Fix priority sampling activation #868
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| @@ -69,7 +69,7 @@ class RateByServiceSampler < Sampler | |||
| DEFAULT_KEY = 'service:,env:'.freeze | |||
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| def initialize(rate = 1.0, opts = {}) | |||
| @env = opts.fetch(:env, Datadog.tracer.tags[:env]) | |||
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This class had a reference to the global tracer which was causing a circular reference and failure to load when priority sampling was enabled by default. This component should not know about the tracer or any global settings, it should be given proper configuration.
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I had the same issue while doing sampling work.
I like this solution 👍
| @@ -173,7 +173,7 @@ | |||
| headers = datum[:headers] | |||
| expect(headers).to include(Datadog::Ext::DistributedTracing::HTTP_HEADER_TRACE_ID => span.trace_id.to_s) | |||
| expect(headers).to include(Datadog::Ext::DistributedTracing::HTTP_HEADER_PARENT_ID => span.span_id.to_s) | |||
| expect(headers).to_not include(Datadog::Ext::DistributedTracing::HTTP_HEADER_SAMPLING_PRIORITY) | |||
| expect(headers).to include(Datadog::Ext::DistributedTracing::HTTP_HEADER_SAMPLING_PRIORITY) | |||
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Evidently our integration tests were expecting sampling priority to be off by default as well...
| @@ -25,6 +25,7 @@ | |||
| it { expect(trace).to eq(result) } | |||
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| it 'tracks the number of allocations made in the span' do | |||
| skip 'Test unstable; improve stability before re-enabling.' | |||
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This has been a super flaky test that has been breaking builds; disabled it for now.
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does it now break builds because of this PR, or has it always been flaky?
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It's always been flaky. It just was breaking the build too many times now when I was trying to fix things.
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please put into a separate PR
lib/ddtrace/tracer.rb
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| @@ -441,7 +444,8 @@ def activate_priority_sampling!(base_sampler = nil) | |||
| @sampler = if base_sampler.is_a?(PrioritySampler) | |||
| base_sampler | |||
| else | |||
| PrioritySampler.new(base_sampler: base_sampler) | |||
| PrioritySampler.new(base_sampler: base_sampler, | |||
| post_sampler: Datadog::RateByServiceSampler.new(1.0, env: tags[:env])) | |||
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why is this change needed?
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Because of https://github.com/DataDog/dd-trace-rb/pull/868/files#diff-075cdbe46a2ed147b75f5da176ae2e88L72
This is how you ensure env is still properly applied from the tracer to the sampler.
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what happens if the env tag is changed after we initialize a priority sampler?
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It won't be read; same as it is today.The only difference is maybe you were configuring tags at the same time you activated priority sampling manually, so maybe it would've applied, maybe it wouldn't; depends on the order the settings were applied.
Only conceivable way is to change the value to a lazy Proc. You could argue that the key_for(span) function should be this Proc, and when you define a RateByServiceSampler, you should provide this proc that acts as means of resolving a key. Which would make this more of a RateByKeySampler which can optionally configured to use an env or not, which I think would be a better design.
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Okay, I did a small refactor of the RateByServiceSampler and changed it to resolve the env from a Proc. Feel free to take a look.
| @@ -25,6 +25,7 @@ | |||
| it { expect(trace).to eq(result) } | |||
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| it 'tracks the number of allocations made in the span' do | |||
| skip 'Test unstable; improve stability before re-enabling.' | |||
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does it now break builds because of this PR, or has it always been flaky?
The tracer should enable priority sampling by default, but it does not; instead it's only activating priority sampling when
Tracer#configurewas called.This pull request ensures that priority sampling is enabled by default.