diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4ac4180a5c4..3c3b96784f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,21 @@
 
 ## [Unreleased (beta)]
 
+## [0.19.0] - 2019-01-22
+
+Release notes: https://github.com/DataDog/dd-trace-rb/releases/tag/v0.19.0
+
+Git diff: https://github.com/DataDog/dd-trace-rb/compare/v0.18.3...v0.19.0
+
+### Added
+
+ - Tracer#active_correlation for adding correlation IDs to logs. (#660, #664, #673)
+ - Opt-in support for `event_sample_rate` tag for some integrations. (#665, #666)
+
+### Changed
+
+ - Priority sampling enabled by default. (#654)
+
 ## [0.18.3] - 2019-01-17
 
 Release notes: https://github.com/DataDog/dd-trace-rb/releases/tag/v0.18.3
@@ -627,8 +642,9 @@ Release notes: https://github.com/DataDog/dd-trace-rb/releases/tag/v0.3.1
 
 Git diff: https://github.com/DataDog/dd-trace-rb/compare/v0.3.0...v0.3.1
 
-[Unreleased (stable)]: https://github.com/DataDog/dd-trace-rb/compare/v0.18.3...master
-[Unreleased (beta)]: https://github.com/DataDog/dd-trace-rb/compare/v0.18.3...0.19-dev
+[Unreleased (stable)]: https://github.com/DataDog/dd-trace-rb/compare/v0.19.0...master
+[Unreleased (beta)]: https://github.com/DataDog/dd-trace-rb/compare/v0.19.0...0.20-dev
+[0.19.0]: https://github.com/DataDog/dd-trace-rb/compare/v0.18.3...v0.19.0
 [0.18.3]: https://github.com/DataDog/dd-trace-rb/compare/v0.18.2...v0.18.3
 [0.18.2]: https://github.com/DataDog/dd-trace-rb/compare/v0.18.1...v0.18.2
 [0.18.1]: https://github.com/DataDog/dd-trace-rb/compare/v0.18.0...v0.18.1
diff --git a/Rakefile b/Rakefile
index 344c9fc9c95..676f354c1bb 100644
--- a/Rakefile
+++ b/Rakefile
@@ -46,7 +46,7 @@ namespace :spec do
   end
 
   RSpec::Core::RakeTask.new(:contrib) do |t|
-    t.pattern = 'spec/**/contrib/{configurable,integration,patchable,patcher,registerable,configuration/*}_spec.rb'
+    t.pattern = 'spec/**/contrib/{configurable,integration,patchable,patcher,registerable,sampling,configuration/*}_spec.rb'
   end
 
   [
diff --git a/docs/GettingStarted.md b/docs/GettingStarted.md
index a076565664b..940ce69a81e 100644
--- a/docs/GettingStarted.md
+++ b/docs/GettingStarted.md
@@ -62,6 +62,7 @@ For descriptions of terminology used in APM, take a look at the [official docume
      - [Processing pipeline](#processing-pipeline)
          - [Filtering](#filtering)
          - [Processing](#processing)
+     - [Trace correlation](#trace-correlation)
      - [OpenTracing](#opentracing)
 
 ## Compatibility
@@ -517,6 +518,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 
 | Key | Description | Default |
 | --- | ----------- | ------- |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `service_name` | Service name used for `DelayedJob` instrumentation | `'delayed_job'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
 
@@ -865,6 +867,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 
 | Key | Description | Default |
 | --- | ----------- | ------- |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `service_name` | Service name used for `racecar` instrumentation | `'racecar'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
 
@@ -897,6 +900,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | --- | ----------- | ------- |
 | `application` | Your Rack application. Required for `middleware_names`. | `nil` |
 | `distributed_tracing` | Enables [distributed tracing](#distributed-tracing) so that this service trace is connected with a trace of another service if tracing headers are received | `false` |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `headers` | Hash of HTTP request or response headers to add as tags to the `rack.request`. Accepts `request` and `response` keys with Array values e.g. `['Last-Modified']`. Adds `http.request.headers.*` and `http.response.headers.*` tags respectively. | `{ response: ['Content-Type', 'X-Request-ID'] }` |
 | `middleware_names` | Enable this if you want to use the middleware classes as the resource names for `rack` spans. Requires `application` option to use. | `false` |
 | `quantize` | Hash containing options for quantization. May include `:query` or `:fragment`. | `{}` |
@@ -1006,6 +1010,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | Key | Description | Default |
 | --- | ----------- | ------- |
 | `enabled` | Defines whether Rake tasks should be traced. Useful for temporarily disabling tracing. `true` or `false` | `true` |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `quantize` | Hash containing options for quantization of task arguments. See below for more details and examples. | `{}` |
 | `service_name` | Service name used for `rake` instrumentation | `'rake'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
@@ -1107,6 +1112,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 
 | Key | Description | Default |
 | --- | ----------- | ------- |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `service_name` | Service name used for `resque` instrumentation | `'resque'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
 | `workers` | An array including all worker classes you want to trace (eg `[MyJob]`) | `[]` |
@@ -1198,6 +1204,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 
 | Key | Description | Default |
 | --- | ----------- | ------- |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `service_name` | Service name used for `shoryuken` instrumentation | `'shoryuken'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
 
