---
title: "Estimate cardinality from traces | Grafana Tempo documentation"
description: "Estimate cardinality from traces to understand the impact of service graphs."
---

# Estimate cardinality from traces

Cardinality can pose a problem when you have lots of services. There isn’t a direct formula or solution to this issue. The following guide should help estimate the cardinality that a feature generates.

For more information on cardinality, refer to the [Cardinality](../cardinality/) documentation.

### How to estimate the cardinality

The amount of edges depends on the number of nodes in the system and the direction of the requests between them. Let’s call this amount hops. Every hop is a unique combination of client + server labels.

For example:

- A system with 3 nodes `(A, B, C)` of which `A` only calls `B` and `B` only calls `C` will have 2 hops `(A → B, B → C)`
- A system with 3 nodes `(A, B, C)` that call each other (that is, all bidirectional links) will have 6 hops `(A → B, B → A, B → C, C → B, A → C, C → A)`

You can’t calculate the amount of hops automatically based upon the nodes, but it should be a value between `#services - 1` and `#services!`.

If you know the amount of hops in a system, you can calculate the cardinality of the generated service graphs (assuming `#hb` is the number of histogram buckets):

![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```none
  traces_service_graph_request_total: #hops
  traces_service_graph_request_failed_total: #hops
  traces_service_graph_request_server_seconds: #hb * #hops
  traces_service_graph_request_client_seconds: #hb * #hops
  traces_service_graph_unpaired_spans_total: #services (absolute worst case)
  traces_service_graph_dropped_spans_total: #services (absolute worst case)
```

Finally, you get the following cardinality estimation:

![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```none
  Sum: [([2 * #hb] + 2) * #hops] + [2 * #services]
```

> Note
> 
> If `enable_messaging_system_latency_histogram` configuration is set to `true`, another histogram is produced:
> 
> ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy
> 
> ```none
>   traces_service_graph_request_messaging_system_seconds: #hb * #hops
> ```
> 
> In that case, the estimation formula would be:
> 
> ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy
> 
> ```none
>   Sum: [([3 * #hb] + 2) * #hops] + [2 * #services]
> ```

> Note
> 
> To estimate the number of metrics, refer to the [Dry run metrics generator](../cardinality/) documentation.