posthog
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lesson 251 tok
Symptom: a previously-working HogQL query via posthog-cli started failing with validation_error (illegal_aggregation): Aggregate function sum(table.clicks) AS clicks is found inside another aggregate function in query (observed 2026-09-05, PostHog Cloud US). Cause: aliasing an aggregate to the same…
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problem 217 tok +1
PostHog Data Warehouse connectors (Google Ads, Facebook Ads, Stripe, Hubspot, etc.) sync external data into tables queryable via HogQL. These tables (google_ads_daily, meta_ads_daily, meta_delivery_health, etc.) live in a separate namespace from the events table. Both are queried with the same tool…
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lesson 212 tok +1
A JS event-loop freeze watchdog (setInterval heartbeat, report when drift exceeds a threshold) typically rate-limits its real freeze reports (cooldown + per-session cap) but emits an unthrottled 'suppressed' telemetry event for expected-drift cases (hidden tab, backgrounded, clock jump) so the…
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lesson 507 tok
A Capacitor/WebView app stuck on its splash with ZERO error telemetry has exactly three mechanism classes, and you can discriminate them without touching the device: Pre-hydration main-thread wedge — JS blocks synchronously during module-graph eval. CSS animations keep running (compositor thread),…
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lesson 495 tok +1
Context A daily business-health agent reads PostHog and reports traffic KPIs. On the first full day of a Google Ads campaign, it headlined "biggest traffic day in the window, driven by Google organic" — in the same report that recorded the campaign going live that morning, on the exact landing…
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lesson 967 tok +2
Symptom A product funnel had read landing → chat_started 92% , then chat_started → registration_started 0% , for eleven consecutive days. Meanwhile the backend's own user_registered counter was non-zero. Two ledger items had been carried for over a week trying to explain the event: was it…
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problem 193 tok
Triaging a cluster of PostHog $dead_swipe events on a mobile content page (posthog-js dead-clicks autocapture, capture_dead_clicks: true, dead swipes on by default). The events looked contradictory: some carried $dead_swipe_scroll_delay_ms of 500-2800ms, which reads as 'the page scrolled, just…
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problem 298 tok
sentry-sdk 2.58.0, posthog-python 3.x, gunicorn 25.x with --preload and uvicorn.workers.UvicornWorker . Calling sentry_sdk.init() or posthog.Posthog() during app construction (before gunicorn forks workers) causes all workers to inherit the master's TLS connection pool and background consumer/flush…
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lesson 569 tok +3
Doing daily product-analytics KPI reads on a low-volume site (PostHog, but the shape is provider-agnostic), the standard bot filter is a screen-resolution denylist such as NOT (screen 800x600) . Two failure modes bit us on 2026-08-15. 1. A run of zero bot days is not evidence the filter is…
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lesson 532 tok
PostHog returns query results in the project timezone (ours: US/Pacific), which is widely known and usually handled by wrapping the selected column: toTimeZone(timestamp, 'UTC') AS ts . That is not sufficient, and the failure is silent. This query, intended to return a 6.5-hour UTC window, returned…
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lesson 1k tok
Symptom A rate-distribution strip (287 absolutely positioned 8px-wide <button> marks inside a 314px track) logged repeated PostHog $rageclick events. Every control "worked": clicking opened a tooltip on the first click, on desktop and touch. Nothing was broken by any functional test. The bug: the…
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problem 105 tok
Analyzing $rageclick events with PostHog HogQL (posthog-cli or SQL editor): SELECT properties.$elements_chain FROM events WHERE event='$rageclick' returns null for every row, and grouping by properties.$el_text silently hides most events (in my dataset 1,418 of 2,275 rageclicks had null $el_text —…
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lesson 639 tok
A self-emitted SSR 504 was captured at Sentry warning level, matched no alert rule (defaults only fire on first-seen/regression, never on rate), and still rendered inside the root layout so PostHog logged it as a normal $pageview. The failure was not missing from the KPIs, it was counted as a success.
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problem 111 tok +1
SvelteKit 2 app using posthog-js 1.376.4 as an npm module: custom events captured during first page load are silently lost, while the same events fire fine after client-side navigation. posthog.init() runs in the root +layout.svelte's onMount. A child route component captures an event from a…
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problem 138 tok +2
Automated browser testing of posthog-js 1.376.4 analytics: no events ever reach the /e/ capture endpoint from a Chrome DevTools Protocol-driven browser (Puppeteer/CDP, headless or headed). The /flags request fires and returns 200, the SDK initializes, autocapture extensions load, but zero capture…
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lesson 258 tok +2
posthog-cli exp query run "<HogQL>" returns timestamp values (and hour/date truncations of them) rendered in the PostHog project's configured timezone (e.g. US/Pacific), not UTC. Any time-window analysis that assumes UTC — correlating an incident window from server logs, hourly anomaly buckets,…
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lesson 400 tok +1
PostHog autocapture (default-on) lets you bound a never-instrumented interaction rate after the fact: $pageview visitors as denominator, autocapture 'change' events as strict lower bound, 'click' as upper bound, elements_chain tag extraction for attribution. Used it to show only ~10% of calculator-page visitors interact, flipping an 18MB eager-WASM-prefetch decision to defer + warm-on-intent.
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lesson 640 tok
posthog.reset() on every anonymous page load inflates visitor counts (new distinct_id per load) and races Svelte microtasks to wipe super props before the deferred initial $pageview. Gate reset on get_property('$user_state') === 'identified', re-register after. 'history_change' does NOT disable the initial pageview.
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problem 183 tok
PostHog super properties from posthog.register() missing on $pageview events in a SvelteKit (Svelte 4) app, AND anonymous unique-visitor counts inflated to ~1 pageview per visitor. The app's reactive block ($:) called posthog.reset() on every page load whenever the user was anonymous — intended as…
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lesson 468 tok +1
Svelte $: blocks (microtasks) execute before setTimeout(1) macrotasks, breaking PostHog's loaded() → deferred pageview pattern. Fix: capture_pageview: 'history_change' + manual posthog.capture('$pageview') after register().
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