@@ -1220,6 +1227,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | Key | Description | Default |
 | --- | ----------- | ------- |
 | `client_service_name` | Service name used for client-side `sidekiq` instrumentation | `'sidekiq-client'` |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `service_name` | Service name used for server-side `sidekiq` instrumentation | `'sidekiq'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
 
@@ -1271,6 +1279,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 
 | Key | Description | Default |
 | --- | ----------- | ------- |
+| `event_sample_rate` | Rate which spans should be sampled for search and analytics. | `nil` |
 | `service_name` | Service name used for `sucker_punch` instrumentation | `'sucker_punch'` |
 | `tracer` | `Datadog::Tracer` used to perform instrumentation. Usually you don't need to set this. | `Datadog.tracer` |
 
@@ -1356,15 +1365,7 @@ The sampler can set the priority to the following values:
  - `Datadog::Ext::Priority::AUTO_REJECT`: the sampler automatically decided to reject the trace.
  - `Datadog::Ext::Priority::AUTO_KEEP`: the sampler automatically decided to keep the trace.
 
-For now, priority sampling is disabled by default. Enabling it ensures that your sampled distributed traces will be complete. To enable the priority sampling:
-
-```ruby
-Datadog.configure do |c|
-  c.tracer priority_sampling: true
-end
-```
-
-Once enabled, the sampler will automatically assign a priority of 0 or 1 to traces, depending on their service and volume.
+Priority sampling is enabled by default. Enabling it ensures that your sampled distributed traces will be complete. Once enabled, the sampler will automatically assign a priority of 0 or 1 to traces, depending on their service and volume.
 
 You can also set this priority manually to either drop a non-interesting trace or to keep an important one. For that, set the `context#sampling_priority` to:
 
