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https://issues.apache.org/jira/browse/AVRO-2164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16411698#comment-16411698
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Ryan Blue commented on AVRO-2164:
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The current decimal type is a fixed scale, so you use the same scale for an
entire file. This matches the behavior of decimal columns in SQL. I'm not sure
what you mean by "provided by Avro out of the box". When you read decimals, the
BigDecimal instances have the column's scale. Avro should also verify that all
of the decimals passed in have the correct scale and reject them.
> 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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