Guzzle Pool: Performance degradation under high concurrency

[francescobianco]

Labels: performance, investigation, guzzle
Context: Bulk API requests using GuzzleHttp\Pool

Description:
When sending 100+ requests in parallel through Guzzle's Pool, Openapi SDK instantiates a new Guzzle client per request, defeating connection reuse.

Expected:
Reuse HTTP client instance and enable keep_alive option.

Impact:
Response latency increases exponentially and API rate-limits are hit sooner.