Hi, the framework doesn't give you the first/last information about reduce job you perform in your reducer. Just as the mapper doesn't give you information whether the (key, value) pair passed to map function is first/last for a given key. However you can workaround this by adding special values to your data, e.g. <page><id>0</id>... and <page><id>Long.MAX_VALUE</id>.... When you encounter those in your reducer, you know you are at the beginning/end of your data and you can emit <root> and </root>.
Regards, Pawel 2010/10/21 Johannes.Lichtenberger <[email protected]>: > Hi, > > is it possible to reverse the sort-order? I mean, it seems the reducers > are getting the output in descending order. As I want to sort wikipedia > revisions of articles it would be great in ascending order. Now the > output on a simple little test file is (sorted/grouped automatically by > Map/Reduce): > > <page><id>774932</id><title>foo</title><revision><id>89865</id><timestamp>2003-11-21T02:12:21Z</timestamp><text>dshajkl</text></revision></page> > <page><id>774932</id><title>foo</title><revision><id>233192</id><timestamp>2002-12-20T02:12:21Z</timestamp><text>blaaaaa</text></revision></page> > <page><id>732819</id><title>blubb</title><revision><id>233192</id><timestamp>2001-02-21T02:12:21Z</timestamp><text>tztztz</text></revision></page> > <page><id>372819</id><title>bla</title><revision><id>233192</id><timestamp>2001-01-21T02:12:21Z</timestamp><text>blaaaaa</text></revision><revision><id>e7777</id><timestamp>2001-01-21T02:12:21Z</timestamp><text>blubb</text></revision></page> > <page><id>732819</id><title>blubb</title><revision><id>233192</id><timestamp>2000-01-20T02:12:21Z</timestamp><text>blaaaaa</text></revision></page> > > The reverse order would be great. > > BTW: I would like to add a root-Element, since XML requires a root node. > I assume it's not possible to determine if the first and last reduce-Job > is running!? > > regards, > Johannes >
