Order by, Sort by, Distribute By, Cluster by in Hive

These four clauses provided by HIVE are very important in context of Big Data as they provide a way to achieve sorting on big datasets.

  • ORDER BY x: guarantees global ordering, but does this by pushing all data through just one reducer. This is basically unacceptable for large datasets. You end up one sorted file as output.
  • SORT BY x: orders data at each of N reducers, but each reducer can receive overlapping ranges of data. You end up with N or more sorted files with overlapping ranges.
  • DISTRIBUTE BY x: ensures each of N reducers gets non-overlapping ranges of x, but doesn’t sort the output of each reducer. You end up with N or unsorted files with non-overlapping ranges.
  • CLUSTER BY x: ensures each of N reducers gets non-overlapping ranges, then sorts by those ranges at the reducers. This gives you global ordering, and is the same as doing (DISTRIBUTE BY x and SORT BY x). You end up with N or more sorted files with non-overlapping ranges.

More detailed explanation is given here

References:
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+SortBy
http://stackoverflow.com/questions/13715044/hive-cluster-by-vs-order-by-vs-sort-by
http://stackoverflow.com/questions/13715044/hive-cluster-by-vs-order-by-vs-sort-by

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