chore(spanner): add initial setup for built-in metrics

[olavloite]

Sets up the initial boiler-plate code for adding built-in metrics for Spanner.

The feature is hidden behind a feature flag, meaning that it is currently invisible to customers.

[gemini-code-assist]

Code Review

This pull request introduces an experimental built-in metrics and observability framework for the Spanner client, adding dependencies on google-cloud-monitoring-v3 and opentelemetry to trace database operations. The reviewer feedback focuses on managing these new dependencies via cfg(google_cloud_unstable_tracing) flags instead of standard Cargo features to prevent dependency bloat, and conditionally compiling the observability module. Additionally, the reviewer recommends optimizing performance by using &'static str for method names to avoid unnecessary string allocations, and improving the robustness of the Server-Timing header parser to handle parameters in any order, along with adding corresponding test cases.

[codecov]

Codecov Report

❌ Patch coverage is 81.11888% with 54 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.63%. Comparing base (187952a) to head (f599240).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/spanner/src/observability/metrics.rs	72.72%	48 Missing ⚠️
src/spanner/src/observability/exporter.rs	71.42%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5967      +/-   ##
==========================================
- Coverage   97.71%   97.63%   -0.09%     
==========================================
  Files         242      244       +2     
  Lines       60976    61243     +267     
==========================================
+ Hits        59582    59792     +210     
- Misses       1394     1451      +57     

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[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces observability and metrics support to the Spanner client, integrating OpenTelemetry and exporting metrics to Google Cloud Monitoring under the google_cloud_unstable_tracing feature flag. The review feedback highlights critical compilation errors in metrics.rs regarding universe_domain cloning and tonic::Status code retrieval, as well as a potential lifetime issue in the define_idempotent_rpc macro closure. Additionally, improvements are suggested to preserve universe domain resolution by not hardcoding the monitoring endpoint, use the crate name for the meter, enhance readability in server timing parsing, and adhere to the repository's 'return early' style guide in parse_project_id.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces observability and metrics tracking to the Spanner client using OpenTelemetry and Google Cloud Monitoring. It adds a new observability module, defines Spanner-specific metrics (such as operation and attempt latencies), and integrates these metrics across various transactions and client operations. The review feedback suggests optimizing environment variable parsing in metrics.rs by using eq_ignore_ascii_case instead of to_lowercase() to avoid unnecessary string allocations.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces observability and metrics tracking to the Spanner client under the google_cloud_unstable_tracing feature flag, integrating OpenTelemetry and Google Cloud Monitoring to record operation and attempt latencies. The review feedback highlights a critical compilation error in the status-to-string mapping due to private tonic::Status fields and a missing name() method on tonic::Code. Additionally, it is recommended to propagate more configuration options, such as the emulator endpoint, from ClientConfig when initializing the monitoring service.

[olavloite]

/gemini review

[gemini-code-assist]

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[olavloite]

/gemini review

[gemini-code-assist]

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[olavloite]

/gemini review

[gemini-code-assist]

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