ORC Format

ORC (Optimized Row Columnar) is a columnar storage file format designed for Hadoop workloads. It provides efficient data compression and encoding schemes, as well as support for complex types like nested structures and dates. ORC files are optimized for both read and write operations, making them ideal for largescale data processing tasks.

Key Features of ORC Format

ORC File Structure

An ORC file consists of several components:

1、File Header: Contains metadata about the file, such as the number of rows, columns, and their types.

2、Row Index: Provides a mapping from row numbers to the start position of each row in the stripes.

3、Stripes: Contain the actual data in a columnar format. Each stripe contains one or more rows of data.

4、Footer: Contains additional metadata, such as statistics about the data.

Using ORC with MapReduce

ORC files can be processed using MapReduce jobs just like any other file format. TheOrcInputFormat andOrcOutputFormat classes provide input and output support for ORC files.

Reading ORC Files with MapReduce

To read an ORC file in a MapReduce job, you need to set up theOrcInputFormat class in your job configuration:

Job job = Job.getInstance(new Configuration());
FileInputFormat.addInputPath(job, new Path("path/to/orc/file"));
OrcInputFormat.setInputPathFilter(job, OrcInputFormat.class);

Writing ORC Files with MapReduce

To write data to an ORC file using MapReduce, you need to use theOrcOutputFormat class:

Job job = Job.getInstance(new Configuration());
FileOutputFormat.setOutputPath(job, new Path("path/to/output/directory"));
OrcOutputFormat.setOutputPath(job, new Path("path/to/output/orc/file"));

By leveraging the ORC format and its integration with MapReduce, you can efficiently process large datasets while taking advantage of the benefits provided by the columnar storage format.