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Posted to github@arrow.apache.org by "Rich-T-kid (via GitHub)" <gi...@apache.org> on 2026/08/11 20:18:20 UTC
[PR] [Parquet] Add row group column stats [arrow-rs]
Rich-T-kid opened a new pull request, #10652:
URL: https://github.com/apache/arrow-rs/pull/10652
# Which issue does this PR close?
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- works towards #10650.
- works towards [#24114 & ](https://github.com/apache/datafusion/issues/24114) & https://github.com/apache/datafusion/issues/22891
# Rationale for this change
see #10650
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# What changes are included in this PR?
Added StatisticsConverter::row_group_distinct_counts() to the parquet crate, which reads the distinct_count field from row group statistics and returns a UInt64Array with one entry per row group.
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# Are these changes tested?
yes this PR includes two test that assert that row group stats are being propogated
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# Are there any user-facing changes?
yes, adds new public method for reading row group distinct stats
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Re: [PR] [Parquet] Add row group distinct counts to `StatisticsConverter` [arrow-rs]
Posted by "Rich-T-kid (via GitHub)" <gi...@apache.org>.
Rich-T-kid commented on PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652#issuecomment-5260468895
I'll try and see if I can make it more performant and push up the PR tomorrow 👍
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Re: [PR] [Parquet] Add row group distinct counts to `StatisticsConverter` [arrow-rs]
Posted by "etseidl (via GitHub)" <gi...@apache.org>.
etseidl merged PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652
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Re: [PR] [Parquet] Add row group distinct counts to `StatisticsConverter` [arrow-rs]
Posted by "etseidl (via GitHub)" <gi...@apache.org>.
etseidl commented on PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652#issuecomment-5333349580
I think this has waited long enough, thanks @Rich-T-kid.
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Re: [PR] [Parquet] Add row group distinct counts to `StatisticsConverter` [arrow-rs]
Posted by "etseidl (via GitHub)" <gi...@apache.org>.
etseidl commented on PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652#issuecomment-5260428685
> i just ran a simple implementation gated by a boolean flag and it ranges from 1.4x-8.8x slower depending on the data type.
That's quite the hit, glad it's gated. But I can see a use for write-once-read-many scenarios where you'd likely want the cardinality and are willing to pay for it.
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Re: [PR] [Parquet] Add row group distinct counts to `StatisticsConverter` [arrow-rs]
Posted by "Rich-T-kid (via GitHub)" <gi...@apache.org>.
Rich-T-kid commented on PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652#issuecomment-5260367709
> This seems sensible to me, esp. if there are writers that actually populate this statistic.
>
> How to tackle the write side of this is still a matter of debate. 😅
@etseidl i just ran a simple implementation gated by a boolean flag and it ranges from 1.4x-8.8x slower depending on the data type.
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Re: [PR] [Parquet] Add row group column stats [arrow-rs]
Posted by "Rich-T-kid (via GitHub)" <gi...@apache.org>.
Rich-T-kid commented on PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652#issuecomment-5258475059
🤔 datafusion does do something similar here https://github.com/apache/datafusion/blob/041a71671c7a505a2e3ed58689a20137c8f3d172/datafusion/datasource-parquet/src/metadata.rs#L835, but with this PR we allow arrow-rs user to do it directly as well make a consistent api.
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Re: [PR] [Parquet] Add row group distinct counts to `StatisticsConverter` [arrow-rs]
Posted by "Rich-T-kid (via GitHub)" <gi...@apache.org>.
Rich-T-kid commented on PR #10652:
URL: https://github.com/apache/arrow-rs/pull/10652#issuecomment-5333535710
thank you @etseidl
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