[C++][Parquet] Integer dictionary bitwidth preservation breaks multi-file read behaviour in pyarrow 20 #46629
Description
Describe the bug, including details regarding any error messages, version, and platform.
This issue was first posed as a question in #30302. I repeat the text here for convenience.
Overview
I have a directory of parquet files. For a specific categorical column, some parquet files use int8 and some use int16. In pyarrow 19.0.1, reading the directory as a dataset succeeds. But with pyarrow 20, it fails with the below error when loading data from the dataset directory
Reader code (python)
Either
import pandas as pd
df = pd.read_parquet(
path,
engine="pyarrow",
)or
import pyarrow.dataset as dataset
dataset = dataset.dataset(path, format="parquet")
table = dataset.to_table()
df = table.to_pandas()
Traceback
File "/app/venv/lib/python3.12/site-packages/pyarrow/parquet/core.py", line 1475, in read
table = self._dataset.to_table(
^^^^^^^^^^^^^^^^^^^^^^^
File "pyarrow/_dataset.pyx", line 589, in pyarrow._dataset.Dataset.to_table
File "pyarrow/_dataset.pyx", line 3941, in pyarrow._dataset.Scanner.to_table
File "pyarrow/error.pxi", line 155, in pyarrow.lib.pyarrow_internal_check_status
File "pyarrow/error.pxi", line 92, in pyarrow.lib.check_status
pyarrow.lib.ArrowInvalid: Integer value 731 not in range: -128 to 127Parquet Metadata
This shows the dictionary info of the parquet files in the directory:
>>> import pyarrow.dataset as dataset
>>> ds = dataset(path)
>>> for path in ds.files:
... sch = pq.read_schema(path)
... print(path, sch.field('ExpStartDate').type)
...
dataframes.parq/00eac90ef2f504223a74498405e060a48.parquet dictionary<values=string, indices=int8, ordered=0>
dataframes.parq/0641c30f725cd448bafc335d36cd01f6b.parquet dictionary<values=string, indices=int16, ordered=0>
dataframes.parq/0cb2799478dd54c738efe76fdc1875326.parquet dictionary<values=string, indices=int8, ordered=0>
dataframes.parq/0cff477be69be4ee093d98728d4f84452.parquet dictionary<values=string, indices=int16, ordered=0>
dataframes.parq/0d103de6323904e93aecf24589c12a370.parquet dictionary<values=string, indices=int8, ordered=0>Is my issue related to the change in #30302 ? Is there a way to restore the previous behaviour of upcasting to int32 on read? Or what is the preferred workaround? It is going to be quite tedious to have to force all my writes to use int32, and especially for migrating huge volumes of historical data. For now we remain on pyarrow 19.0.1, but at some point we would like to upgrade.
Component(s)
C++, Parquet, Python