channel pool metric prototype

[scotthart]

No description provided.

[gemini-code-assist]

Code Review

This pull request introduces tracking for outstanding RPCs on selected channels within the Bigtable client's connection pool. It updates the BigtableStub interface and its decorators to accept an OperationContext parameter across all synchronous and asynchronous RPC methods. Additionally, it renames ResourceLabels and DataLabels to TableResourceLabels and TableDataLabels respectively, while introducing ClientResourceLabels and the OutstandingRpcs metric. Feedback on the changes suggests simplifying the label filtering logic in metrics.cc by replacing a complex std::set_difference call with a simpler loop, adhering to the repository's "Reject 'Code Poetry'" style guide principle.

[gemini-code-assist]

Reject "Code Poetry": Simplify Label Filtering

The data map contains exactly 3 elements. Using std::set_difference with a custom Compare struct is overly complex for filtering such a small number of elements.

Per the repository style guide (Reject "Code Poetry"), we should prefer simplicity over cleverness. A simple loop checking if each key is in filtered_data_labels is much easier to read, maintain, and is likely more performant by avoiding the overhead of std::set_difference and custom comparators.

  for (auto const& kv : data) {
    if (filtered_data_labels.find(kv.first) == filtered_data_labels.end()) {
      labels.insert(kv);
    }
  }

References

1. Reject "Code Poetry": Dismantle complex abstractions used for simple tasks. Prefer simplicity over cleverness. ^(link)

[codecov]

Codecov Report

❌ Patch coverage is 75.86207% with 112 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.27%. Comparing base (acf90c3) to head (7587a31).

Files with missing lines	Patch %	Lines
...d/bigtable/tests/observability_integration_test.cc	7.79%	71 Missing ⚠️
...oud/bigtable/internal/operation_context_factory.cc	77.94%	15 Missing ⚠️
google/cloud/bigtable/internal/metrics.cc	79.31%	12 Missing ⚠️
...e/cloud/bigtable/internal/grpc_metrics_exporter.cc	81.08%	7 Missing ⚠️
...oud/bigtable/internal/data_connection_impl_test.cc	95.89%	3 Missing ⚠️
...gle/cloud/bigtable/internal/dynamic_channel_pool.h	91.30%	2 Missing ⚠️
google/cloud/bigtable/internal/metrics.h	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16324      +/-   ##
==========================================
+ Coverage   92.24%   92.27%   +0.03%     
==========================================
  Files        2227     2227              
  Lines      209543   209711     +168     
==========================================
+ Hits       193284   193516     +232     
+ Misses      16259    16195      -64     

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