felipepessoto opened a new issue, #12538:
URL: https://github.com/apache/gluten/issues/12538
### Backend
VL (Velox)
### Bug description
When Gluten collects Delta write statistics, `GlutenDeltaJobStatsTracker`
builds a small local Velox aggregation plan and **assumes the offload always
succeeds**, i.e. that the transformed plan is always a `WholeStageTransformer`.
When the stats expression references a data type / expression that Velox does
not yet support (for example `TIMESTAMP_NTZ`), offload validation correctly
rejects the plan and it stays a vanilla Spark `ProjectExec`. The unconditional
cast to `WholeStageTransformer` then throws a `ClassCastException`, failing the
whole write.
**Expected behavior:** an unsupported type/expression in the Delta stats
plan should induce a *fallback* to Spark's native Delta stats collection (the
`DeltaJobStatisticsTracker` delegate path), not crash the write.
**Actual behavior:** the write task fails with:
```
java.lang.ClassCastException: class
org.apache.spark.sql.execution.ProjectExec cannot be cast
to class org.apache.gluten.execution.WholeStageTransformer
at
org.apache.spark.sql.delta.stats.GlutenDeltaJobStatsTracker$GlutenDeltaTaskStatsTracker.<init>(GlutenDeltaJobStatsTracker.scala:174)
at
org.apache.spark.sql.delta.stats.GlutenDeltaJobStatsTracker.newTaskInstance(GlutenDeltaJobStatsTracker.scala:80)
at
org.apache.spark.sql.execution.datasources.FileFormatDataWriter.$anonfun$statsTrackers$1(FileFormatDataWriter.scala:63)
at scala.collection.immutable.List.map(List.scala:236)
```
### Root cause
In `GlutenDeltaTaskStatsTracker` the transform result is cast
unconditionally:
```scala
val veloxTransformer = transformRule(projOp)
val wholeStageTransformer =
ColumnarCollapseTransformStages(config)(veloxTransformer)
.asInstanceOf[WholeStageTransformer] // <-- throws when offload was
rejected
.child
.asInstanceOf[TransformSupport]
```
`transformRule` runs the offload heuristic with a validator. If the stats
expression contains something Velox can't handle (e.g. `TIMESTAMP_NTZ` in an
aggregate/function), the validator rejects offload and `transformRule` returns
the original vanilla `ProjectExec`. `ColumnarCollapseTransformStages` then
leaves it as-is, and `.asInstanceOf[WholeStageTransformer]` fails.
This affects both source variants:
-
`backends-velox/src-delta40/main/scala/org/apache/spark/sql/delta/stats/GlutenDeltaJobStatsTracker.scala`
(~line 174-177)
-
`backends-velox/src-delta33/main/scala/org/apache/spark/sql/delta/stats/GlutenDeltaJobStatsTracker.scala`
(~line 170-173)
### How to reproduce
Run the Delta Spark UTs on the Gluten Velox bundle (as in #12388). Any test
that collects Delta statistics on a `TIMESTAMP_NTZ` column reproduces it, e.g.:
- `data skipping on TIMESTAMP_NTZ`
- `recompute stats multiple columns and files`
More generally: create/write a Delta table whose statistics columns include
a type not yet offloadable by Velox and trigger stats collection.
### Proposed fix
Per the discussion in #12388, rather than fixing `TIMESTAMP_NTZ` support
itself (tracked separately in #11622), make the Gluten Delta stats path
**detect a rejected/failed offload and fall back** to the native
`DeltaJobStatisticsTracker` (or the existing fallback tracker) instead of
assuming a `WholeStageTransformer`. Unsupported operations should induce a
fallback for Delta plans generally.
### Gluten version
main branch
### Spark version
spark-4.0.x and later (reproduced on the Delta pipeline running Spark 4.1 /
Delta v4.2.0; the same unchecked cast exists in the Delta 3.3 source variant).
### References
- PR: #12388 (Delta Spark UT pipeline; this failure is a baseline entry)
- Maintainer discussion:
https://github.com/apache/gluten/pull/12388#issuecomment-4979728602 and
https://github.com/apache/gluten/pull/12388#issuecomment-4989409743
- Related type-support issue: #11622 ([VL] Support TIMESTAMP_NTZ Type)
_This issue was written with the assistance of AI tooling (GitHub Copilot
CLI)._
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