Add configuration option to StatisticsConverter to control interpretation of missing null counts in Parquet statistics - #6485
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alamb
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Oct 1, 2024
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## Which issue does this PR close? Closes apache#25239. Follows up on apache#21907 and [Arrow apache#6485](apache/arrow-rs#6485). ## Rationale for this change An absent Parquet `null_count` is unknown. Treating it as zero can discard NULL rows during `NULLS FIRST` TopK and `IS NULL` pruning, and let metadata-only `COUNT(column)` return an incorrect result. ## What changes are included in this PR? Preserve missing null counts in the shared row-group statistics adapter and file statistics. Remove the per-caller compatibility flag so static pruning, runtime pruning, and fully matched proofs use the same interpretation. Add an upgrade guide covering affected writers, plan changes, and migration. ## What is the testing strategy for this PR? Regressions cover missing and explicit-zero counts, static pruning, file-statistics precision, `COUNT`, and TopK with ASC/DESC, NULLS FIRST/LAST, and dynamic pruning enabled/disabled. The affected cases fail without the fix. Extended workspace tests, strict all-target/all-feature Clippy, and the full lint suite pass. ## Are there any user-facing changes? Correct results for Parquet files with missing null counts. Affected files can lose `IS NULL` pruning, metadata-only `COUNT(column)`, and `NULLS FIRST` TopK pruning. Sort pushdown can also retain a full `SortExec` for `ORDER BY` on nullable columns, even when files are sorted and non-overlapping. This includes older files written with parquet-rs before 53.1.0, used by DataFusion releases before 42.1.0. The DataFusion 56 upgrade guide explains how to identify and rewrite affected files. Explicit counts retain their existing behavior. No public API changes. --------- Signed-off-by: peterxcli <peterxcli@gmail.com>
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Which issue does this PR close?
Part of #6256.
Rationale for this change
In #6257 @alamb changes the behavior of the parquet writer to always write
Some(0)when the null count is known to be zero. Part of #6257 allows users ofStatisticsConverterto choose whether or not to treat missing null counts as 0.What changes are included in this PR?
This PR consists of @alamb's changes to
StatisticsConverterwithout the changes to writer behavior. By default no behavior is changed, but users can prepare for later changes to how theStatistics::null_countfield is written.See the conversation here for the rationale.
Are there any user-facing changes?
No.