feat: Support Spark expression hours by 0lai0 · Pull Request #3804 · apache/datafusion-comet

0lai0 · 2026-03-27T07:15:00Z

Which issue does this PR close?

Rationale for this change

Comet previously did not support the Spark hours expression (a V2 partition transform).
Queries using the hours function for partitioning would fall back to Spark's JVM execution instead of running natively on DataFusion. By adding native support for this expression, we allow more Spark workloads (especially those partitioned by hourly intervals) to benefit from Comet's native acceleration.

What changes are included in this PR?

This change adds end-to-end native support for the hours partition transform. Since Hours is a PartitionTransformExpression (and not a TimeZoneAwareExpression), the timezone is injected from the session configuration during the planning phase.
The native implementation uses Arrow's unary and try_unary kernels for efficient vectorized computationThe semantics are: hours since Unix epoch (1970-01-01 00:00:00 UTC), computed by floor-dividing the raw microsecond value by 3_600_000_000. Both TimestampType and TimestampNTZType use the same arithmetic — no session timezone offset is applied, since this transform is always UTC-based..

expr.proto: Added HoursTransform message definition to pass the child expression and session timezone.
datetime.scala: Added CometHours serde handler to intercept the Spark Hours expression and read the timezone from SQLConf.
QueryPlanSerde.scala: Registered the CometHours handler in the temporal expressions map.
hours.rs: Added SparkHoursTransform UDF using efficient Arrow kernels.
temporal.rs & expression_registry.rs: Registered the native Builder for the new expression.

How are these changes tested?

Added comprehensive evaluation in both Rust and Scala:

Rust Unit Tests : Added unit tests in hours.rs covering:
- Positive/negative (pre-epoch) epoch handling
- Epoch boundary (zero)
- Timezone offset handling
- Null propagation
- Proper isolation of TimestampNTZType (ensuring it ignores timezone offsets)
```
cargo test -p datafusion-comet-spark-expr -- datetime_funcs::hours
```
Scala Integration Tests: Evaluated end-to-end execution in CometTemporalExpressionSuite.
```
./mvnw test -pl spark -Dsuites='org.apache.comet.CometTemporalExpressionSuite'
```

…ce epoch from timestamps.

parthchandra

The PR text says there is an end-to-end test but there doesn't seem to be any. CometTemporalExpressionSuite is probably the right place to add such a test similar to the "days - timestamp(input)" test.

parthchandra · 2026-04-07T00:41:45Z

native/spark-expr/src/datetime_funcs/hours.rs

+                            )?;
+                            let offset_secs =
+                                tz.offset_from_utc_datetime(&dt).fix().local_minus_utc() as i64;
+                            let local_micros = micros + offset_secs * 1_000_000;


In Spark's corresponding implementation in InMemoryBaseTable it looks like the session timezone is not being applied.
Can you add a unit test that reads from InMemoryBaseTable and compares with the results produced by Spark ?

Sure, thanks @parthchandra for review. I’ll correct it, add the missing test, and update it in the next commit.

PR updated. Thanks!

parthchandra · 2026-04-10T00:46:12Z

native/spark-expr/src/datetime_funcs/hours.rs

+
+        match args {
+            [ColumnarValue::Array(array)] => {
+                let ts_array = as_primitive_array::<TimestampMicrosecondType>(&array);


This should be after the match on array.data_type in the DataType::Timestamp(Microsecond, _) arm. This would panic for other types.

Fixed. Moved the cast inside the DataType::Timestamp(Microsecond,_) to prevent panics on unsupported types.

parthchandra · 2026-04-10T00:48:33Z

native/spark-expr/src/datetime_funcs/hours.rs

+                let result: Int32Array = match array.data_type() {
+                    DataType::Timestamp(Microsecond, _) => {
+                        arrow::compute::kernels::arity::unary(ts_array, |micros| {
+                            micros.div_euclid(MICROS_PER_HOUR) as i32


Why div_euclid? Elsewhere the code is generally using div_floor

Updated to use div_floor to match the rest of the codebase. Thanks for pointing this out!

parthchandra · 2026-04-10T00:54:52Z

spark/src/main/scala/org/apache/comet/serde/datetime.scala

+      binding: Boolean): Option[ExprOuterClass.Expr] = {
+    val childExpr = exprToProtoInternal(expr.child, inputs, binding)
+
+    if (childExpr.isDefined) {


It might be better to explicitly check the child expr datatype and only allow valid types, fall back otherwise.
See CometDays below.

Fixed. Added explicit type checking to only allow TimestampType and TimestampNTZType, and it will now fall back for other types similarly to CometDays.

parthchandra · 2026-04-10T00:58:24Z

spark/src/test/scala/org/apache/comet/CometTemporalExpressionSuite.scala

+        val ts = row.getAs[java.time.LocalDateTime]("ts")
+        val micros = if (ts != null) {
+          org.apache.spark.sql.catalyst.util.DateTimeUtils.localDateTimeToMicros(ts)
+        } else 0L // assuming safe non-null


If the timestamp generated by the generator is null, then hours should return null. This will return 0.

Fixed. It now properly handles null values and returns null instead of 0.

0lai0 · 2026-04-10T09:46:16Z

Thanks to @parthchandra for the review and feedback. PR has been updated.

parthchandra

lgtm. @0lai0 can you resolve the merge conflicts so this can be merged?

0lai0 · 2026-04-11T06:38:54Z

Thanks @parthchandra . Conflicts resolved and PR updated.

0lai0 added 2 commits March 27, 2026 14:50

feat: Add Spark V2 partition transform Hours to calculate hours sin…

f7cf339

…ce epoch from timestamps.

fix style

ebe4073

parthchandra reviewed Apr 7, 2026

View reviewed changes

remove timezone dependency from hours partition

28f3535

parthchandra reviewed Apr 10, 2026

View reviewed changes

fix update hours and support TimestampNTZ type

df0cc64

parthchandra approved these changes Apr 10, 2026

View reviewed changes

0lai0 and others added 2 commits April 11, 2026 14:31

Merge branch 'main' into support_spark_hours

f4f7dca

remove redundant whitespace

7c750f0

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0lai0 commented Mar 27, 2026 • edited by parthchandra Loading Uh oh! There was an error while loading. Please reload this page.

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0lai0 Apr 7, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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0lai0 commented Apr 10, 2026

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0lai0 commented Apr 11, 2026

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0lai0 commented Mar 27, 2026 •

edited by parthchandra

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0lai0 Apr 7, 2026 •

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