Can we write the output of MapReduce in different formats?
MapReduce default Hadoop reducer Output Format is TextOutputFormat, which writes (key, value) pairs on individual lines of text files and its keys and values can be of any type since TextOutputFormat turns them to string by calling toString() on them.
How MapReduce jobs can be optimized?
6 Best MapReduce Job Optimization Techniques
- Proper configuration of your cluster.
- LZO compression usage.
- Proper tuning of the number of MapReduce tasks.
- Combiner between Mapper and Reducer.
- Usage of most appropriate and compact writable type for data.
- Reusage of Writables.
In what form reducer output is presented?
As we know, Reducer takes Mappers intermediate output as input. Then it runs a reducer function on them to generate output that is again zero or more key-value pairs. So, RecordWriter in MapReduce job execution writes these output key-value pairs from the Reducer phase to output files.
Why do we reduce map?
MapReduce is suitable for iterative computation involving large quantities of data requiring parallel processing. It represents a data flow rather than a procedure. A graph may be processed in parallel using MapReduce. Graph algorithms are executed using the same pattern in the map, shuffle, and reduce phases.
How does map and reduce work?
The MapReduce algorithm contains two important tasks, namely Map and Reduce. Map takes a set of data and converts it into another set of data, where individual elements are broken down into tuples (key/value pairs). As the sequence of the name MapReduce implies, the reduce task is always performed after the map job.
What is RecordReader in a map reduce?
What is RecordReader in MapReduce? A RecordReader converts the byte-oriented view of the input to a record-oriented view for the Mapper and Reducer tasks for processing.
How does map reduce improve performance?
Some more tips :
- Configure the cluster properly with right diagnostic tools.
- Use compression when you are writing intermediate data to disk.
- Tune number of Map & Reduce tasks as per above tips.
- Incorporate Combiner wherever it is appropriate.