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From Sean Owen <so...@cloudera.com>
Subject Re: Is the RDD's Partitions determined before hand ?
Date Wed, 04 Mar 2015 09:36:50 GMT
Hm, what do you mean? You can control, to some extent, the number of
partitions when you read the data, and can repartition if needed.

You can set the default parallelism too so that it takes effect for most
ops thay create an RDD. One # of partitions is usually about right for all
work (2x or so the number of execution slots).

If you know a stage needs unusually high parallelism for example you can
repartition further for that stage.
 On Mar 4, 2015 1:50 AM, "Jeff Zhang" <zjffdu@gmail.com> wrote:

> Thanks Sean.
>
> But if the partitions of RDD is determined before hand, it would not be
> flexible to run the same program on the different dataset. Although for the
> first stage the partitions can be determined by the input data set, for the
> intermediate stage it is not possible. Users have to create policy to
> repartition or coalesce based on the data set size.
>
>
> On Tue, Mar 3, 2015 at 6:29 PM, Sean Owen <sowen@cloudera.com> wrote:
>
>> An RDD has a certain fixed number of partitions, yes. You can't change
>> an RDD. You can repartition() or coalese() and RDD to make a new one
>> with a different number of RDDs, possibly requiring a shuffle.
>>
>> On Tue, Mar 3, 2015 at 10:21 AM, Jeff Zhang <zjffdu@gmail.com> wrote:
>> > I mean is it possible to change the partition number at runtime. Thanks
>> >
>> >
>> > --
>> > Best Regards
>> >
>> > Jeff Zhang
>>
>
>
>
> --
> Best Regards
>
> Jeff Zhang
>

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