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https://issues.apache.org/jira/browse/HTRACE-215?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14630744#comment-14630744
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Colin Patrick McCabe commented on HTRACE-215:
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I've been thinking about this, and I don't think the {{Sampler<T>}} type
provides any advantage over just plain old {{Sampler}}. It seems like in
practice pretty much every traced application and library uses the
{{SamplerFactory}}, which just returns a {{Sampler<?>}}. We don't have a
single example of a {{Sampler}} which is anything other than
{{Sampler<Object>}}, or a single example of one that uses the templated
parameter.
The fundamental issue is that if you want to use a {{Sampler<Foo>}}, you have
to change your code to call {{startSpan("spanName", mySampler, myFoo)}}. If
we're going to start hacking up the application code, we could easily do
something like this:
{code}
startSpan("spanName", myFoo.saysItIsOk() ? AlwaysSampler.INSTANCE :
NeverSampler.INSTANCE)
{code}
If this seems to cumbersome, we could always write a utility function wrapping
it, similar to {{DFSClient#getPathTraceScope}}, which creates a new span with a
"path" KV annotation.
So in summary, the generic type parameter seems to add no additional value, and
it leads to a lot of ugly {{<?>}} boilerplate and findbugs warnings. Let's zap
it in 4.0.
> Simplify the Sampler type
> -------------------------
>
> Key: HTRACE-215
> URL: https://issues.apache.org/jira/browse/HTRACE-215
> Project: HTrace
> Issue Type: Sub-task
> Affects Versions: 4.0
> Reporter: Colin Patrick McCabe
> Assignee: Colin Patrick McCabe
>
> The Sampler type currently is parameterized on another type, like
> {{Sampler<T>}}. However, this is not really useful now that we have moved to
> a model of creating samplers from the {{SamplerFactory}}, since the
> {{SamplerFactory}} returns a {{Sampler<?>}}.
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