Скачать или смотреть 9 WORD Count Program Using Map Reduce (JAVA and Python)

A Word Count Program using Python and Java Running as Map Reduce Job (For Python Map Reduce Streaming)


1. Map Phase:

The input data is divided into chunks, and each chunk is processed by a separate map task.
You write a Map function that takes an input key-value pair and emits intermediate key-value pairs as output.
The Map function processes data in parallel across multiple nodes in the cluster.
2. Shuffle and Sort Phase:

After the Map phase, the intermediate key-value pairs from all the map tasks are shuffled and sorted based on their keys.
This grouping of key-value pairs with the same key ensures that all values for a given key are processed together in the Reduce phase.

3. Reduce Phase:

You write a Reduce function that takes the sorted key-value pairs as input and performs some aggregation or computation.
Each Reduce task processes a unique key and its associated values.
Here are some key concepts and considerations for MapReduce programming:


Partitioning: The MapReduce framework automatically partitions the keys for the Reduce phase, distributing them across multiple reducers.
Combiner: A Combiner function can be used in the Map phase to perform local aggregation before sending data to the Reducers, reducing network traffic and speeding up the process.

Counters: You can use counters to keep track of specific events or metrics during MapReduce job execution, which can be helpful for debugging and monitoring.
Input and Output Formats: MapReduce jobs can handle various input and output formats, such as text, sequence files, or custom formats.
Job Configuration: You can set various parameters and options when configuring a MapReduce job, like the number of mappers, reducers, and other settings.