[malinjawi]

What changes are proposed in this pull request?

Part of #9003. This is the native half of #13165, split out to make review easier.

Delta's IncrementMetric counts how many rows an expression is evaluated on, and Velox already tracks that per expression (ExprStats::numProcessedRows). This adds the native side of counting it there:

• 32 fixed counter functions, increment_metric_0 to increment_metric_31. Each one is a pass-through, marked non-deterministic so Velox never constant-folds or dictionary-peels it, and without default null behavior so null inputs still count.
• For a plan that calls a counter, WholeStageResultIterator forces operator_track_expression_stats=true and expression.eval_simplified=false after the user's overrides (simplified evaluation doesn't count rows), and exports the counters' processed-row counts with the operator metrics.
• Counters belong in projections only: [GLUTEN-9003][VL] Count Delta's IncrementMetric natively #13165 emits them from Delta's project transformer alone, and Delta's filter transformer strips its counters and credits the filter's output rows. The plan converter fails the plan if a declared counter is not called by any projection, so a misplaced counter can't report a wrong count.

Nothing calls these functions yet, so plans, metric values and the metrics JSON don't change: an operator's metrics get an expressionStats object only when its plan calls a counter. #13358 reads the counts on the JVM side, and #13165 makes the Delta transformers emit the calls.

How was this patch tested?

IncrementMetricFunctionTest: pass-through including nulls; the shapes Delta emits (counters over literals, per-branch counts inside if with the result checked); a dictionary input, which must not be peeled; detecting counters in a plan; rejecting a counter outside a projection; and that the forced configs keep counting when a user sets eval_simplified=true and operator_track_expression_stats=false.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: IBM Bob

[malinjawi]

cc: @zhouyuan @rui-mo @felipepessoto

[Copilot]

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Copilot review overview

4 open issues

• This adds expressionStats to the operator metrics JSON unconditionally (often as an empty… · New
• isIncrementMetricFunction currently treats any name with the increment_metric_ prefix as a… · New
• Plan detection only inspects ProjectNode and FilterNode. If counters ever appear in other plan… · New
• trackExpressionStats_ reads like a direct reflection of the query config, but the comment… · New

What changed in this PR

Adds Velox-native support for Delta’s IncrementMetric by introducing fixed-slot counter functions and wiring their per-expression processed-row counts into operator metrics, while forcing the necessary query config knobs when counters are present in the plan.

Changes:

• Added increment_metric_<slot> (0–31) passthrough vector functions and registration.
• Added plan detection + query-config forcing to ensure expression stats are tracked and simplified eval is disabled when counters are used.
• Exported counter processed-row counts into operator metrics JSON under expressionStats; added unit tests.

File	Description
cpp/​velox/​operators/​functions/​IncrementMetricFunction.h	Declares fixed-slot counter APIs, plan detection, and config overrides.
cpp/​velox/​operators/​functions/​IncrementMetricFunction.cc	Implements counter function registration, counter-name detection, plan traversal, and config override helper.
cpp/​velox/​operators/​functions/​RegistrationAllFunctions.cc	Registers the new counter functions during startup registration.
cpp/​velox/​compute/​WholeStageResultIterator.h	Adds a flag to track whether the plan uses counters (to force configs).
cpp/​velox/​compute/​WholeStageResultIterator.cc	Forces configs when counters are detected; exports counter stats into operator metrics JSON.
cpp/​velox/​tests/​IncrementMetricFunctionTest.cc	Adds tests for passthrough behavior, counting semantics, plan detection, and config-forcing.
cpp/​velox/​tests/​CMakeLists.txt	Adds the new test file to the existing test target.
cpp/​velox/​CMakeLists.txt	Adds the new implementation file to the build.

_{Review effort: Lite}