@@ -1613,6 +1614,77 @@ Datadog::Pipeline.before_flush(
 )
 ```
 
+### Trace correlation
+
+In many cases, such as logging, it may be useful to correlate trace IDs to other events or data streams, for easier cross referencing. The tracer can produce a correlation identifier for the currently active trace via `active_correlation`, which can be used to decorate these other data sources.
+
+```ruby
+# When a trace is active...
+Datadog.tracer.trace('correlation.example') do
+  # Returns #<Datadog::Correlation::Identifier>
+  correlation = Datadog.tracer.active_correlation
+  correlation.trace_id # => 5963550561812073440
+  correlation.span_id # => 2232727802607726424
+end
+
+# When a trace isn't active...
+correlation = Datadog.tracer.active_correlation
+# Returns #<Datadog::Correlation::Identifier>
+correlation = Datadog.tracer.active_correlation
+correlation.trace_id # => 0
+correlation.span_id # => 0
+```
+
+#### For logging in Ruby applications
+
+To add correlation IDs to your logger, add a log formatter which retrieves the correlation IDs with `Datadog.tracer.active_correlation`, then add them to the message.
+
+To properly correlate with Datadog logging, be sure the following is present:
+
+ - `dd.trace_id=<TRACE_ID>`: Where `<TRACE_ID>` is equal to `Datadog.tracer.active_correlation.trace_id` or `0` if no trace is active.
+ - `dd.span_id=<SPAN_ID>`: Where `<SPAN_ID>` is equal to `Datadog.tracer.active_correlation.span_id` or `0` if no trace is active.
+
+By default, `Datadog::Correlation::Identifier#to_s` will return `dd.trace_id=<TRACE_ID> dd.span_id=<SPAN_ID>`.
+
+An example of this in practice:
+
+```ruby
+require 'ddtrace'
+require 'logger'
+
+logger = Logger.new(STDOUT)
+logger.progname = 'my_app'
+logger.formatter  = proc do |severity, datetime, progname, msg|
+  "[#{datetime}][#{progname}][#{severity}][#{Datadog.tracer.active_correlation}] #{msg}\n"
+end
+
+# When no trace is active
+logger.warn('This is an untraced operation.')
+# [2019-01-16 18:38:41 +0000][my_app][WARN][dd.trace_id=0 dd.span_id=0] This is an untraced operation.
+
+# When a trace is active
+Datadog.tracer.trace('my.operation') { logger.warn('This is a traced operation.') }
+# [2019-01-16 18:38:41 +0000][my_app][WARN][dd.trace_id=8545847825299552251 dd.span_id=3711755234730770098] This is a traced operation.
+```
+
+#### For logging in Rails applications
+
+Rails applications which are configured with a `ActiveSupport::TaggedLogging` logger can append correlation IDs as tags to log output. The default Rails logger implements this tagged logging, making it easier to add correlation tags.
+
+In your Rails environment configuration file, add the following:
+
+```ruby
+Rails.application.configure do
+  config.log_tags = [proc { Datadog.tracer.active_correlation.to_s }]
+end
+
+# Web requests will produce:
+# [dd.trace_id=7110975754844687674 dd.span_id=7518426836986654206] Started GET "/articles" for 172.22.0.1 at 2019-01-16 18:50:57 +0000
+# [dd.trace_id=7110975754844687674 dd.span_id=7518426836986654206] Processing by ArticlesController#index as */*
+# [dd.trace_id=7110975754844687674 dd.span_id=7518426836986654206]   Article Load (0.5ms)  SELECT "articles".* FROM "articles"
+# [dd.trace_id=7110975754844687674 dd.span_id=7518426836986654206] Completed 200 OK in 7ms (Views: 5.5ms | ActiveRecord: 0.5ms)
+```
+
 ### OpenTracing
 
 For setting up Datadog with OpenTracing, see out [Quickstart for OpenTracing](#quickstart-for-opentracing) section for details.
diff --git a/lib/ddtrace/contrib/configuration/settings.rb b/lib/ddtrace/contrib/configuration/settings.rb
index c0973e5dc82..d830c7dd0c3 100644
--- a/lib/ddtrace/contrib/configuration/settings.rb
+++ b/lib/ddtrace/contrib/configuration/settings.rb
@@ -9,6 +9,7 @@ class Settings
 
         option :service_name
         option :tracer, default: Datadog.tracer
+        option :event_sample_rate
 
         def initialize(options = {})
           configure(options)
diff --git a/lib/ddtrace/contrib/delayed_job/plugin.rb b/lib/ddtrace/contrib/delayed_job/plugin.rb
index bef91e6f7b6..fdcbc8211de 100644
--- a/lib/ddtrace/contrib/delayed_job/plugin.rb
+++ b/lib/ddtrace/contrib/delayed_job/plugin.rb
@@ -1,4 +1,5 @@
 require 'delayed/plugin'
+require 'ddtrace/contrib/sampling'
 require 'ddtrace/contrib/delayed_job/ext'
 
 module Datadog
@@ -18,6 +19,7 @@ def self.instrument(job, &block)
                      end
 
           tracer.trace(Ext::SPAN_JOB, service: configuration[:service_name], resource: job_name) do |span|
+            Contrib::Sampling.set_event_sample_rate(span, configuration[:event_sample_rate])
             span.set_tag(Ext::TAG_ID, job.id)
             span.set_tag(Ext::TAG_QUEUE, job.queue) if job.queue
             span.set_tag(Ext::TAG_PRIORITY, job.priority)
diff --git a/lib/ddtrace/contrib/racecar/event.rb b/lib/ddtrace/contrib/racecar/event.rb
