Support querying system tables in paimon-cpp

[suxiaogang223]

According to the official Paimon docs, system tables are first-class query interfaces for table metadata, changelog analysis, and catalog-wide observability:
https://paimon.apache.org/docs/master/concepts/system-tables/

paimon-cpp currently lacks system table query support.
This request is to add system table query support in paimon-cpp, including:

• Data system tables (for example):
  snapshots, schemas, options, audit_log, binlog, ro, files, tags, branches, consumers, manifests, aggregation_fields, partitions, buckets, statistics, table_indexes
• Global system tables under sys (for example):
  tables, partitions, all_table_options, catalog_options

Expected outcome:

• Users can query system tables in C++ environments with behavior aligned to Paimon documentation.
• Core changelog observability use cases (including audit_log and binlog) are covered.
• Metadata and global catalog inspection via system tables are available in paimon-cpp.

[lxy-9602]

Very useful issue — thank you!

The system table part overlaps with catalog logic, so we can wait until the catalog refactor (#84 , #92 ) is complete before moving forward. Changelog support isn't available in paimon-cpp yet, but this would be a great addition.

Would you be open to contributing this feature? We’re happy to help with design and review.

[suxiaogang223]

Hi, thanks for the kind feedback!

I’d be happy to contribute this feature. I’ll start by drafting an implementation/design document so we can align on the approach first. Looking forward to your feedback and guidance during the process.

Thanks again!

[suxiaogang223]

I’d like to start with a conservative phased implementation, keeping the first PR small and leaving room for design adjustments.

TODO:

• Add a lightweight system table routing layer for read-only system tables.
• First support metadata-oriented system tables that can be built from existing catalog, schema, snapshot, tag, branch, and manifest metadata.
• Add audit_log and binlog after the changelog read path is clarified and supported.
• Add global sys tables after the catalog interface, especially REST catalog support, is stable enough.
• Keep system tables read-only and align schemas/behavior with Apache Paimon documentation as much as possible.

This should let us deliver useful metadata observability first, while avoiding over-specifying details that may change during implementation.