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fix(datagen): make default temporal ranges deterministic #8121

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Merged
westonpace merged 1 commit into from
Jul 31, 2026
Merged

fix(datagen): make default temporal ranges deterministic #8121

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119 changes: 104 additions & 15 deletions rust/lance-datagen/src/generator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2818,14 +2818,29 @@ pub mod array {
Box::new(RandomIntervalGenerator::new(unit))
}

/// The default sampling range for temporal generators: the 365 days ending at
/// 2024-01-01T00:00:00Z (exclusive)
///
/// The range must be a fixed anchor and not derived from the wall clock
/// (e.g. `Utc::now()`), otherwise the same RNG seed would generate different
/// values depending on when the generator was created, breaking
/// reproducibility (e.g. of saved fuzz inputs). Callers that need a
/// time-relative range can use the `*_in_range` variants.
fn default_temporal_range() -> (chrono::DateTime<Utc>, chrono::DateTime<Utc>) {
let end = chrono::DateTime::<Utc>::from_timestamp(1_704_067_200, 0)
.expect("2024-01-01T00:00:00Z is a valid timestamp");
let start = end - chrono::TimeDelta::try_days(365).expect("TimeDelta try_days");
(start, end)
}

/// Create a generator of randomly sampled date32 values
///
/// Instead of sampling the entire range, all values will be drawn from the last year as this
/// is a more common use pattern
/// Instead of sampling the entire range, all values will be drawn from a fixed
/// one-year range (the 365 days ending at 2024-01-01 UTC) as this is a more
/// common use pattern. Use [`rand_date32_in_range`] to control the range.
pub fn rand_date32() -> Box<dyn ArrayGenerator> {
let now = chrono::Utc::now();
let one_year_ago = now - chrono::TimeDelta::try_days(365).expect("TimeDelta try days");
rand_date32_in_range(one_year_ago, now)
let (start, end) = default_temporal_range();
rand_date32_in_range(start, end)
}

/// Create a generator of randomly sampled date32 values in the given range
Expand Down Expand Up @@ -2853,12 +2868,12 @@ pub mod array {

/// Create a generator of randomly sampled date64 values
///
/// Instead of sampling the entire range, all values will be drawn from the last year as this
/// is a more common use pattern
/// Instead of sampling the entire range, all values will be drawn from a fixed
/// one-year range (the 365 days ending at 2024-01-01 UTC) as this is a more
/// common use pattern. Use [`rand_date64_in_range`] to control the range.
pub fn rand_date64() -> Box<dyn ArrayGenerator> {
let now = chrono::Utc::now();
let one_year_ago = now - chrono::TimeDelta::try_days(365).expect("TimeDelta try_days");
rand_date64_in_range(one_year_ago, now)
let (start, end) = default_temporal_range();
rand_date64_in_range(start, end)
}

/// Create a generator of randomly sampled timestamp values in the given range
Expand Down Expand Up @@ -2914,10 +2929,14 @@ pub mod array {
}
}

/// Create a generator of randomly sampled timestamp values
///
/// Instead of sampling the entire range, all values will be drawn from a fixed
/// one-year range (the 365 days ending at 2024-01-01 UTC) as this is a more
/// common use pattern. Use [`rand_timestamp_in_range`] to control the range.
pub fn rand_timestamp(data_type: &DataType) -> Box<dyn ArrayGenerator> {
let now = chrono::Utc::now();
let one_year_ago = now - chrono::Duration::try_days(365).unwrap();
rand_timestamp_in_range(one_year_ago, now, data_type)
let (start, end) = default_temporal_range();
rand_timestamp_in_range(start, end, data_type)
}

/// Create a generator of randomly sampled date64 values
Expand Down Expand Up @@ -3214,8 +3233,12 @@ pub fn rand(schema: &Schema) -> BatchGeneratorBuilder {
#[cfg(test)]
mod tests {

use arrow::datatypes::{Float32Type, Int8Type, Int16Type, UInt32Type};
use arrow_array::{BooleanArray, Float32Array, Int8Array, Int16Array, Int32Array, UInt32Array};
use arrow::datatypes::{Float32Type, Int8Type, Int16Type, TimeUnit, UInt32Type};
use arrow_array::{
BooleanArray, Date32Array, Date64Array, Float32Array, Int8Array, Int16Array, Int32Array,
TimestampMicrosecondArray, TimestampMillisecondArray, TimestampNanosecondArray,
TimestampSecondArray, UInt32Array,
};

use super::*;

