[jira] [Assigned] (SPARK-47410) refactor UTF8String and CollationFactory

["Wenchen Fan (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-47410?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wenchen Fan reassigned SPARK-47410:
-----------------------------------

    Assignee: Uroš Bojanić

> refactor UTF8String and CollationFactory
> ----------------------------------------
>
>                 Key: SPARK-47410
>                 URL: https://issues.apache.org/jira/browse/SPARK-47410
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 4.0.0
>            Reporter: Uroš Bojanić
>            Assignee: Uroš Bojanić
>            Priority: Major
>              Labels: pull-request-available
>
> This ticket addresses the need to refactor the {{UTF8String}} and {{CollationFactory}} classes within Spark to enhance support for collation-aware expressions. The goal is to improve code structure, maintainability, readability, and testing coverage for collation-aware Spark SQL expressions.
> The changed introduced herein should simplify addition of new collation-aware operations and ensure consistent testing across the codebase.
>  
> To further support the addition of collation support for new Spark expressions, here are a couple of guidelines to follow:
>  
> // 1. Collation-aware expression implementation
> CollationSupport.java
>  * should serve as a static entry point for collation-aware expressions, providing custom support
>  * for example: one by one Spark expression with corresponding collation support
>  * also note that: CollationAwareUTF8String should be used for collation-aware UTF8String operations & other utility methods
> CollationFactory.java
>  * should continue to serve as a static provider for high-level collation interface
>  * for example: interacting with external ICU components such as Collator, StringSearch, etc.
>  * also note that: no low-level / expression-specific code should generally be found here
> UTF8String.java
>  * should be largely collation-unaware, and generally be used only as storage, nothing else
>  * for example: don’t change this class at all (with the only one-time exception of: semanticEquals/Compare)
>  * also note that: no collation-aware operation implementations (using collationId) should be put here
> stringExpressions.scala / regexpExpressions.scala / other “sql.catalyst.expressions” (for example: Between.scala)
>  * should only contain minimal changes in order to re-route collation-aware implementations to CollationSupport
>  * for example: most changes should be in relation to: adding collationId, using correct data types, replacements, etc.
>  * also note that: nullSafeEval & doGenCode should likely note contain introduce extra branching based on collationId
>  
> // 2. Collation-aware expression testing
> CollationSuite.scala
>  * should be used for testing more general collation concepts
>  * for example: collate/collation expressions, collation names, DDL, casting, aggregate, shuffle, join, etc.
>  * also note that: no extra tests should generally be added
> CollationSupportSuite.java
>  * should be used for expression unit tests, these tests should be as rigorous as possible in order to cover various cases
>  * for example: unit tests that test collation-aware expression implementation for various collations (binary, lowercase, ICU)
>  * also note that: these tests should generally be written after adding appropriate expression support in CollationSupport.java
> CollationStringExpressionsSuite.scala / CollationRegexpExpressionsSuite.scala / CollationExpressionSuite.scala
>  * should be used for expression end-to-end tests, these tests should only cover crucial expression behaviour
>  * for example: SQL tests that verify query execution results, expected return data types, casting, unsupported collation handling, etc.
>  * also note that: these tests should generally be written after enabling appropriate expression support in stringExpressions.scala
>  
> // 3. Closing notes
>  * Carefully think about performance implications of newly added custom collation-aware expression implementation
>  * for example: be very careful with extra string allocations (UTF8Strings -> (Java) String -> UTF8Strings, etc.)
>  * also note that: some operations introduce very heavy performance penalties (we should avoid the ones we can)
>  
>  * Make sure to test all newly added expressions and completely (unit tests, end-to-end tests, etc.)
>  * for example: consider edge, such as: empty strings, uppercase and lowercase mix, different byte-length chars, etc.
>  * also note that: all similar tests should be uniform & readable and be kept in one place for various expressions
>  
>  * Consider how new expressions interact with the rest of the system (casting; collation support level - use correct AbstractStringType, etc.)
>  * for example: we should watch out for casting, test it thoroughly, and use CollationTypeCasts if needed for new expressions
>  * also note that: some expressions won’t support all collation types, so that should be clearly reflected in tests and dataTypes



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