Generate UUID sample data in the schema recommender

[xiangfu0]

Summary

The schema recommender's data generator had no support for UUID columns, so recommending a schema containing a UUID column would fail. This adds UUID sample-data generation. Split out from the UUID PR stack as an independent change per review.

Changes

• UuidGenerator (new): generates canonical RFC-4122 UUID strings. The number of distinct values is bounded by the requested cardinality — a fixed random high-order half combined with a low-order counter that cycles [1, cardinality], mirroring StringGenerator. (Values are not version-4; the version/variant bits are not set, which is irrelevant for sample data — they remain canonically-formatted, parseable UUID strings.)
• GeneratorFactory: route DataType.UUID to UuidGenerator.
• AvroSchemaUtil.toAvroSchemaJsonObject: map a UUID column to an Avro string annotated with logicalType: "uuid" (consistent with the original-type approach already used for BOOLEAN and TIMESTAMP) instead of collapsing to raw bytes, so generated sample data round-trips as canonical UUID strings. This is a recommender-only helper with a single caller (AvroWriter); ingestion and segment-conversion Avro mapping are untouched.

Testing

• UuidGeneratorTest: single-value canonical output, cardinality bounding + counter cycling, null-numberOfValuesPerEntry default, multi-value list.
• AvroSchemaUtilTest: UUID → logicalType:uuid string mapping.
• AvroWriterTest: end-to-end round-trip — a UUID column generates, writes to Avro, and reads back as canonical UUID strings.

[Copilot]

Pull request overview

Adds end-to-end UUID support to the schema recommender’s sample-data pipeline by generating UUID values and ensuring the generated Avro schema represents UUID columns as logical-type UUID strings.

Changes:

• Add UuidGenerator and wire DataType.UUID routing in GeneratorFactory.
• Update AvroSchemaUtil.toAvroSchemaJsonObject to emit UUID as Avro string with logicalType: "uuid" (instead of bytes) for recommender-generated Avro.
• Add/extend tests covering UUID schema mapping and Avro round-trip behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pinot-plugins/pinot-input-format/pinot-avro-base/src/test/java/org/apache/pinot/plugin/inputformat/avro/AvroSchemaUtilTest.java	Adds UUID-specific schema assertions for logicalType: "uuid" and updates prior expectations.
pinot-plugins/pinot-input-format/pinot-avro-base/src/main/java/org/apache/pinot/plugin/inputformat/avro/AvroSchemaUtil.java	Maps DataType.UUID to Avro string annotated with logicalType: "uuid" for recommender Avro schema generation.
pinot-controller/src/test/java/org/apache/pinot/controller/recommender/data/writer/AvroWriterTest.java	Adds an end-to-end UUID round-trip test through Avro writing/reading.
pinot-controller/src/test/java/org/apache/pinot/controller/recommender/data/generator/UuidGeneratorTest.java	New unit tests for UUID generation semantics (canonical formatting, cardinality cycling, MV behavior).
pinot-controller/src/main/java/org/apache/pinot/controller/recommender/data/generator/UuidGenerator.java	New generator producing UUID-formatted strings with bounded distinct values.
pinot-controller/src/main/java/org/apache/pinot/controller/recommender/data/generator/GeneratorFactory.java	Routes DataType.UUID to the new UuidGenerator.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.24%. Comparing base (fd772ee) to head (fb6299c).

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18973      +/-   ##
============================================
+ Coverage     65.21%   65.24%   +0.02%     
  Complexity     1405     1405              
============================================
  Files          3418     3419       +1     
  Lines        214651   214678      +27     
  Branches      33922    33924       +2     
============================================
+ Hits         139989   140056      +67     
+ Misses        63356    63318      -38     
+ Partials      11306    11304       -2     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (ø)
java-21	65.24% <100.00%> (+0.02%)	⬆️
temurin	65.24% <100.00%> (+0.02%)	⬆️
unittests	65.23% <100.00%> (+0.02%)	⬆️
unittests1	56.86% <0.00%> (+0.01%)	⬆️
unittests2	37.76% <100.00%> (+0.01%)	⬆️

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[yashmayya]

LGTM. Nicely scoped change.

Verified the key risk — toAvroSchemaJsonObject has exactly one caller (AvroWriter), so the bytes→string(logicalType "uuid") remap stays recommender-only and doesn't touch the ingestion / segment-conversion Avro mapping. The uuid-on-string form is also the spec-correct Avro representation (the uuid logical type must back a string), and since UUID columns previously threw in the generator this only fixes a broken path rather than changing working behavior.

Counter cycling mirrors StringGenerator, the single-value FieldSpec from DataGenerator#buildSpec keeps the scalar Avro schema consistent, and the CSV/segment path in MemoryEstimator converts the canonical string back to bytes fine. Tests cover the round-trip well. 👍

[xiangfu0]

Opened docs follow-up PR: pinot-contrib/pinot-docs#917