[claudevdm]

Threads a destination-table key through the AddFiles registration chain, holding the key
constant at the configured table.

stage	before	after
ReadFooterSchema	DoFn<String, SchemaGroup>	DoFn<KV<String,String>, KV<String,SchemaGroup>>
ConvertToDataFile	DoFn<String, SerializableDataFile>	DoFn<KV<String,String>, KV<String,SerializableDataFile>>
CreateManifests	keyed by specId	keyed by KV<table, specId>
CommitManifestFilesDoFn	identifier field	batch.getKey()

AddFiles.expand supplies the constant with
WithKeys.<String,String>of(tableIdentifier), and distinctSchemas drops the key again so
its global combine and the commit path downstream are untouched.

Reviewable as six steps, in this order:

1. key the footer read, add the fileSchemas helper
2. key its two test helpers
3. the converter's cached table becomes a ConcurrentMap<String, TableState>, name still constant
4. key the converter; identifier and its constructor parameters are deleted
5. the manifest key becomes KV<table, specId>
6. the committer reads its table from the key

[claudevdm]

R: @ahmedabu98

[github-actions]

📋 Review Summary

This PR cleanly threads a destination-table key (String) through the AddFiles registration pipeline (ReadFooterSchema, ConvertToDataFile, CreateManifests, and CommitManifestFilesDoFn) in preparation for dynamic table destinations. The refactoring preserves existing single-table behavior by attaching a constant table key via WithKeys and dropping it before the global schema combination step.

🔍 General Feedback

• Thread-safety in ConvertToDataFile is well-maintained by transitioning the single-table state fields into a per-table TableState object managed in a ConcurrentMap, with synchronization and refresh flags scoped per table.
• Coders and key types are properly configured across all modified PCollection stages and unit test helpers.

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[github-actions]

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[ahmedabu98]

LGTM, just a couple suggestions

[ahmedabu98]

This breaks update and upgrade compatibility right?
I think it might be unavoidable, but please mention it in CHANGES.md

[ahmedabu98]

nit: for this and below, can we use an Autovalue/Row type (containing destination and specID) instead of KV<String, Integer>?

Will make it more readable and also give us flexibility to add more columns in the future without breaking update compatibility

[claudevdm]

Sure will mention in CHANGES.md, but I don't think breaking update compat is a big deal for AddFiles. It is a temporary migration transform that is highly unlikely to be updated in place.

[ahmedabu98]

We're turning it into a Managed transform (#40827) so will also need to be wary of upgrade incompatible changes (e.g. a graph change from 2.77 to upgraded 2.79)

The current multi-table changes should be fine though, since Managed transform will come in 2.78 too