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Write parquet column chunk file_offset #15882

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Write parquet column chunk file_offset #15882

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7 changes: 5 additions & 2 deletions cpp/src/io/parquet/writer_impl.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -2486,8 +2486,11 @@ void writer::impl::write_parquet_data_to_sink(
_out_sink[p]->host_write(bounce_buffer.data(), ck.compressed_size);
}

auto const chunk_offset = _current_chunk_offset[p];
auto& column_chunk_meta = row_group.columns[i].meta_data;
auto const chunk_offset = _current_chunk_offset[p];
auto& column_chunk = row_group.columns[i];
column_chunk.file_offset = chunk_offset;

@etseidl etseidl May 29, 2024

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Danger Will Robinson! There appears to be confusion in the community about what file_offset is. According to the parquet thrift this points to the chunk metadata, not the start of the chunk. This allows for the metadata to be separated from the thrift in the footer, both to allow for faster parsing, and to support data living in a file separate from where the footer is located. (See apache/parquet-format#242 (comment) for some discussion of the latter use case). It seems as though parquet-mr incorrectly populates this with the offset of the first page, while arrow does what the spec mandates and uses it to point to a duplicate copy of the ColumnMetaData that is located at the end of a column chunk (as per the figure in the spec). Since libcudf does not write this copy, it's best to leave this field as '0'.

@pmattione-nvidia pmattione-nvidia May 29, 2024

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Ah I see. OK, I'll close this PR.


auto& column_chunk_meta = column_chunk.meta_data;
column_chunk_meta.data_page_offset =
chunk_offset + ((ck.use_dictionary) ? ck.dictionary_size : 0);
column_chunk_meta.dictionary_page_offset = (ck.use_dictionary) ? chunk_offset : 0;
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