[PARQUET-1869] [C++] Large decimal values don't roundtrip correctly

• Type: Test
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: parquet-cpp
• Assignee: Unassigned
• Reporter: Joris Van den Bossche
• Created: 02/Jun/20 07:51
• Updated: 02/Jun/20 12:40

Description

Reproducer with python:

import decimal
import pyarrow as pa
import pyarrow.parquet as pq

arr = pa.array([decimal.Decimal('9223372036854775808'), decimal.Decimal('1.111')])
print(arr)

pq.write_table(pa.table({'a': arr}), "test_decimal.parquet") 
result = pq.read_table("test_decimal.parquet")
print(result.column('a'))

gives

# before writing
<pyarrow.lib.Decimal128Array object at 0x7fd07d79a468>
[
  9223372036854775808.000,
  1.111
]
# after reading
<pyarrow.lib.ChunkedArray object at 0x7fd0711e9f98>
[
  [
    -221360928884514619.392,
    1.111
  ]
]

I tried reading the file with a different parquet implementation (fastparquet python package), and that gives the same values on read, so the issue might possibly rather be on the write side.