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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2021/01/24 09:49:02 UTC

[GitHub] [arrow] jorgecarleitao commented on pull request #9232: ARROW-10818: [Rust] Implement DecimalType

jorgecarleitao commented on pull request #9232:
URL: https://github.com/apache/arrow/pull/9232#issuecomment-766319983


   Hi @ovr , I went through what is here so far.
   
   First of all, great stuff that you are taking this on.
   
   Broadly speaking, this PR currently contains the following "steps":
   
   1. make changes to the arrow crate to enable Decimal type without adding any new functionality (e.g. rename `datatypes.rs`) 
   2. add the native type to the arrow crate
   3. add the Array type to the arrow crate
   4. add support to parquet
   5. add support to DataFusion
   
   I suggest that 4-5 are done on a separate PR. 1-3 can be done on this PR, but I suggest that we split them on separate commits.
   
   Concerning step 2, the two main checks in the list are:
   
   1. the type's logical representation exists in the arrows' spec
   2. the type's physical representation matches arrows' spec
   
   Looking at [the spec](https://github.com/apache/arrow/blob/master/format/Schema.fbs#L186), a decimal type only supports 128 and 256 bits. So, I am do not understand why we are trying to add support for `Int32,Int64,Int128,LargeDecimal` here. Since Rust only supports `i128`, I would say that we should only go for `i128` (the same reason we do not support `f16`).
   
   A related aspect is that `bigint`'s official documentation states
   
   > DEPRECATED
   > This crate is deprecated and will not be developed further. Users are invited to prefer the uint crate instead.
   
   thus, I am not sure we want to take that as a dependency.
   
   Could you clarify some of these points?


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