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Is big Decimal in Parquet big endian?

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Documentation
Clarity
Mostly clear
Activity status
Stale

Research direction

Start with the Parquet data-pages encodings documentation linked in the issue and verify the byte order and encoding rules for BYTE_ARRAY and FIXED_LEN_BYTE_ARRAY decimal values. Done means documenting whether big decimals use big-endian or little-endian bytes and when any encoding or byte swapping occurs.

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Description

Describe the usage question you have. Please include as many useful details as possible.

It's not clear from description https://parquet.apache.org/docs/file-format/data-pages/encodings/ how are big Decimals (precision >= 18) placed. As I could understand they can be encoded as BYTE_ARRAY or FIXED_LEN_BYTE_ARRAY. But there're two ways to place "the bytes contained in the array" from memory: big endian and little endian. I.e. they are in LE in int128 in memory. Could I place the bytes into FIXED_LEN_BYTE_ARRAY as is?

It's also not clean if there's some encoding over these decimal's bytes, should the data be swapped to correct endianness before of after the encoding?

Component(s)

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Dominant language
Java
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