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https://issues.apache.org/jira/browse/AVRO-1704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15190866#comment-15190866
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Niels Basjes commented on AVRO-1704:
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Thanks for pointing this out.
My updated proposal for this:
{code}"Avro"<version><fingerprint><record>{code}
Where
# "version" = 1 byte indicating the version (or "schema") of the rest of the
bytes.
if version == 0x00
# "Fingerprint" = the CRC-64-AVRO of the Canonical form of the Schema.
# "Record" = the record serialized to byte using the existing serialization
system.
I personally do not like these 'chopped' prefixes if there is no "really good
reason to chop them" (like the length).
Because the projects name is so short: In this proposal I'm sticking to using
the full name of the project as the prefix: "Avro" (i.e. these 4 bytes 0x41,
0x76, 0x72, 0x6F)
> Standardized format for encoding messages with Avro
> ---------------------------------------------------
>
> Key: AVRO-1704
> URL: https://issues.apache.org/jira/browse/AVRO-1704
> Project: Avro
> Issue Type: Improvement
> Reporter: Daniel Schierbeck
>
> 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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