Support for Sampling in OpenTelemetry Logger

[gunzip]

Hi, I see that it's possible to add a Sampler to a Tracer, but I couldn't find a way to apply a sampler to a Logger.

Is there currently any way to apply sampling settings to logs (e.g., console.log)? If not, are there any plans to introduce log sampling in OpenTelemetry JS?

Use case: In high-throughput applications, being able to control the volume of logs generated would be useful to avoid excessive log noise and reduce costs.

Thanks in advance!

[pichlermarc]

Hi @gunzip, thanks for reaching out.

We aim to implement https://github.com/open-telemetry/opentelemetry-specification/ with our Logs SDK, and there's no concept for Sampling on the client side this at the moment. We are not planning to add such a feature unless there's an effort in the specification to do this for all language implementations.

This is mostly to avoid:

• conflicts with future specification versions
• diverging in core feature-sets between language implementations

You may be able to request a feature over at the spec to get the ball rolling there, we will then eventually implement the feature here.

Some ideas for workarounds:

If you're tracing with OTel in the same app, then a LogRecord can have a spanContext which includes traceFlags, which can be used to determine if the linked trace has been sampled. You could then drop it using a co-deployed OpenTelemetry Collector. That's just a workaround though and still wastes some resources as the logs need to be serialized in the app and de-serialized on the collector.

One way to work around that would be to implement a custom LogRecordProcessor. This processor could accept another LogRecordProcessor in the constructor, and would onEmit() only forward LogRecords where the traceFlags indicate that the assoicated trace has been sampled.