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Minor: simplify DataSource statistics code #8172

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Minor: simplify DataSource statistics code #8172

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68 changes: 5 additions & 63 deletions datafusion/core/src/datasource/statistics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -83,10 +83,9 @@ pub async fn get_statistics_with_limit(
// counts across all the files in question. If any file does not
// provide any information or provides an inexact value, we demote
// the statistic precision to inexact.
num_rows = add_row_stats(file_stats.num_rows, num_rows);
num_rows = num_rows.add(&file_stats.num_rows);

total_byte_size =
add_row_stats(file_stats.total_byte_size, total_byte_size);
total_byte_size = total_byte_size.add(&file_stats.total_byte_size);

(null_counts, max_values, min_values) = multiunzip(
izip!(
Expand All @@ -108,9 +107,9 @@ pub async fn get_statistics_with_limit(
min_value,
)| {
(
add_row_stats(file_nc, null_count),
set_max_if_greater(file_max, max_value),
set_min_if_lesser(file_min, min_value),
file_nc.add(&null_count),
file_max.max(&max_value),
file_min.min(&min_value),
)
},
),
Expand Down Expand Up @@ -160,17 +159,6 @@ pub(crate) fn create_max_min_accs(
(max_values, min_values)
}

fn add_row_stats(
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This is the same as https://github.com/apache/arrow-datafusion/blob/eef654c3b0c22b1f845b1441320b8bb718ddd605/datafusion/common/src/stats.rs#L119-L126

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I think they don't share the same behavior, but it didn't show up due to lack of testing. The add() function operates in the safest way; if one of the operands is absent, the result will also be absent. On the other hand, the remove() function keeps the non-absent value by changing its exactness (absent + exact(value) => inexact(value)).

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It is interesting that there is very similar code in https://github.com/apache/arrow-datafusion/blob/a892300a5a56c97b5b4ddc9aa4a421aaf412d0fe/datafusion/core/src/datasource/file_format/parquet.rs#L503-L525 that uses add 🤔

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It seems like it is always adding exact values, so there should be no difference on the results whether it is used add() or estimated_add()

file_num_rows: Precision<usize>,
num_rows: Precision<usize>,
) -> Precision<usize> {
match (file_num_rows, &num_rows) {
(Precision::Absent, _) => num_rows.to_inexact(),
(lhs, Precision::Absent) => lhs.to_inexact(),
(lhs, rhs) => lhs.add(rhs),
}
}

pub(crate) fn get_col_stats_vec(
null_counts: Vec<Precision<usize>>,
max_values: Vec<Precision<ScalarValue>>,
Expand Down Expand Up @@ -211,49 +199,3 @@ pub(crate) fn get_col_stats(
})
.collect()
}

/// If the given value is numerically greater than the original maximum value,
/// return the new maximum value with appropriate exactness information.
fn set_max_if_greater(
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This is the same as https://github.com/apache/arrow-datafusion/blob/eef654c3b0c22b1f845b1441320b8bb718ddd605/datafusion/common/src/stats.rs#L75-L87

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There is a similar difference here as well. Max values are conserved by relaxing the exactness when an absent statistic is read from the file.

max_nominee: Precision<ScalarValue>,
max_values: Precision<ScalarValue>,
) -> Precision<ScalarValue> {
match (&max_values, &max_nominee) {
(Precision::Exact(val1), Precision::Exact(val2)) if val1 < val2 => max_nominee,
(Precision::Exact(val1), Precision::Inexact(val2))
| (Precision::Inexact(val1), Precision::Inexact(val2))
| (Precision::Inexact(val1), Precision::Exact(val2))
if val1 < val2 =>
{
max_nominee.to_inexact()
}
(Precision::Exact(_), Precision::Absent) => max_values.to_inexact(),
(Precision::Absent, Precision::Exact(_)) => max_nominee.to_inexact(),
(Precision::Absent, Precision::Inexact(_)) => max_nominee,
(Precision::Absent, Precision::Absent) => Precision::Absent,
_ => max_values,
}
}

/// If the given value is numerically lesser than the original minimum value,
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This is the same as https://github.com/apache/arrow-datafusion/blob/eef654c3b0c22b1f845b1441320b8bb718ddd605/datafusion/common/src/stats.rs#L92-L103

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Same here

/// return the new minimum value with appropriate exactness information.
fn set_min_if_lesser(
min_nominee: Precision<ScalarValue>,
min_values: Precision<ScalarValue>,
) -> Precision<ScalarValue> {
match (&min_values, &min_nominee) {
(Precision::Exact(val1), Precision::Exact(val2)) if val1 > val2 => min_nominee,
(Precision::Exact(val1), Precision::Inexact(val2))
| (Precision::Inexact(val1), Precision::Inexact(val2))
| (Precision::Inexact(val1), Precision::Exact(val2))
if val1 > val2 =>
{
min_nominee.to_inexact()
}
(Precision::Exact(_), Precision::Absent) => min_values.to_inexact(),
(Precision::Absent, Precision::Exact(_)) => min_nominee.to_inexact(),
(Precision::Absent, Precision::Inexact(_)) => min_nominee,
(Precision::Absent, Precision::Absent) => Precision::Absent,
_ => min_values,
}
}