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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AVRO-1704) Standardized format for encoding messages with Avro
Date Tue, 28 Jun 2016 19:58:57 GMT

    [ https://issues.apache.org/jira/browse/AVRO-1704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15353614#comment-15353614
] 

Doug Cutting commented on AVRO-1704:
------------------------------------

That decoder interface seems particularly wide.  Might these be better as base classes rather
than interfaces?  What power does the interface add?

The initial implementations also have hidden performance pitfalls; some operations allocate
streams & arrays for every call.  We might either go with a lean-and-mean API, or make
sure that all of the supported invocations are efficient.  I'd prefer inefficiencies be manifest,
forcing clients to allocate streams per call rather than folks assuming they're using a ByteBuffer-optimized
API.

To optimize these in a thread-safe manner I think we'd add a ThreadLocal<ByteArrayInput/OutputStream>
field, right?

Do we really need the raw format support?  This is supported by the existing API.  The primary
goal here is to add support for a new, non-raw "message" format.

Without the interface & the raw format, this could become just two utility classes, MessageEncoder
and MessageDecoder.  Is that too reductive?

> 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
>            Assignee: Niels Basjes
>         Attachments: AVRO-1704-2016-05-03-Unfinished.patch, AVRO-1704-20160410.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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