Dashboards: let an equation show as a percentage and set its decimal places

[sergical]

This is a more broad feature that we want to solve, to let equations have units / data types other then number. We can either let users hardcode this, have some heuristic to determine it (duration * 2 = duration), or both. It's highly related to EXP-879

What happens

A share is always an equation, and Sentry shows it as a raw number with all its decimals.

Widget query	Shows	Wanted
equation|100 * sum(gen_ai.usage.cache_read.input_tokens) / sum(gen_ai.usage.input_tokens)	83.6758	83.7%
equation|(sum(gen_ai.usage.input_tokens) - sum(gen_ai.usage.cache_read.input_tokens)) / count() (table column)	1,635.3072	1,635

A widget has no setting for the type or the decimal places of an equation, so the only place for "%" is the widget title. Big number thresholds work on the value, but the value still shows without "%".

The prompt cache hit rate is one of the main numbers for AI agent cost, and it is a ratio of two sums.

Expected

One or both of these:

1. A per-column setting on a widget query for an equation: output type (number, percentage, currency, duration) and decimal places.
2. a / b where a and b have the same type is typed as percentage and shows with the existing percentage renderer (formatPercentage in static/app/utils/discover/fieldRenderers.tsx), so users do not need 100 *.

Plain numbers from an equation get a sensible default: at most 2 decimals, or none when the value is above 100.

Steps to reproduce

1. Send spans with gen_ai.usage.input_tokens and gen_ai.usage.cache_read.input_tokens.
2. Make a big number widget with equation|100 * sum(gen_ai.usage.cache_read.input_tokens) / sum(gen_ai.usage.input_tokens).
3. It shows 83.6758, with no %, and there is no setting to change this.

Related

• The unit issue for currency and duration: Dashboards: equations lose the unit of their fields ($, duration) #124678
• get_unit_and_type() in src/sentry/api/bases/organization_events.py returns "number" for every equation except rates (fix(api): Fix rate units not populating for equation fields #108043).

[getsantry]

Assigning to @getsentry/support for routing ⏲️

[linear-code]

ENG-8640

[getsantry]

Routing to @getsentry/product-owners-dashboards for triage ⏲️

[DominikB2014]

@sergical this a feature that has been requested before, i think we would tie this into #121946, we could have the unit save as part of the saved equation.

I think auto inferring unit's is a really cool idea, that's also something we've discussed before. For example if you just multiply a duration unit by a static number, the type should always be a duration. There's probably some heuristic we could use for that, but it probably wouldn't cover all cases, and we would want to be confident it wouldn't break anyone else, so i think having it saved with the equation would be a good first step.