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From Apache Wiki <wikidi...@apache.org>
Subject [Hama Wiki] Update of "Aggregators" by AnastasisAndronidis
Date Sun, 26 Jan 2014 17:18:08 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hama Wiki" for change notification.

The "Aggregators" page has been changed by AnastasisAndronidis:
https://wiki.apache.org/hama/Aggregators?action=diff&rev1=3&rev2=4

  == Aggregators ==
  
- === Description ===
+ === Introduction ===
  Quoting from Pregel paper: ''aggregators are a mechanism for global communication, monitoring,
and data. Each vertex can provide a value to an aggregator in superstep S, the system combines
those values using a reduction operator, and the resulting value is made available to all
vertices in superstep S + 1.''
  
  You can think aggregators as a tree, that the leafs (which are the graph vertices) are sending
messages to the root (the master aggregator), and then the root is combining all these messages
to a value. In the end, this combined values is distributed back to the leafs. Aggregators
are useful for statistics (think of an histogram of vertex degrees) or for global controlling.
  
- === Introduction ===
+ === Registering aggregators ===
+ To start using aggregators, you must register them in your GraphJob.
  
+ e.g.
+ {{{
+ HamaConfiguration conf = new HamaConfiguration(new Configuration());
+ GraphJob graphJob = new GraphJob(conf, MyClass.class);
+ 
+ // To add an average aggregator
+ graphJob.setAggregatorClass(AverageAggregator.class);
+ 
+ // To add a sum aggregator
+ graphJob.setAggregatorClass(SumAggregator.class);
+ }}}
+ 
+ There are lots of different aggregators and you can also make your own. Look for already
implemented aggregators in org.apache.hama.graph package.
+ 

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