[DOC] TraceQL: documentation to filter traces where a span attribute exists

[cyrille-leclerc]

Is your feature request related to a problem? Please describe.

When troubleshooting my application, I would like to search for traces having a specific attribute being defined.
For example, for the operation getProduct, I want to find traces containing SQL spans, traces that contain a span with an attribute db.type.

I want to write this query without having to know what are the possible values for db.type, just saying that the attribute db.type is defined.

When using ElasticSearch & Kibana, it's the syntax my_field: * where * means "exist in any form".
I would like the TraceQL docs to document how I can do the equivalent with Tempo.

cc @knylander-grafana

[faustodavid]

Hi @cyrille-leclerc, you can specify in your TraceQL that an attribute need to have value.

The following query will return all spans that have the attribute db.type defined:

{span.db.type!=""}

[joe-elliott]

This is a great tip but not entirely true. This will return any spans that have a string attribute named span.db.type that has a value besides "".

{span.db.type!=""}

Due to the way we assert types there is no way to see if an attribute of any type exists. We have an issue here:

#2188

I favor

{ span.db.type != nil }

but others have expressed they like:

{ exists(span.db.type) }

[faustodavid]

Indeed, { span.db.type != nil } looks more intuitive.

[knylander-grafana]

@joe-elliott From what you said above, it sounds like the solution to be able to complete what Cyrille wants to do depends upon #2188. I'll add a note to your issue in progress that #2465 creates documentation for #2188. I can use Cyrille's question in the description as an example in the documentation.

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