Add heuristic for max ids of stacked tables.

[hertschuh]

Propagate the max_ids_per_partition and max_unique_ids_per_partition from TableSpecs to StackedTableSpecs by taking the max from the stacked tables.

[gemini-code-assist]

Summary of Changes

Hello @hertschuh, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the handling of StackedTableSpecs within the JAX TPU embedding layer by introducing a robust heuristic for calculating critical ID limits. It ensures that max_ids_per_partition and max_unique_ids_per_partition for stacked tables accurately reflect the maximum requirements of their underlying individual tables, thereby preventing potential issues related to ID capacity and improving the overall stability and correctness of distributed embedding configurations.

Highlights

• Heuristic for Max IDs: Implemented a heuristic to determine the max_ids_per_partition and max_unique_ids_per_partition for StackedTableSpecs.
• Value Propagation: These maximum ID values are now propagated from the individual TableSpecs to their corresponding StackedTableSpecs by taking the maximum value across all tables within a stack.
• Stacked Table Spec Update: The StackedTableSpec instances are updated with these newly calculated maximums, and the stacked_table_spec attribute of each constituent TableSpec is re-linked to the updated stacked spec.

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[gemini-code-assist]

Code Review

This pull request adds a heuristic to propagate max_ids_per_partition and max_unique_ids_per_partition from TableSpecs to StackedTableSpecs. The implementation is correct, but I've suggested a refactoring to improve code clarity and efficiency. The suggestion combines multiple loops and intermediate data structures into a single, more Pythonic dictionary comprehension.

[hertschuh]

@abheesht17 I verified this with the ml-perf example.

[abheesht17]

LGTM, thanks!