hadoop-common-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Nick Cen <cenyo...@gmail.com>
Subject Re: Reduce doesn't start until map finishes
Date Wed, 04 Mar 2009 03:24:26 GMT
can you provide more info about sortint? The sort is happend on the whole
data set, or just on the specified partion?

2009/3/4 Mikhail Yakshin <greycat.na.kor@gmail.com>

> On Wed, Mar 4, 2009 at 2:09 AM, Chris Douglas wrote:
> > This is normal behavior. The Reducer is guaranteed to receive all the
> > results for its partition in sorted order. No reduce can start until all
> the
> > maps are completed, since any running map could emit a result that would
> > violate the order for the results it currently has. -C
>
> _Reducers_ usually start almost immediately and start downloading data
> emitted by mappers as they go. This is their first phase. Their second
> phase can start only after completion of all mappers. In their second
> phase, they're sorting received data, and in their third phase they're
> doing real reduction.
>
> --
> WBR, Mikhail Yakshin
>



-- 
http://daily.appspot.com/food/

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message