# Response times and cost

> See roughly how long requests take where traffic starts, how much of it fails, and what the map costs to run, while a scenario plays, and what a fix does to each.

A fix that stops an outage is easy to want. The question that follows is always “what will it cost, and will it slow anything down?” While a [scenario](https://docs.flozu.app/guides/scenarios.md) plays, Flozu estimates three things to answer it: how long requests take where traffic starts, how much of that traffic fails, and what the map costs to run.

On the **Checkout system** map on Black Friday, shoppers’ requests take about 39 ms, and 95% are done within about 78 ms. Give its parts running costs, as [Make the case for a fix](https://docs.flozu.app/walkthroughs/make-the-case.md) does, try a standby region for Region down, and the comparison says: “After, nobody notices, for about $1,241 a month more.” That’s a decision you can take to your team.

These are estimates, worked out from the map by [fixed rules](https://docs.flozu.app/concepts/how-traffic-is-worked-out.md#estimates), so they’re a guide for comparing one design with another rather than a measurement.

![The Estimates section on Black Friday: Shoppers' requests take about 39 ms, and 95% are done within about 78 ms, with none of their traffic failing, and running costs of about $1.18 an hour, $861 a month at that rate and $28.32 for the whole scenario.](https://docs.flozu.app/_astro/estimates-light.DanP7pIY_SrCuU.webp)

## What the estimates say

**Estimates**, under **Time and cost** in **What happens**, lists each part where traffic starts, such as your shoppers, with:

- **How long requests take,** typically, and the time 95% of them are done within. It adds the slowest moment when that’s well past the rest, or when some requests time out.
- **How much of its traffic fails,** across the scenario and at its worst. That’s everything a failure breaks, what a limit or a full buffer turns away, and what waits so long it times out.

Then **Running costs**, once a part has a cost: what the map costs an hour on average, a month at that rate, and for the whole scenario, and an hour at its dearest moment. Select it to see the parts that cost something, at that moment.

Hover over a part’s health strip on the canvas to see roughly how long it takes at the playhead, such as “about 140 ms each”.

## Give a part its time and cost

Select a part and open its **Traffic** tab:

| Field | What it sets                                                                                                                                      |
| ----- | ------------------------------------------------------------------------------------------------------------------------------------------------- |
| Takes | How long it takes to handle one request while it has room, in milliseconds. Left empty, it takes a typical time for its kind, shown in the field. |
| Costs | What it costs to run for an hour, in dollars. For a part that auto-scales, what one copy costs, and a scenario adds up the copies it runs.        |

A queue or topic only holds work, so it has a cost but no time. People and apps where traffic starts have neither.

> **Tip**
>
> You don’t need a cost on every part. Give one to the parts whose cost changes with your design, such as the ones that auto-scale, and compare the totals.

### Typical times

A part with no time of its own takes the typical time for its kind:

| Part           | Takes  | A new copy starts in |
| -------------- | ------ | -------------------- |
| DNS            | 20 ms  | None                 |
| CDN            | 20 ms  | None                 |
| Firewall       | 2 ms   | 60 s                 |
| Gateway        | 5 ms   | 60 s                 |
| Sign-in        | 100 ms | 2 min                |
| Load balancer  | 1 ms   | 60 s                 |
| Rate limiter   | 1 ms   | 30 s                 |
| Service        | 50 ms  | 90 s                 |
| Worker         | 500 ms | 90 s                 |
| Function       | 100 ms | 2 s                  |
| Scheduler      | None   | 60 s                 |
| AI model       | 2 s    | 5 min                |
| Queue          | 5 ms   | 2 min                |
| Topic          | 5 ms   | 2 min                |
| Database       | 10 ms  | 10 min               |
| Cache          | 1 ms   | 5 min                |
| Search         | 50 ms  | 10 min               |
| Storage        | 50 ms  | 60 s                 |
| Data warehouse | 2 s    | 2 min                |
| Endpoint       | 50 ms  | 90 s                 |
| Module         | 10 ms  | 90 s                 |
| Code file      | 5 ms   | 90 s                 |
| Table          | 5 ms   | 10 min               |
| Custom part    | 50 ms  | 2 min                |

## See what a fix costs

Fixes come with what they cost, where the parts have one:

- **Time and cost** advice says what keeping more copies warm costs a month, or what letting a part scale in saves.
- On the [Compare screen](https://docs.flozu.app/guides/versions-and-proposals.md#replay-a-scenario), the verdict adds the change in cost, such as “After, nobody notices, for about $310 a month more”. Below it, **Requests take, typically** shows where requests got faster or slower, where none of them fail on either map, and **Running costs** what each map costs a month at that rate.