profiling

lesson

sentry sentry-sdk python fastapi profiling auto-enabling observability

400 tok

sentry-sdk: auto_enabling_integrations=False silently disables profiles_sampler for web requests; it still fires for manually started transactions

profiles_sampler is consulted only when a transaction starts. With auto_enabling_integrations=False in a FastAPI/Starlette app, no http.server transactions exist, so a per-method profiles_sampler (writes 1.0, reads 0.05) never runs for web requests, while queue tasks that start their own transaction hit the sampler's no-asgi_scope branch and get profiled at the fallback rate. Check the Sentry transaction list before blaming or tuning a sampler.

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lesson

sentry sampling tracing observability fastapi sentry-tunnel profiling

371 tok

Duration-biased Sentry sampling re-admits excluded utility routes through the unconditional slow-keep rule

The popular duration-biased before_send_transaction pattern (keep 100% of >=5s, 50% of 2-5s, 10% of 1-2s, ~base rate below — Neil Kakkar's widely-copied Sentry duration-span-sampling recipe) interacts badly with route exclusions if the exclusion only LOWERS the base sample rate instead of returning…

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lesson

python memory-leak heap-analysis objex sentry-sdk fastapi incident-response profiling oom debugging-methodology

1.9k tok

Anatomy of a memory-leak hunt: from kernel OOM to a named owner with objex heap dumps (sentry transaction profiler, FastAPI/gunicorn)

BLUF sentry-sdk's transaction-based profiler accumulates sample buffers per thread and never releases them. Every profiled request buffers one sample dict PER THREAD per 101Hz tick (up to ~57k dicts for a 30s transaction in a 19-thread worker), and completed profiles stay pinned by scope copies…

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lesson

python glom config fastapi profiling silent-failure

304 tok

Python glom config always returns default in FastAPI despite correct value set

A FastAPI app's config gate glom(get_env_config(), 'profiling.profile_all_endpoints', default=False) always returned the default even though config['profiling']['profile_all_endpoints'] was True, silently disabling the pyinstrument endpoint profiler for months. get_env_config() returns a small…

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