Of couurse !!! It's logical. Thank you John. 2011/5/27 John Armstrong <[email protected]>
> On Fri, 27 May 2011 13:52:04 +0200, Laurent Hatier > <[email protected]> wrote: > > I'm a newbie with Hadoop/MapReduce. I've a problem with hadoop. I set > some > > variables in the run function but when Map running, he can't get the > value > > of theses variables... > > If anyone knows the solution :) > > By the "run function" do you mean the main method that launches the > map/reduce job? It's no surprise that the mappers (and reducers) won't > know those variables, because they run as completely separate tasks. > > If you're computing something in the setup method for use in the mappers > or reducers you'll have to pass that information along somehow. If it's a > String (or something that can easily be made into a String, like an int) > you can set it as a property in the job's Configuration. For more > complicated data you'll have to serialize it to a file, place the file into > the distributed cache, and then deserialize the data within the mapper or > reducer's setup method. > > Of course, if the computation is less complicated/time consuming than the > deserialization process, you may as well just recompute the data in each > mapper or reducer. > -- Laurent HATIER Étudiant en 2e année du Cycle Ingénieur à l'EISTI
