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Posted to dev@avro.apache.org by "Andy Coates (JIRA)" <ji...@apache.org> on 2018/08/03 13:33:00 UTC

[jira] [Commented] (AVRO-2164) Make Decimal a first class type.

    [ https://issues.apache.org/jira/browse/AVRO-2164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16568212#comment-16568212 ] 

Andy Coates commented on AVRO-2164:
-----------------------------------

Hi [~nkollar],

 

This is what the docs currently say, but this isn't really workable. If the implementation was changes to enforce this, then it would be impossible to change the scale or precision of a decimal. Doing some would result in incompatible schemas. IMHO no evolution is not a good thing.

Hence, I think we should change the docs and the implementation.

> Make Decimal a first class type.
> --------------------------------
>
>                 Key: AVRO-2164
>                 URL: https://issues.apache.org/jira/browse/AVRO-2164
>             Project: Avro
>          Issue Type: Improvement
>          Components: logical types
>    Affects Versions: 1.8.2
>            Reporter: Andy Coates
>            Priority: Major
>
> I'd be interested to hear the communities thoughts on making decimal a first class type. 
> The current logical type encodes a decimal into a _bytes_ or _fixed_. This encoding does not include any information about the scale, i.e. this encoding is lossy. 
> There are open issues around the compatibility / evolvability of schemas containing decimal logical types, (e.g. AVRO-2078 & AVRO-1721), that mean reading data that was previously written with a different scale will result in data corruption.
> If these issues were fixed, with suitable compatibility checks put in place, this would then make it impossible to evolve an Avro schema where the scale needs to be changed. This inability to evolve the scale is very restrictive, and can result in high overhead for organizations that _need_ to change the scale, i.e. they may potentially need to copy their entire data set, deserializing with the old scale and re-serializing with the new.
> If _decimal_ were promoted to a first class type, this would allow the scale to be captured in the serialized form, allow for schema evolution support.



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