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What people report studying for — not a take-home dump. Last editorial update 2026-08-22.
Rounds you should expect
Streaming
Consumer groups, rebalances, and why compaction is wrong on an event topic.
SQL
A feed metric that must not double-count impressions after a join to a member dimension.
Recently added questions
2026-08-22 · Rebalances under load
Your consumer group rebalances every few minutes during peak. What do you check first?
max.poll.interval.ms vs processing time, cooperative sticky assignment, and whether a slow partition (hot key) is triggering leave/join. Adding consumers without fixing poll interval often makes lag worse.
From the question bank
hard · SQL · SQL
When do you use a covering index / clustering key versus rewriting the query?
Practice →easy · Warehouse · Databricks
A shuffle-heavy join OOMs the worker. Name three levers before you “just scale the cluster.”
Practice →easy · Streaming · Kafka
Why can two consumers in the same group not share one partition?
Practice →easy · Streaming · Kafka
Compaction vs deletion retention. When do you use a compacted topic?
Practice →easy · Streaming · Kafka
max.poll.interval vs a slow sink.
Practice →hard · Streaming · Kafka
linger.ms and batch.size — what are you trading?
Practice →medium · Streaming · Kafka
Schema registry compatibility in CI.
Practice →hard · Streaming · Kafka
acks=all and a producer still duplicates. How?
Practice →medium · Streaming · Kafka
Schema Registry BACKWARD vs FULL. What can a producer do on Monday?
Practice →easy · Coding · Spark
Narrow vs wide transformation. Why does that decide runtime?
Practice →easy · Coding · Spark
foreach on the driver vs foreachPartition.
Practice →hard · System design · System design
Exactly-once from Kafka into a warehouse. What do you actually promise?
Practice →