fix(optimizer): Fix bug in partitioning utils

[feilong-liu]

Description

Current isPartitionedOn function will return true when partition columns is empty, it's under the assumption that empty partition columns means no partitioning hence all data in one single node. However this is not the case for arbitrary distribution, where partition columns is empty but data is not in one single node. In this PR, I explicitly check that the partition is single node when partition columns is empty.

Motivation and Context

Bug fix

Impact

Fix a correctness bug

Test Plan

Unit tests

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Release Notes

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== NO RELEASE NOTE ==

Summary by Sourcery

Fix partitioning utility behavior for empty partitioning arguments and strengthen test coverage for partitioning semantics.

Bug Fixes:

• Correct isPartitionedOn to only treat empty partitioning arguments as partitioned when using single-node or coordinator-only distributions.

Tests:

• Add unit tests covering isPartitionedOn behavior across different distribution types, empty arguments, known constants, and matching/non-matching columns.

[sourcery-ai]

Reviewer's Guide

Adjusts PartitioningUtils.isPartitionedOn semantics for empty partitioning arguments to distinguish truly single-node/coordinator-only distributions from multi-node distributions, and adds unit tests to cover the new behavior and existing partitioning scenarios.

Class diagram for updated partitioning types and isPartitionedOn

classDiagram
    class PartitioningUtils {
        +boolean isPartitionedOn(Partitioning partitioning, Collection columns, Set knownConstants)
    }

    class Partitioning {
        +List arguments
        +PartitioningHandle handle
        +List getArguments()
        +PartitioningHandle getHandle()
    }

    class PartitioningHandle {
        +boolean isSingleNode()
        +boolean isCoordinatorOnly()
    }

    class VariableReferenceExpression {
    }

    class RowExpression {
    }

    class Collection_VariableReferenceExpression {
    }

    class Set_VariableReferenceExpression {
    }

    PartitioningUtils --> Partitioning : uses
    PartitioningUtils --> VariableReferenceExpression : uses
    PartitioningUtils --> RowExpression : uses
    Partitioning --> PartitioningHandle : has
    Partitioning --> RowExpression : has arguments
    PartitioningUtils --> PartitioningHandle : checks distribution
    PartitioningUtils --> Collection_VariableReferenceExpression : columns (Collection<VariableReferenceExpression>)
    PartitioningUtils --> Set_VariableReferenceExpression : knownConstants (Set<VariableReferenceExpression>)

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Flow diagram for updated isPartitionedOn partitioning logic

flowchart TD
    A[Start isPartitionedOn] --> B[Read partitioning.arguments]
    B --> C{arguments is empty?}
    C -- Yes --> D[Check partitioning.handle.isSingleNode]
    D --> E[Check partitioning.handle.isCoordinatorOnly]
    E --> F{isSingleNode or isCoordinatorOnly?}
    F -- Yes --> G[Return true]
    F -- No --> H[Return false]
    C -- No --> I[Iterate each RowExpression argument]
    I --> J[Ignore arguments that are constants using knownConstants]
    J --> K[Compare remaining arguments to columns]
    K --> L{All required columns covered by arguments?}
    L -- Yes --> G
    L -- No --> H

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File-Level Changes

Change	Details	Files
Refine isPartitionedOn behavior when partitioning arguments are empty to depend on the partitioning handle rather than assuming single-node semantics.	Add an early return in isPartitionedOn that checks partitioning handles with no arguments and returns true only for single-node or coordinator-only distributions Preserve existing per-argument partitioning checks for cases where partitioning arguments are present	presto-main-base/src/main/java/com/facebook/presto/sql/planner/optimizations/PartitioningUtils.java
Introduce unit test coverage for isPartitionedOn across different distribution handles, argument configurations, and known-constant columns.	Add TestPartitioningUtils class exercising empty-argument behavior for SINGLE, COORDINATOR, HASH, BROADCAST, ARBITRARY, and SOURCE distributions Add tests for matching and non-matching partition columns and for columns treated as known constants Add tests validating that single-node and coordinator distributions report partitioned-on for any requested columns even when partitioning arguments are empty	presto-main-base/src/test/java/com/facebook/presto/sql/planner/optimizations/TestPartitioningUtils.java

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[sourcery-ai]

Hey - I've left some high level feedback:

• Consider adding a short comment in isPartitionedOn above the early return for empty arguments to document why only single-node and coordinator-only partitioning are treated as partitioned in that case, since this is subtle and changes previous behavior.
• The tests in TestPartitioningUtils repeatedly construct VariableReferenceExpression instances in the same way; you could extract a small helper method (e.g., variable(String name)) to reduce duplication and improve readability.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider adding a short comment in `isPartitionedOn` above the early return for empty arguments to document why only single-node and coordinator-only partitioning are treated as partitioned in that case, since this is subtle and changes previous behavior.
- The tests in `TestPartitioningUtils` repeatedly construct `VariableReferenceExpression` instances in the same way; you could extract a small helper method (e.g., `variable(String name)`) to reduce duplication and improve readability.

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