> Standardized format for encoding messages with Avro
> Key: AVRO-1704
> URL: https://issues.apache.org/jira/browse/AVRO-1704 > Project: Avro
> Issue Type: Improvement
> Components: java, spec
> Reporter: Daniel Schierbeck
> Assignee: Niels Basjes
> Fix For: 1.9.0, 1.8.2
> Attachments: AVRO-1704-20160410.patch, AVRO-1704-2016-05-03-Unfinished.patch, AVRO-1704.3.patch, AVRO-1704.4.patch
> I'm currently using the Datafile format for encoding messages that are written to Kafka and Cassandra. This seems rather wasteful:
> 1. I only encode a single record at a time, so there's no need for sync markers and other metadata related to multi-record files.
> 2. The entire schema is inlined every time.
> However, the Datafile format is the only one that has been standardized, meaning that I can read and write data with minimal effort across the various languages in use in my organization. If there was a standardized format for encoding single values that was optimized for out-of-band schema transfer, I would much rather use that.
> I think the necessary pieces of the format would be:
> 1. A format version number.
> 2. A schema fingerprint type identifier, i.e. Rabin, MD5, SHA256, etc.
> 3. The actual schema fingerprint (according to the type.)
> 4. Optional metadata map.
> 5. The encoded datum.
> The language libraries would implement a MessageWriter that would encode datums in this format, as well as a MessageReader that, given a SchemaStore, would be able to decode datums. The reader would decode the fingerprint and ask its SchemaStore to return the corresponding writer's schema.
> The idea is that SchemaStore would be an abstract interface that allowed library users to inject custom backends. A simple, file system based one could be provided out of the box.
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