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Remove warnings about Span.UpdateName #754

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Aug 3, 2020
Merged

Remove warnings about Span.UpdateName #754

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e48fd21
Remove warnings about Span.UpdateName
iNikem Jul 31, 2020
fd86afa
Better wording about samplers decisions
iNikem Jul 31, 2020
9de2721
Better wording about samplers decisions
iNikem Jul 31, 2020
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17 changes: 8 additions & 9 deletions specification/trace/api.md
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Expand Up @@ -415,6 +415,11 @@ clearing the previous value and dropping the attribute key from the set of attri
Note that the OpenTelemetry project documents certain ["standard
attributes"](semantic_conventions/README.md) that have prescribed semantic meanings.

Note that [samplers](sdk.md#sampler) can only consider information already
present during span creation. Any changes done later, including new or changed
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I don't think this is accurate, especially given open-telemetry/oteps#115

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This reflects current state of the spec:

Sampler interface allows users to create custom samplers which will return a sampling SamplingResult based on information that is typically available just before the Span was created.

I cannot propose a PR to spec based on not yet merged OTEP, can I?

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Then why remove the warning? Until that OTEP is implemented, samplers cannot react to changes in the span name, can they?

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That was discussed at length in #506 . Span.updateName has legit use-cases and having this warning confuses people: "why have a method but discourage to use it?" We cannot remove the method, thus I propose to remove the warning.

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For me, the discussion in OTEP 115 clarifies that there are two distinct kinds of sampling decision. There is a head sampling decision that is irrevocable, made when the span starts, but this is only a provisional decision to begin gathering a span. There is still a tail sampling decision to be made that can incorporate new information, and we shouldn't mix terms and call these both a sampling decision.

This conversation appears to relate to the first decision, which practically by definition can't be changed because it's history by the time any new information arrives. I would just be clear that when we say "Sampler" (capital "S") we are referring to an initial decision that can't be revoked, not a final decision.

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I agree with that. And link here to "samplers" as defined in SDK spec. I can change "sampler" to "Samplers" if that will make it clearer :)

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Also, @yurishkuro , I would like to point your attention that this PR solves issue #468 which is triaged for GA and assigned P1. If you disagree with this, that issue would be a better place to try and change this decision.

attributes, cannot change their decisions.


#### Add Events

A `Span` MUST have the ability to add events. Events have a time associated
Expand Down Expand Up @@ -464,15 +469,9 @@ The Span interface MUST provide:
Updates the `Span` name. Upon this update, any sampling behavior based on `Span`
name will depend on the implementation.

It is highly discouraged to update the name of a `Span` after its creation.
`Span` name is often used to group, filter and identify the logical groups of
spans. And often, filtering logic will be implemented before the `Span` creation
for performance reasons. Thus the name update may interfere with this logic.

The function name is called `UpdateName` to differentiate this function from the
regular property setter. It emphasizes that this operation signifies a major
change for a `Span` and may lead to re-calculation of sampling or filtering
decisions made previously depending on the implementation.
Note that [samplers](sdk.md#sampler) can only consider information already
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present during span creation. Any changes done later, including updated span
name, cannot change their decisions.

Alternatives for the name update may be late `Span` creation, when Span is
started with the explicit timestamp from the past at the moment where the final
Expand Down