[lake/paimon] Compare paimon schema and Fluss schema before alter table.

[loserwang1024]

Purpose

Linked issue: close #2330

Brief change log

Tests

API and Format

Documentation

[Copilot]

Pull request overview

This pull request enhances the Paimon lake catalog integration by comparing Paimon and Fluss schemas before altering tables. This prevents schema inconsistencies that can occur when a previous alter operation partially succeeds (e.g., Paimon succeeds but Fluss fails).

Key Changes:

• Added getFlussSchema() method to LakeCatalog.Context interface to provide current Fluss schema during alter operations
• Implemented schema validation logic in PaimonLakeCatalog to detect and handle schema mismatches between Paimon and Fluss
• Updated MetadataManager and CoordinatorService to pass schema information via the context

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
fluss-common/src/main/java/org/apache/fluss/lake/lakestorage/LakeCatalog.java	Added getFlussSchema() method to Context interface
fluss-common/src/test/java/org/apache/fluss/lake/lakestorage/TestingLakeCatalogContext.java	Updated test context to support schema parameter
fluss-server/src/main/java/org/apache/fluss/server/coordinator/CoordinatorService.java	Updated to create context with schema, and pass FlussPrincipal instead of pre-created context
fluss-server/src/main/java/org/apache/fluss/server/coordinator/MetadataManager.java	Changed method signatures to accept FlussPrincipal and create context locally with current schema
fluss-lake/fluss-lake-paimon/src/main/java/org/apache/fluss/lake/paimon/PaimonLakeCatalog.java	Added schema comparison logic to detect and handle retry scenarios
fluss-lake/fluss-lake-paimon/src/test/java/org/apache/fluss/lake/paimon/PaimonLakeCatalogTest.java	Enhanced tests to cover schema mismatch scenarios and retry logic

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[beryllw]

Maybe we could perform this check earlier—it’s not related to the existing Paimon schema. Also, it’s already validated here:

fluss/fluss-server/src/main/java/org/apache/fluss/server/coordinator/SchemaUpdate.java

Lines 101 to 104 in 256bd7f

	TableChange.ColumnPosition position = addColumn.getPosition();
	if (position != TableChange.ColumnPosition.last()) {
	throw new IllegalArgumentException("Only support addColumn column at last now.");
	}

[loserwang1024]

@beryllw

It’s not related to the existing Paimon schema

If paimon schema is same as fluss schema, all the operations(both add column and set config) can be accepted. Otherwise, only add columns can be accepted to make the schema same.