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Hive >> mail # user >> Partition performance

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Re: Partition performance
On 2 Jul 2013, at 16:51, Owen O'Malley wrote:

> On Tue, Jul 2, 2013 at 2:34 AM, Peter Marron <
>> Hi Owen,****
>> ** **
>> I’m curious about this advice about partitioning. Is there some
>> fundamental reason why Hive****
>> is slow when the number of partitions is 10,000 rather than 1,000?
> The precise numbers don't matter. I wanted to give people a ballpark range
> that they should be looking at. Most tables at 1000 partitions won't cause
> big slow downs, but the cost scales with the number of partitions. By the
> time you are at 10,000 the cost is noticeable. I have one customer who has
> a table with 1.2 million partitions. That causes a lot of slow downs.

That is still not really answering the question, which is: why is it slower
to run a query on a heavily partitioned table than it is on the same number
of files in a less heavily partitioned table.