Question 1

Tell me about yourself and your experience.

Accepted Answer

**Situation**: I joined the data org when our pipelines were monolithic, causing 4+ hour delays and frequent outages affecting downstream dashboards and ML models.

**Task**: I was tasked with redesigning the data platform to support real-time decisioning while improving reliability and cost efficiency.

**Action**: I led a cross-functional team of 5 engineers to architect a medallion (Bronze/Silver/Gold) architecture on Delta Lake....

Question 2

Explain the differences between a Data Lake and a Data Warehouse.

Accepted Answer

**Data Lake**: Low-cost object storage (S3, ADLS) for raw, semi-structured, unstructured data. Schema-on-read; used for exploratory analytics, ML, archival. **Data Warehouse**: Structured, curated storage optimized for SQL; schema-on-write; used for BI and reporting. **Why both exist**: Lakes offer flexibility and cost at scale; warehouses offer query performance and concurrency....

Question 3

What is the difference between OLTP and OLAP?

Accepted Answer

**Architectural Logic:** OLTP optimizes for transactional throughput (high-frequency, small, ACID reads/writes); OLAP for analytical throughput (complex aggregations, scans, read-heavy). **Why separate:** Schema and indexing are opposites—OLTP uses narrow indexes and normalization; OLAP uses columnar storage and denormalized star schemas. **Scalability:** OLTP scales vertically and via sharding; OLAP scales horizontally via MPP (e.g., Snowflake, BigQuery, Redshift)....

Question 4

What challenges did you face during these projects?

Accepted Answer

Situation: Project challenges. Task: Reflect with resolution. Action: Integration complexity, data quality, performance, stakeholder alignment, documentation. Addressed with incremental delivery, testing, data council, runbooks....

Question 5

Describe an AWS EC2 instance and how IAM roles/policies enhance security.

Accepted Answer

Architectural logic: EC2 = compute; IAM roles = identity without long-lived keys. Why roles matter: Embedded access keys are a top breach vector; roles use instance metadata for temporary credentials that rotate automatically. Flow: Attach role at launch → app uses default credential chain (boto3, SDK) → no keys in code. Policies define S3, Secrets Manager, etc. Scalability: One role can serve many instances; policies scale via JSON. Cost: No extra cost for roles....

Question 6

Discuss S3's advantages, including scalability and durability.

Accepted Answer

Architectural logic: S3 is object storage with 11 nines durability, multi-AZ by default. Scalability: Virtually unlimited; no capacity planning. Cost: Pay per GB; lifecycle for tiering. Why it matters for data lakes: Decoupled from compute; native integration (Glue, Athena, EMR). Trade-offs: Eventual consistency for overwrites (rare); no POSIX—use prefixes, not directories....

Question 7

Explain the recent projects you have worked on.

Accepted Answer

**Situation**: Recent work spans real-time analytics, lake migration, ML features.

**Projects**: (1) Real-time platform—Kafka, Flink, ClickHouse; (2) Lake migration—on-prem Hadoop to S3+Spark; schema evolution; (3) ML feature pipelines—batch + stream for recommendations.

**Result**: 50% latency reduction; 30% cost savings. Focus on reliability, observability, maintainability....

Question 8

What is currying in Scala?

Accepted Answer

Currying: Multi-arg function → chain of single-arg functions. def add(a:Int)(b:Int)=a+b; val add5=add(5)_; add5(3)=8. Use: partial application, DI, configuration. Example: def connect(host:String)(port:Int); val local=connect('localhost')_.

Question 9

Write a Python function to reverse all strings in a list.

Accepted Answer

**One-Liner:** [s[::-1] for s in lst]. [::-1] is slice for reverse. Handle None: [s[::-1] if s else s for s in lst].

**Production:** For DataFrame: df['col'] = df['col'].str[::-1]. Used for reversing IDs, fixing reversed dates....

Question 10

Write a higher-order function to filter values greater than a threshold in a list.

Accepted Answer

**Higher-Order:** Returns or accepts functions. filter_above(10) returns lambda x: x>10. Composable: pipe multiple filters.

def filter_above(threshold):
    return lambda x: x > threshold
list(filter(filter_above(10), nums))
# Or: from functools import partial; filter_gt10 = partial(filter, lambda x: x>10)

Chryselys Data Engineer Interview Questions

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Chryselys Data Engineer Interview Questions

Companies asking these questions

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More Interview Prep Guides

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