[BUG] Chunked parquet reader incorrect results for positive values of n_rows

[brandon-b-miller]

With 24.12, I have:

import pylibcudf as plc
import pyarrow as pa
import pyarrow.parquet as pq


data = {
            "a": [1, 2, 3, None, 4, 5],
            "b": ["ẅ", "x", "y", "z", "123", "abcd"],
            "c": [None, None, 4, 5, -1, 0],
        }


path = "./test.parquet"
pq.write_table(pa.Table.from_pydict(data), path)

reader = plc.io.parquet.ChunkedParquetReader(
        plc.io.SourceInfo([path]),
        columns=['a', 'b', 'c'],
        nrows=2,
        skip_rows=0,
        chunk_read_limit=0,
        pass_read_limit=17179869184 # 16 GiB
)

# Read data by chunk
chk = reader.read_chunk()
tbl = chk.tbl
names = chk.column_names()
concatenated_columns = tbl.columns()
while reader.has_next():
    tbl = reader.read_chunk().tbl

    for i in range(tbl.num_columns()):
        concatenated_columns[i] = plc.concatenate.concatenate(
            [concatenated_columns[i], tbl._columns[i]]
        )
        # Drop residual columns to save memory
        tbl._columns[i] = None

gpu_result = plc.interop.to_arrow(tbl)
cpu_result = pq.read_table(path)[:2]

print(cpu_result.column(1).to_pylist())
print(gpu_result.column(1).to_pylist())

This results in

['ẅ', 'x']
['ẅ', 'x\x00\x00\x00\x00\x00\x00\x00\x00\x00']

[vyasr]

Based on this comment could this be related to #16186 @mhaseeb123?

[mhaseeb123]

Based on this comment could this be related to #16186 @mhaseeb123?

Nah, as discussed offline, this one is related to the decoder while #16186 is related to chunking.