feat: Mutations Batcher shim

[gkevinzheng]

Changes Made:

• Replaced mutations batcher implementation with one based off of the data client.
• Reworked unit tests.
• Added additional system tests.

[gemini-code-assist]

Summary of Changes

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This pull request refactors the MutationsBatcher to act as a shim, delegating its core batching responsibilities to an internal batcher provided by the data client. This change streamlines the batching mechanism, leveraging the data client's capabilities for more robust and efficient mutation operations, while maintaining the existing public interface.

Highlights

• Mutations Batcher Implementation: The underlying implementation of the Mutations Batcher has been replaced with one based on the new data client, simplifying the batching logic.
• Unit Tests Reworked: Existing unit tests have been refactored to align with the new batcher implementation and improve testability.
• System Tests Added: New system tests have been introduced to cover exception handling and manual flushing scenarios for the Mutations Batcher.

Changelog

• google/cloud/bigtable/batcher.py
  • Removed deprecated internal batching classes and methods, including _MutationsBatchQueue, _BatchInfo, _FlowControl, _flush_async, and related helpers.
  • Updated imports to utilize MutationsExceptionGroup and RowMutationEntry from the google.cloud.bigtable.data module.
  • Modified the MutationsBatcher constructor to initialize and manage an internal batcher instance from table._table_impl.mutations_batcher.
  • Implemented _init_batcher and _close_batcher methods to control the lifecycle and exception handling of the internal batcher.
  • Updated the mutate method to append mutations directly to the new internal batcher.
  • Refactored the flush method to close and re-initialize the internal batcher, ensuring pending mutations are processed.
  • Adjusted the close method to properly shut down the internal batcher and collect any exceptions.
• google/cloud/bigtable/data/_async/client.py
  • Removed unused Callable and status_pb2 imports.
• google/cloud/bigtable/data/_async/mutations_batcher.py
  • Removed unused Callable and Optional imports.
• tests/system/v2_client/test_data_api.py
  • Added test_mutations_batcher_exceptions to verify the batcher's error propagation and handling.
  • Added test_mutations_batcher_manual_flush to confirm correct behavior when manually flushing mutations.
• tests/unit/v2_client/test_batcher.py
  • Refactored unit tests to use _setup_batcher and _atexit_mock fixtures for improved test setup and isolation.
  • Updated constructor tests to verify the correct initialization parameters are passed to the internal batcher.
  • Modified tests for mutate_rows, mutate, flush, and close to assert interactions with the mocked internal batcher operations.
  • Updated exception handling tests to reflect the new MutationsExceptionGroup and FailedMutationEntryError types.
  • Removed obsolete test helper classes and functions related to the old batcher implementation.

Activity

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[gemini-code-assist]

Code Review

The pull request successfully refactors the MutationsBatcher to leverage the new data client's batching capabilities. This significantly simplifies the batcher.py file by removing a substantial amount of custom queueing, flow control, and asynchronous flushing logic. The updated unit and system tests adequately cover the new implementation, including exception handling and manual flushing behavior. The changes align with the goal of migrating to the new data client.

[gemini-code-assist]

Accessing the private attribute _user_batch_completed_callback of the underlying _batcher can introduce fragility. If the internal implementation of the data client's batcher changes this private attribute, it could break this shim. Consider if there's a public API or a more robust way to pass this callback to the underlying batcher, or add a comment explaining this design choice and its implications for future maintenance.