Core, Parquet: Fix null counting for parquet that doesn't have null_c… - #17557
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xndai wants to merge 6 commits into
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Core, Parquet: Fix null counting for parquet that doesn't have null_c…#17557xndai wants to merge 6 commits into
xndai wants to merge 6 commits into
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…ount stats Parquet's Statistics#getNumNulls returns -1 when null_count is missing from the stats. But our current metrics logic doesn't handle this -1 value specifically, instead it just adds to the existing count. For a single row group the -1 total was dropped because Metrics only keeps non-negative counts. But say we have row group 0 that has one null value and row group 1 doesn't have null_count stats and return -1, we end up counting total null count as 0, which is wrong. A query engine that relys on total null count being 0, can skip the file completely when evaluating predicate like `WHERE c IS NULL` causing wrong results. Fix by checking the -1 when sum the nulls. Add corresponding tests.
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Issue #17558 |
anoopj
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Aug 9, 2026
anoopj
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The core code change looks good to me. This is an important correctness fix - thanks for catching this!
I have a couple of comments on tests.
Address review feedback: the manifest round-trip test does not need the filesystem. Use InMemoryOutputFile and InMemoryFileIO instead of a temp directory, following TestVariantMetrics.
Address review feedback: the variant metrics paths handle a missing null_count too, but had no test for it. Add cases that build a two row group footer where one row group omits the variant column's null_count, covering both the footer null count path and the all-null-variant path that uses the value count instead.
The merge of main dropped the @test annotation from testShreddedStringBoundsAcrossRowGroups (added upstream in apache#17397), so JUnit silently skipped it. Restore the annotation so the test runs again.
singhpk234
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Aug 11, 2026
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Thanks for fix @xndai, I added this to 1.12 milestone too keep track of it
| // without accounting for the -1 sentinel, this sums to an incorrect null count of 0 | ||
| Metrics metrics = metrics(block(statsWithoutNullCount(1, 10), 10), block(stats(20, 30, 1), 10)); | ||
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| assertThat(metrics.nullValueCounts()).doesNotContainKey(1); |
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should we instead assert what the val returned is ? -1 right ?
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The -1 is returned from Statistics.getNumNulls() as an internal sentinel to represent unknown state. But when the null count is stored into Metrics, -1 is dropped so here we assert the null value count is unavailable in the map.
Address review feedback: follow the convention of omitting the redundant "test" prefix on test method names.
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…ount stats
Parquet's Statistics#getNumNulls returns -1 when null_count is missing from the stats. But our current metrics logic doesn't handle this -1 value specifically, instead it just adds to the existing count.
For a single row group the -1 total was dropped because Metrics only keeps non-negative counts. But say we have row group 0 that has one null value and row group 1 doesn't have null_count stats and return -1, we end up counting total null count as 0, which is wrong. A query engine that relays on total null count being 0, can skip the file completely when evaluating predicate like
WHERE c IS NULLcausing wrong results.Fix by checking the -1 when sum the nulls. Add corresponding tests.