FEAT: Add stress test pipeline and migrate it to new 1ES Pool/Images

[gargsaumya]

Work Item / Issue Reference

AB#41877

GitHub Issue: #<ISSUE_NUMBER>

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Summary

This pull request adds a comprehensive suite of multi-threaded stress tests for the mssql-python package. The new tests cover a wide range of concurrency scenarios, sustained load, pool lifecycle, and heavy query scaling to ensure robust performance and stability under high-load conditions. The tests are cross-platform, feature deterministic shutdowns, and include adaptive validation of error rates.

Concurrency and load testing:

• Added a concurrency matrix of tests (test_concurrency_matrix) that runs queries with varying thread counts and connection pooling settings, validating error rates at different concurrency levels.
• Introduced sustained load tests (test_sustained_load) that run multiple threads for extended durations to simulate real-world high-load situations.
• Implemented heavy query scaling tests (test_heavy_query_scaling) with large result sets and high thread counts to stress test the connection pool.

Connection pool management:

• Added a pool lifecycle test (test_pool_lifecycle_cycles) to repeatedly enable and disable connection pooling, verifying deterministic shutdown and resource cleanup.
• Provided utilities for strict thread joining and pool shutdown to ensure clean test teardown and avoid resource leaks.

Test infrastructure and utilities:

• Defined data models (ThreadResult, StressResult) and a runner class (MultiThreadedQueryRunner) for collecting detailed metrics and managing

[Copilot]

Pull request overview

Adds a new scheduled/manual OneBranch pipeline to run stress testing and introduces a new multi-threaded stress test suite for mssql-python aimed at validating pooling and concurrency behavior under sustained and high-concurrency load.

Changes:

• Added a new tests/test_020_multithreaded_stress.py module with multi-threaded stress tests and a helper runner/metrics models.
• Added OneBranchPipelines/stress-test-pipeline.yml to run the stress suite on Windows (LocalDB) and Linux (Docker SQL Server) on a daily schedule or manually.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 12 comments.

File	Description
tests/test_020_multithreaded_stress.py	New concurrency-focused stress tests with a multi-threaded runner and workload scenarios (matrix, sustained load, lifecycle, heavy queries).
OneBranchPipelines/stress-test-pipeline.yml	New scheduled pipeline to provision DBs (LocalDB/Docker) and execute/publish stress + performance stress tests on Windows and Linux agents.

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[gargsaumya]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).