fix(Spanner): Segregate spanner instances for templates in load test.

[pratickchokhani]

• When spanner instances are randomly selected, then 2 load tests across templates can be assigned same instances.
• This can cause the spanner instance to overload.
• Hence, every template is assigned 1 spanner instance.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.89%. Comparing base (14ff8d6) to head (7e55d5f).

Files with missing lines	Patch %	Lines
...he/beam/it/gcp/spanner/SpannerResourceManager.java	0.00%	6 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@              Coverage Diff              @@
##               main    #4136       +/-   ##
=============================================
+ Coverage     33.89%   55.89%   +21.99%     
- Complexity      503     7475     +6972     
=============================================
  Files           215     1134      +919     
  Lines         13128    70126    +56998     
  Branches       1303     8012     +6709     
=============================================
+ Hits           4450    39197    +34747     
- Misses         8313    28383    +20070     
- Partials        365     2546     +2181     

Components	Coverage Δ
spanner-templates	84.63% <ø> (∅)
spanner-import-export	68.92% <ø> (∅)
spanner-live-forward-migration	88.66% <ø> (∅)
spanner-live-reverse-replication	81.26% <ø> (∅)
spanner-bulk-migration	89.06% <ø> (∅)
gcs-spanner-dv	87.85% <ø> (∅)

Files with missing lines	Coverage Δ
...he/beam/it/gcp/spanner/SpannerResourceManager.java	64.72% <0.00%> (-0.96%)	⬇️

... and 944 files with indirect coverage changes

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[gemini-code-assist]

Summary of Changes

Hello, 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 introduces a mechanism to segregate Spanner instances across different load test templates. By allowing tests to specify an instance hint, the system can deterministically assign unique Spanner instances from the available pool, preventing resource contention and potential overloading that occurred when instances were selected randomly.

Highlights

• Spanner Instance Segregation: Updated the Spanner resource manager to allow providing an optional instance hint, ensuring that different load test templates are assigned unique Spanner instances to prevent overloading.
• Resource Manager API Update: Modified the maybeUseStaticInstance method to accept an Optional<Integer> hint, which is used to select a specific instance from the available pool via modulo arithmetic.
• Load Test Configuration: Updated various load test base classes and implementations to pass specific instance hints, effectively segregating resources across different test suites.

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[gemini-code-assist]

Code Review

This pull request updates SpannerResourceManager to allow selecting a static Spanner instance deterministically by passing an optional instanceHint (as Optional<Integer>). It also updates various load-testing classes to use this new parameter. The reviewer suggests simplifying the API usage across all test files by allowing a primitive int to be passed directly instead of wrapping it in java.util.Optional.of(...).

[darshan-sj]

Looks good