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Overview
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The Hama is based on the Bulk Synchronous Parallel Model (BSP), in which a computation involves a number of supersteps, each having many distributed computational peers that synchronize at the end of the superstep. Basically, a BSP program consists of a sequence of supersteps. Each superstep consistsof the following three phases:
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Hama provides a user-defined function “bsp()” that can be used to write your own BSP program. The bsp() function handles the whole parallel part of the program. In the 0.2 version, it It only takes one argument "BSPPeer", which is a communication protocol interface. Later, more arguments such as input or reporter could also be included.contains an communication, counters, and IO interfaces.
Inputs and Outputs
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Communication Model
Within the bsp() function, you can use the powerful communication functions for many purposes using BSPPeer. We tried to follow the standard library of BSP world as much as possible. The following table describes all the functions you can use:
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The BSP job will be finished only when all processes have no more local and outgoing queues entries and all processes done or is killed by the user.
Counters
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Setup and
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Cleanup
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Combiners
Combiners are used for performing message aggregation to reduce communication overhead in cases when messages can be summarized arithmetically e.g., min, max, sum, and average at the sender side. Suppose that you want to send the integer messages to a specific processor from 0 to 1000 and sum all received the integer messages from all processors.
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public static class SumCombiner extends Combiner {
@Override
public BSPMessageBundle combine(Iterable<BSPMessage> messages) {
BSPMessageBundle bundle = new BSPMessageBundle();
int sum = 0;
Iterator<BSPMessage> it = messages.iterator();
while (it.hasNext()) {
sum += ((IntegerMessage) it.next()).getData();
}
bundle.addMessage(new IntegerMessage("Sum", sum));
return bundle;
}
}
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— General Information —
In Apache Hama, you can implement your own BSP method by extending from org.apache.hama.bsp.BSP class. Apache Hama provides in this class a user-defined function bsp() that can be used to write your own BSP program.
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