CODEWITHSUNDEEP
mapreducehive
user4288560
user4288560

Reputation:

When will Hive run the MapReduce?

As I have observed some times the Hive is giving the result immediately but some times it is running the MapReduce job. Just wanted to know when it will run the MapReduce job and when it will not run?

Upvotes: 0

Views: 56

Answers (1)

Amar
Amar

Reputation: 3845

Whenever you run any "select *" job, no map reduce job will be started. Whereas if you run any querying involving selecting a specific column(s) or some aggregation options, hive will invoke a map reduce operation.

The high level idea is that "select *" is simply a "cat" command kind of operation and data is just displayed back to you as it is without involving any kind of operations on it.

Upvotes: 1

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