Ryan Blue commented on AVRO-1704:

You mean erring on the side of caution and using a larger hash? I don't think 
collisions with a 64-bit fingerprint are likely enough to cause any trouble. 
And, while you don't calculate the fingerprint every time, you do send it in 
the message.

> 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, 1.8.3
>         Attachments: AVRO-1704-2016-05-03-Unfinished.patch, 
> AVRO-1704-20160410.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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