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Changing hash function in Hash-Join

+2 votes

In the Hash-Join algorithm we learned in lecture 13 (Query Execution- slide 25), we change the hash function in case one of the partitions is bigger than M-2 (when M is the memory size).

My question is, if the partition reached M-2 in size, it might be because all the attributes hashed are equal and hence would result in the same partition for every hash function we choose.

Is this an edge-case which we should disregard for its likelihood or am I missing something here?



asked Feb 3, 2018 by odednavon (350 points)
Good point!
I think it's an edge case you don't need to consider
(In the past exams I saw, they always tell you to assume hash join is performed without the need to repeat the partitioning to buckets).
But better confirm with Amit.

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