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How do you monitor and debug skewed partitions?

SQLmedium0.3 min readPremium
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
TCS
Key Concepts Tested
joinpartitionspark
Expert AnswerPremium
56 wordsInterview-ready
**Monitor**: Spark UI—task duration distribution; stragglers indicate skew. **Profile**: df.rdd.mapPartitions(lambda it: [sum(1 for _ in it)]).collect() for partition sizes. **Identify**: Skewed keys (e.g., NULL, default values). **Fix**: (1) Salting: add random suffix to key; join; aggregate. (2) Broadcast small side. (3) Two-phase aggregation. (4) AQE skew join (Spark 3.x)....
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