External indexes, metadata stores, catalogs, and caches can significantly enhance query performance on Apache Parquet by allowing efficient data retrieval without the need for extensive reparsing. The blog discusses how to implement these components using Apache DataFusion to optimize custom data platforms for specific use cases. It also highlights the advantages of Parquet's hierarchical data organization and its compatibility with various indexing strategies.

User-defined indexes can be embedded within Apache Parquet files, enhancing query performance without compatibility issues. By utilizing existing footer metadata and offset addressing, developers can create custom indexes, such as distinct value indexes, to improve data pruning efficiency, particularly for columns with limited distinct values. The article provides a practical example of implementing such an index using Apache DataFusion.