Poshmark’s marketplace with trustworthy, timely data that elevates search, recommendations, fraud prevention, and analytics. The role blends hands-on building with system-level design and cross-functional collaboration—work that directly influences buyer and seller success.

Focus your preparation on three fronts: coding and SQL fundamentals, data modeling and pipeline/system design, and clear, structured communication. Practice with real interview-style problems (arrays/strings, linked lists, trees; SQL windows and joins), rehearse architecture narratives anchored to SLAs, and prepare concise stories that demonstrate ownership and impact.

You’re now equipped with a clear roadmap. Dive into focused practice, run a few mock interviews, and calibrate your expectations with the compensation and process insights provided here. Explore more insights on Dataford to refine your plan. Step into your interviews with confidence—your ability to build reliable data systems can create outsized impact for the marketplace and its community.