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Fix invalid use of std::exclusive_scan in Parquet writer #13434

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merged 6 commits into from
May 25, 2023
+4 −12
Merged

Fix invalid use of std::exclusive_scan in Parquet writer #13434

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a5164da
fix invalid use of std::exclusive_scan
etseidl May 24, 2023
d8b4092
Update cpp/src/io/parquet/writer_impl.cu
etseidl May 24, 2023
b4a3161
review suggestion
etseidl May 24, 2023
f6277f0
clean up total_frags calculation
etseidl May 24, 2023
0a3658a
Merge branch 'branch-23.06' into fix_off_by_one
etseidl May 24, 2023
a6673a1
Merge branch 'rapidsai:branch-23.06' into fix_off_by_one
etseidl May 25, 2023
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4 changes: 2 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 @@ -1710,10 +1710,10 @@ auto convert_table_to_parquet_data(table_input_metadata& table_meta,
size_type const total_frags = [&]() {
if (frags_per_column.size() > 0) {
std::exclusive_scan(frags_per_column.data(),
frags_per_column.data() + num_columns + 1,
frags_per_column.data() + num_columns,
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Let's use frags_per_column.begin(), frags_per_column.end().

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Also please avoid back_inserter if possible. So this should be better:

std::vector<size_type> frag_offsets(num_columns, 0);
...
std::exclusive_scan(frags_per_column.begin(), frags_per_column.end(), frag_offsets.begin(), 0);

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much cleaner. thanks!

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AFAIK, the canonical way is to reserve the final size and use back_inserter, so we never reallocate and never default-initialize elements. It is unfortunatelly also the most verbose option 🤷‍♂️
Not a request to apply this here, just an FYI (or maybe a FMI, if @ttnghia knows of a back_inserter drawback).

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I like that. I wouldn't mind changing to that just so it's in my muscle memory :)

std::back_inserter(frag_offsets),
0);
return frag_offsets[num_columns];
return frag_offsets[num_columns - 1] + frags_per_column[num_columns - 1];
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} else {
return 0;
}
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