API to retrieve trace spans in bulk for multiple trace ids

[nielsreijers]

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

We're building a system to analyse failures, where we need to take a samples of sufficient size from failed and successful requests to find the common causes for requests to fail.

As input we have a set of trace ids, which we currently retrieve one by one through the GET /api/traces/<traceID> endpoint.

This takes some time, even with start and end parameters set. In our setup, older traces already moved to the back end storage take anywhere from 400 to 1000ms.

Since all traces are in the same time window, an endpoint that would allow us to get multiple traces at once could probably be much more efficient.

Describe the solution you'd like
An endpoint that accepts a list of trace ids instead of a single trace id and returns all found traces in one response.

Describe alternatives you've considered
We're currently retrieving them in parallel, but this doesn't seem to scale beyond a speedup of around 4-5x.

Additional context