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Home/Questions/Cloud/Tools/What types of queries would not be efficient in Athena?

What types of queries would not be efficient in Athena?

Cloud/Toolshard0.4 min readPremium

**Athena economics**: $5/TB scanned—inefficient queries burn budget. **Inefficient patterns**: (1) Full table scans on unpartitioned data—always partition. (2) Many small files—each incurs metadata overhead; coalesce to 128MB+ Parquet. (3) SELECT *—scan only needed columns. (4)...

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Frequency
Low
Asked at 1 company
Category
179
questions in Cloud/Tools
Difficulty Split
104E|27M|48H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Capco
Key Concepts Tested
joinoptimizationpartition

Why This Question Matters

This hard-level Cloud/Tools question appears frequently in data engineering interviews at companies like Capco. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join, optimization, partition) will help you answer variations of this question confidently.

How to Approach This

This is a senior-level question that tests architectural thinking. Lead with the high-level design, then drill into specifics. Discuss trade-offs explicitly - there is rarely one correct answer. Show awareness of scale, fault tolerance, and operational complexity.

Expert Answer
87 words

Athena economics: $5/TB scanned—inefficient queries burn budget. Inefficient patterns: (1) Full table scans on unpartitioned data—always partition. (2) Many small files—each incurs metadata overhead; coalesce to 128MB+ Parquet. (3) SELECT *—scan only needed columns. (4) Complex joins without partition pruning—filter early. (5) Cross joins, Cartesian products. (6) UDFs on every row. (7) OLTP-style point lookups—use RDS. Why: Athena is for analytical scans; it's not a database. Optimization: Partition by date/key; Parquet/ORC; partition projection; limit columns. Cost: Unpartitioned 10 TB scan = $50/query; partitioned + filter = $5.

The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations covering performance optimization and real-world examples.

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According to DataEngPrep.tech, this is one of the most frequently asked Cloud/Tools interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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