Got it.
Thanks for your reply.
Zhiwen Sun
On Wed, Dec 23, 2015 at 2:24 PM, Gopal Vijayaraghavan <gop...@apache.org>
wrote:
>
> > But why disable mapjoin has better performance when we don't use cast to
> >string(user always lazy)?
> >
> > Join key values comparison in in reduce stage is more quickly?
>
> The HashMap<DoubleWritable, RowContainer> is slower than the full-sort +
> sorted-merge-join.
>
>
> It shouldn't be, but it hits the worst-case performance for the Hashmap
> impl because of a bug in DoubleWritable in Hadoop.
>
> The effect is somewhat the same as
>
> public int hashCode() {
> return 1;
> }
>
> Read the comments on - https://issues.apache.org/jira/browse/HADOOP-12217
>
> Cheers,
> Gopal
>
>
>
>
>
>
>
