[PR] Catalog Migrator: Add Iceberg view migration support [polaris-tools]

["ajantha-bhat (via GitHub)" <gi...@apache.org>]

ajantha-bhat opened a new pull request, #265:
URL: https://github.com/apache/polaris-tools/pull/265

   ## Summary
   
   Adds Iceberg view migration support to the Iceberg Catalog Migrator.
   
   The migrator now supports migrating both Iceberg tables and Iceberg views from a source catalog to a target catalog without copying data. View migration uses the new Iceberg `ViewCatalog.registerView` support added in Iceberg 1.11.0, which registers a view in the target catalog from the source view metadata location.
   
   By default, the `migrate` command now migrates both tables and views when both source and target catalogs support Iceberg views. Existing table-only selector behavior is preserved for users who explicitly provide table selectors.
   
   ## New Options
   
   Adds view selector options to the `migrate` command:
   
   | Option | Description |
   |---|---|
   | `--view-identifiers` | Comma-separated list of view identifiers to migrate |
   | `--view-identifiers-from-file` | File containing one view identifier per line |
   | `--view-identifiers-regex` | Regex used to select matching view identifiers |
   
   Selector behavior:
   
   | Table selector | View selector | What happens |
   |---|---|---|
   | Not specified | Not specified | Migrates **all tables** and **all views** |
   | Specified | Not specified | Migrates **selected tables only**, no views |
   | Not specified | Specified | Migrates **selected views only**, no tables |
   | Specified | Specified | Migrates **selected tables** and **selected views** |
   
   ## Why Views Are Supported Only With `migrate`
   
   View support is intentionally added only to the `migrate` command, not the `register` command.
   
   For tables, `register` can leave the table entry in both source and target catalogs. That is already risky and documented, but table cleanup can use `dropTable(..., purge=false)` when migrating so only the catalog entry is removed from the source.
   
   Iceberg views do not have an equivalent purge-false delete operation. Dropping a view is a lightweight catalog operation, so view migration must delete the successfully migrated view from the source catalog after registering it in the target catalog. Because of that, view migration requires `migrate` semantics and is rejected for `register`.
   
   ## Notes
   
   - View migration runs only when both source and target catalogs implement Iceberg view support.
   - Table migration and view migration are tracked independently in the result summary.
   - Failures for tables or views are reported separately, and failed identifiers can be retried using the existing table selector options or the new view selector options.
   - Documentation and examples are updated to show table and view migration usage.


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Re: [PR] Catalog Migrator: Add Iceberg view migration support [polaris-tools]

["ajantha-bhat (via GitHub)" <gi...@apache.org>]

ajantha-bhat commented on PR #265:
URL: https://github.com/apache/polaris-tools/pull/265#issuecomment-5240356717

   @dimas-b: Please take a look when you have time. Thanks.  


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Re: [PR] Catalog Migrator: Add Iceberg view migration support [polaris-tools]

["ajantha-bhat (via GitHub)" <gi...@apache.org>]

ajantha-bhat merged PR #265:
URL: https://github.com/apache/polaris-tools/pull/265


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