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From Dmitriy Ryaboy <dvrya...@gmail.com>
Subject Re: timeseries merge/join question
Date Thu, 05 Nov 2009 17:51:58 GMT

I am not sure that the join package would work in this particular case.

The javadoc says "Given a set of sorted datasets keyed with the same
class and yielding equal partitions, it is possible to effect a join
of those datasets prior to the map" -- Calvin's datasets are not
necessarily equally partitioned.

Moreover, mapred.join assumes equijoins (equality can be modified by
providing a key comparator).  Calvin's use case is "join to the record
before the equal record" which requires more context than a Comparator
sees. Are you suggesting that one could use a custom JoinRecordReader?
I suspect even so, there is the edge problem -- if timestamps of first
records on a given partition are equal, you want to fetch the last
record of the previous partition.


On Thu, Nov 5, 2009 at 6:20 AM, Jason Venner <jason.hadoop@gmail.com> wrote:
> org.apache.hadoop.mapred.join in hadoop 19
> On Wed, Nov 4, 2009 at 10:20 AM, Dmitriy Ryaboy <dvryaboy@gmail.com> wrote:
>> > This is essentially how Pig does its skewed join, with some
>> > simplifications.
>> Um, I meant merge join :-).
> --
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