Clarify default sampler

[seemk]

OpenTelemetry defaults to parentbased_always_on, but this is not consistent across our distributions:

• parentbased_always_on is used by Node.js, .NET, Python
• always_on is used by Java, Go

If we are advertising as a no sampling solution, we should default to always_on, but still allow for customers to change it.
Using parentbased_always_on can cause data loss if customers have previously set up cloud tracing, which injects a traceparent with 00 for traceflags.

[seemk]

@akubik-splunk

[pellared]

Wouldn't changing the default be a breaking change for a distribution?

I see it as a breaking change from semantic point of view. If we change the default in Node.js, .NET, Python distributions then I would advise to bump the major version.

[akubik-splunk]

In which distros this is marked as stable?
If this is marked as stable we must consider releasing this as braking change and bump the major release
As option we can consider aligning the Node.js and making it braking change only there
This is another reason we need compatibility matrix

[pellared]

In which distros this is marked as stable?

For sure in .NET it is stable.

In Python it is part of its SDK which is stable.

[akubik-splunk]

In which distros this is marked as stable?

For sure in .NET it is stable.

In Python it is part of its SDK which is stable.

So it seems to me that we should prep for the major bump and if possible bundle it up with other changes e.g. HTTP semantics :) for .NET and for Python as well. If there are other major changes that we would like to do let's use this as opportunity to do so. We would target such changes for the Jan-Feb next year though