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https://issues.apache.org/jira/browse/AVRO-1402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13943463#comment-13943463
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Ryan Blue commented on AVRO-1402:
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bq. i) whether this is a good approach for adding new (optional) types to Avro
+1 for the sub-types. I think that's a good way to provide backward-compat. My
only reservation is that calling it a "subType" makes me think there is an "is
a" relationship. What about calling it a "logicalType"?
For existing applications, isn't compatibility covered by the read schema? If
an application isn't setting the read schema and a file is written with a
changed schema, then there isn't a strong compatibility guarantee. But setting
a read schema that doesn't include the subtype annotation should guarantee
compatibility.
bq. What are the use cases we enable by setting precision and scale on a
per-record basis rather than setting it in the schema?
The one I came up with is storing decimals with the right number of significant
figures. The example on
[wikipedia|https://en.wikipedia.org/wiki/Significance_arithmetic] for
multiplication is 8.02 * 8.02 = 64.3 (p=3, s=1). BigDecimal will carry out the
easiest multiplication and produce 64.3204 (p=6, s=4) and the fixed-scale
representation will produce 62.32 (p=4, s=2) with one extra, non-significant
figure. But I'm not sure that this is actually something people would (or do)
use.
bq. smaller scale and precision may be stored in such columns
If it is the case that smaller scales can be stored, then I think we are forced
into storing the scale as data.
> Support for DECIMAL primitive type
> ----------------------------------
>
> Key: AVRO-1402
> URL: https://issues.apache.org/jira/browse/AVRO-1402
> Project: Avro
> Issue Type: New Feature
> Affects Versions: 1.7.5
> Reporter: Mariano Dominguez
> Priority: Minor
> Labels: Hive
> Attachments: AVRO-1402.patch
>
>
> Currently, Avro does not seem to support a DECIMAL type or equivalent.
> http://avro.apache.org/docs/1.7.5/spec.html#schema_primitive
> Adding DECIMAL support would be particularly interesting when converting
> types from Avro to Hive, since DECIMAL is already a supported data type in
> Hive (0.11.0).
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