Block (HDFS block): This means a block in HDFS and the meaning is unchanged for describing this file format. The file format is designed to work well on top of HDFS.
File: A HDFS file that must include the metadata for the file. It does not need to actually contain the data.
Row group: A logical horizontal partitioning of the data into rows. There is no physical structure that is guaranteed for a row group. A row group consists of a column chunk for each column in the dataset.
Column chunk: A chunk of the data for a particular column. They live in a particular row group and are guaranteed to be contiguous in the file.
Page: Column chunks are divided up into pages. A page is conceptually an indivisible unit (in terms of compression and encoding). There can be multiple page types which are interleaved in a column chunk.
Hierarchically, a file consists of one or more row groups. A row group contains exactly one column chunk per column. Column chunks contain one or more pages.
Unit of parallelization
- MapReduce - File/Row Group
- IO - Column chunk
- Encoding/Compression - Page