What is data skewness?
💡 Model Answer
Data skewness refers to an uneven distribution of data across keys or partitions in a distributed system. When a few keys contain a disproportionately large number of records, those partitions become hotspots, causing some tasks to finish much later than others. This imbalance leads to longer job runtimes and can exhaust executor resources. For example, if a user ID appears in 90% of the records, the partition handling that ID will be overloaded while others remain idle. Skew can be mitigated by redistributing data, salting keys, or using specialized join strategies like broadcast join for the small side.
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