Expand Down Expand Up @@ -3395,6 +3418,72 @@ mod tests {
);
}

#[test]
fn test_rng_temporal_deterministic() {
// The default temporal generators must not depend on the wall clock: the
// same seed must produce the same values no matter when the generator is
// created (https://github.com/lance-format/lance/issues/7913). These
// exact values pin both the RNG stream and the fixed default sampling
// range (the 365 days ending at 2024-01-01 UTC).
fn gen_values(mut genn: Box<dyn ArrayGenerator>) -> Arc<dyn Array> {
let mut rng = rand_xoshiro::Xoshiro256PlusPlus::seed_from_u64(DEFAULT_SEED.0);
genn.generate(RowCount::from(3), &mut rng).unwrap()
}

assert_eq!(
*gen_values(array::rand_date32()),
Date32Array::from(vec![19655, 19474, 19717])
);
assert_eq!(
*gen_values(array::rand_date64()),
Date64Array::from(vec![
1_698_192_000_000,
1_682_553_600_000,
1_703_548_800_000
])
);
assert_eq!(
*gen_values(array::rand_timestamp(&DataType::Timestamp(
TimeUnit::Second,
None
))),
TimestampSecondArray::from(vec![1_698_211_127, 1_682_585_540, 1_703_559_286])
);
assert_eq!(
*gen_values(array::rand_timestamp(&DataType::Timestamp(
TimeUnit::Millisecond,
None
))),
TimestampMillisecondArray::from(vec![
1_698_211_127_056,
1_682_585_540_319,
1_703_559_286_487
])
);
assert_eq!(
*gen_values(array::rand_timestamp(&DataType::Timestamp(
TimeUnit::Microsecond,
None
))),
TimestampMicrosecondArray::from(vec![
1_698_211_127_056_596,
1_682_585_540_319_384,
1_703_559_286_487_645
])
);
assert_eq!(
*gen_values(array::rand_timestamp(&DataType::Timestamp(
TimeUnit::Nanosecond,
None
))),
TimestampNanosecondArray::from(vec![
1_698_211_127_056_596_085,
1_682_585_540_319_384_548,
1_703_559_286_487_645_287
])
);
}

#[test]
fn test_rng_list() {
// Note: these tests are heavily dependent on the default seed.
Expand Down
8 changes: 6 additions & 2 deletions rust/lance/tests/query/primitives.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -260,7 +260,9 @@ async fn test_query_date(#[case] data_type: DataType) {
test_scan(&original, &ds).await;
test_take(&original, &ds).await;
test_filter(&original, &ds, "value < current_date()").await;
test_filter(&original, &ds, "value > DATE '2024-01-01'").await;
// Mid-range literal: rand_type samples dates from the fixed range
// [2023-01-01, 2024-01-01), so this splits the generated values
test_filter(&original, &ds, "value > DATE '2023-07-01'").await;
test_filter(&original, &ds, "value is null").await;
test_filter(&original, &ds, "value is not null").await;
})
Expand Down Expand Up @@ -295,7 +297,9 @@ async fn test_query_timestamp(#[case] data_type: DataType) {
test_scan(&original, &ds).await;
test_take(&original, &ds).await;
test_filter(&original, &ds, "value < current_timestamp()").await;
test_filter(&original, &ds, "value > TIMESTAMP '2024-01-01 00:00:00'").await;
// Mid-range literal: rand_type samples timestamps from the fixed range
// [2023-01-01, 2024-01-01), so this splits the generated values
test_filter(&original, &ds, "value > TIMESTAMP '2023-07-01 00:00:00'").await;
test_filter(&original, &ds, "value is null").await;
test_filter(&original, &ds, "value is not null").await;
})
Expand Down
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