How are Parquet files structured? (Row Groups, Column Chunks, Pages)?

Parquet organises data in a three-level hierarchy:

• Row Group — a horizontal slice of the dataset, typically 128 MB–1 GB of data. Each row group contains one column chunk per column.
• Column Chunk — all values for a single column within a row group. This is the unit of compression and encoding.
• Page — the smallest addressable unit inside a column chunk (default 1 MB). Pages can be data pages, dictionary pages, or index pages.

At the end of the file, a footer stores the schema and per-column statistics (min, max, null count, distinct count). Readers fetch the footer first to plan which row groups and pages to skip.

Parquet File\n├── Row Group 1 (128 MB)\n│   ├── Column Chunk: id\n│   ├── Column Chunk: name\n│   └── Column Chunk: amount\n├── Row Group 2\n│   └── ...\n└── Footer (schema + statistics)

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