(DOCS) Document Custom Performance Metrics

[smeubank]

Intro:

Developers wishing to collect custom performance metrics,
will need some documentation explaining how to use it and some example implementation,
so that they can send these metrics to Sentry and visualize them in product

Checklist:

• start with JS browser setMeasurements
• intro
  • what is it, and what is it not?
  • differentiate between built-in measurements and custom measurements
• how does it work - high level - set (singular, plural, types etc) and attach to transaction
  • public setMeasurement(name: string, value: number, unit: MeasurementUnit = ''): void { this._measurements[name] = { value, unit };
• how to use it
• example snippets
• ensure we cover the boundaries in which they can collect custom metrics
• ideally reference product docs for DnD features where developers could visualize these docs
  • Metrics and Custom Performance Measurements TBA

Related:

• ref(measurements): Make setMeasurement public API sentry-javascript#4933
• feat(types): Add type for measurement unit sentry-javascript#5313

follow up

• needs developer docs
• platforms where it is not supported?

[getsentry-release]

Routing to @getsentry/team-web-sdk-frontend for triage. ⏲️

[AbhiPrasad]

As per https://develop.sentry.dev/sdk/event-payloads/transaction/

Do we need to differentiate between built-in measurements and custom measurements? Do we mention the limit we have on custom measurements?

Optional. An object containing standard/custom measurements with keys signifying the name of the measurement.

https://github.com/getsentry/sentry/blob/a8c960a933d2ded5225841573d8fc426a482ca9c/static/app/utils/discover/fields.tsx#L654-L676

Units: https://getsentry.github.io/relay/relay_metrics/enum.MetricUnit.html

[smeubank]

Do we need to differentiate between built-in measurements and custom measurements?

Yes, the difference should be explained. I will update checklist item 2

Do we mention the limit we have on custom measurements?

Yes we can mention it, but this limit is not set in the SDK if memory serves well. So I would lean towards stating something along the lines of "there is a server side limit, initially set to X (i think it's 20 or 5?)" and not really a need to get more detailed than that

[smeubank]

where do we think these belong in docs? Under enriching events?

https://docs.sentry.io/platforms/javascript/enriching-events/

[AbhiPrasad]

These are part of performance monitoring, so I would say https://docs.sentry.io/platforms/javascript/performance/ or similar. Think it should be under the instrumentation section: https://docs.sentry.io/platforms/javascript/performance/instrumentation/