Hadoop: The Definitive Guide, 4th Edition

Chapter 12. Avro

Apache Avro^[79] is a language-neutral data serialization system. The project was created by Doug Cutting (the creator of Hadoop) to address the major downside of Hadoop Writables: lack of language portability. Having a data format that can be processed by many languages (currently C, C++, C#, Java, JavaScript, Perl, PHP, Python, and Ruby) makes it easier to share datasets with a wider audience than one tied to a single language. It is also more future-proof, allowing data to potentially outlive the language used to read and write it.

But why a new data serialization system? Avro has a set of features that, taken together, differentiate it from other systems such as Apache Thrift or Google’s Protocol Buffers.^[80] Like in these systems and others, Avro data is described using a language-independent schema. However, unlike in some other systems, code generation is optional in Avro, which means you can read and write data that conforms to a given schema even if your code has not seen that particular schema before. To achieve this, Avro assumes that the schema is always present—at both read and write time—which makes for a very compact encoding, since encoded values do not need to be tagged with a field identifier.

Avro schemas are usually written in JSON, and data is usually encoded using a binary format, but there are other options, too. There is a higher-level language called Avro IDL for writing schemas in a C-like language that is more familiar to developers. There ...