Glossary of terms:

• 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 ontop 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. These live in a particular row group and is 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 is interleaved in a column chunk.

Hierarchically, a file consists of one or more rows 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