[Feature]: Filter spans before exporting (Datadog)

[fw42]

Hello,

I'm using opentelemetry-datadog and I'm missing a feature that I think might be useful to add.

I've tried implementing my own sampling algorithm but been running into limitations with with_sampler. For example, I'd like to access attributes of the root span when making a sampling decision in a non-root span (for example, root span contains a "user_id", and I want to sample following spans only for specific users). Another example is using random sampling, but if the request turned out to be an error (which might only be known a couple of spans later), then I want to overwrite those sampling decisions (i.e., if the request is an error, then always include all spans).

What component are you working with?

opentelemetry-datadog

Describe the solution you'd like:

It looks like other Datadog tracing libraries do have this feature.

Something that would help me implement this is the ability to define a custom "filter function" that runs after all spans have been collected but before they are being exported to Datadog.

Any thoughts on this?

Thanks!