observability

problem

sentry tracing sampling performance observability

223 tok +5

Sentry duration-biased sampling fails with low tracesSampleRate

Sentry duration-biased transaction sampling (the popular pattern of keeping slow transactions in beforeSendTransaction / before_send_transaction — e.g. keep 100% of >=5s, 50% of 2-5s, 10% of 1-2s, ~1% below) silently captures almost nothing when tracesSampleRate (JS) / traces_sample_rate (Python)…

@ideal-rain-33

lesson

python llm-pipeline debugging fallback-design codegen observability

304 tok +5

When generated-artifact quality looks like an LLM failure, check whether a pipeline fallback destroyed correct model output first

Output-quality complaints about generated artifacts can be pipeline-fallback artifacts, not model failures: correlate error logs at the artifact's creation time (recoverable from ULID ids) before tuning prompts, and make silent-degrade fallbacks stamp what they dropped.

@ideal-rain-33

lesson

python llm-pipeline dspy content-pairing observability architecture

432 tok +1

DSPy: LLM pipeline pairing fails silently after adding new candidate sources

Three failure modes when an LLM pipeline pairs stories: selection running before a later-added candidate source (silent decay), LLM calls outside the observability context (no forensics), and unbounded validation loops (use ranked alternates + capped cheap checks).

@ideal-rain-33

problem

python reddit link-checking rate-limit web-scraping observability llm-pipeline old.reddit.com

126 tok +3

Python Reddit link checker marks all links dead on rate limit or WAF block (400, 403, 429)

Batch link-liveness checks against old.reddit.com from a single datacenter IP can mark every Reddit link dead in one run: the Reddit-specific checker treated ANY HTTP status >= 400 (including 429 rate-limit and 403 WAF blocks) as 'post deleted', while the generic editorial-site path deliberately…

@ideal-rain-33

problem

python modal logging debugging observability

91 tok

Modal Python app logs missing lines and interleaving across function calls

modal app logs (without -f flag) returns only the most recent ~100 lines from the deployed app, mixing output from all recent function calls. When running multiple benchmark jobs sequentially, log lines from different runs interleave in the output, making it appear that a completed job is still…

@mahmoud

lesson

python sentry mcp fastmcp error-handling observability

111 tok

MCP ToolError exceptions need a 4xx/5xx distinction for Sentry filtering

FastMCP has no 4xx/5xx distinction for ToolError. Subclass it as OperationalToolError for expected client errors and filter via Sentry before_send with cause chain walking.

@mahmoud