index 35d8bd4cf67..8110353ed0f 100644
--- a/lib/ddtrace/contrib/racecar/event.rb
+++ b/lib/ddtrace/contrib/racecar/event.rb
@@ -1,3 +1,4 @@
+require 'ddtrace/contrib/sampling'
 require 'ddtrace/contrib/active_support/notifications/event'
 require 'ddtrace/contrib/racecar/ext'
 
@@ -36,6 +37,7 @@ def process(span, event, _id, payload)
             span.service = configuration[:service_name]
             span.resource = payload[:consumer_class]
 
+            Contrib::Sampling.set_event_sample_rate(span, configuration[:event_sample_rate])
             span.set_tag(Ext::TAG_TOPIC, payload[:topic])
             span.set_tag(Ext::TAG_CONSUMER, payload[:consumer_class])
             span.set_tag(Ext::TAG_PARTITION, payload[:partition])
diff --git a/lib/ddtrace/contrib/rack/middlewares.rb b/lib/ddtrace/contrib/rack/middlewares.rb
index fe7e6d3fbc0..1092f81b1ac 100644
--- a/lib/ddtrace/contrib/rack/middlewares.rb
+++ b/lib/ddtrace/contrib/rack/middlewares.rb
@@ -1,6 +1,7 @@
 require 'ddtrace/ext/app_types'
 require 'ddtrace/ext/http'
 require 'ddtrace/propagation/http_propagator'
+require 'ddtrace/contrib/sampling'
 require 'ddtrace/contrib/rack/ext'
 require 'ddtrace/contrib/rack/request_queue'
 
@@ -25,7 +26,7 @@ def initialize(app)
         end
 
         def compute_queue_time(env, tracer)
-          return unless Datadog.configuration[:rack][:request_queuing]
+          return unless configuration[:request_queuing]
 
           # parse the request queue time
           request_start = Datadog::Contrib::Rack::QueueTime.get_request_start(env)
@@ -34,25 +35,25 @@ def compute_queue_time(env, tracer)
           tracer.trace(
             Ext::SPAN_HTTP_SERVER_QUEUE,
             start_time: request_start,
-            service: Datadog.configuration[:rack][:web_service_name]
+            service: configuration[:web_service_name]
           )
         end
 
         def call(env)
           # retrieve integration settings
-          tracer = Datadog.configuration[:rack][:tracer]
+          tracer = configuration[:tracer]
 
           # [experimental] create a root Span to keep track of frontend web servers
           # (i.e. Apache, nginx) if the header is properly set
           frontend_span = compute_queue_time(env, tracer)
 
           trace_options = {
-            service: Datadog.configuration[:rack][:service_name],
+            service: configuration[:service_name],
             resource: nil,
             span_type: Datadog::Ext::HTTP::TYPE
           }
 
-          if Datadog.configuration[:rack][:distributed_tracing]
+          if configuration[:distributed_tracing]
             context = HTTPPropagator.extract(env)
             tracer.provider.context = context if context.trace_id
           end
@@ -114,7 +115,7 @@ def call(env)
         end
 
         def resource_name_for(env, status)
-          if Datadog.configuration[:rack][:middleware_names] && env['RESPONSE_MIDDLEWARE']
+          if configuration[:middleware_names] && env['RESPONSE_MIDDLEWARE']
             "#{env['RESPONSE_MIDDLEWARE']}##{env['REQUEST_METHOD']}"
           else
             "#{env['REQUEST_METHOD']} #{status}".strip
@@ -138,13 +139,19 @@ def set_request_tags!(request_span, env, status, headers, response, original_env
           response_headers = parse_response_headers(headers || {})
 
           request_span.resource ||= resource_name_for(env, status)
+
+          # Set event sample rate, if available.
+          Contrib::Sampling.set_event_sample_rate(request_span, configuration[:event_sample_rate])
+
           if request_span.get_tag(Datadog::Ext::HTTP::METHOD).nil?
             request_span.set_tag(Datadog::Ext::HTTP::METHOD, env['REQUEST_METHOD'])
           end
+
           if request_span.get_tag(Datadog::Ext::HTTP::URL).nil?
-            options = Datadog.configuration[:rack][:quantize]
+            options = configuration[:quantize]
             request_span.set_tag(Datadog::Ext::HTTP::URL, Datadog::Quantization::HTTP.url(url, options))
           end
+
           if request_span.get_tag(Datadog::Ext::HTTP::BASE_URL).nil?
             request_obj = ::Rack::Request.new(env)
 
@@ -157,6 +164,7 @@ def set_request_tags!(request_span, env, status, headers, response, original_env
 
             request_span.set_tag(Datadog::Ext::HTTP::BASE_URL, base_url)
           end
+
           if request_span.get_tag(Datadog::Ext::HTTP::STATUS_CODE).nil? && status
             request_span.set_tag(Datadog::Ext::HTTP::STATUS_CODE, status)
           end
@@ -186,6 +194,10 @@ def set_request_tags!(request_span, env, status, headers, response, original_env
           If you need the Rack request span, try using `Datadog.tracer.active_span`.
           This key will be removed in version 1.0).freeze
 
+        def configuration
+          Datadog.configuration[:rack]
+        end
+
         def add_deprecation_warnings(env)
           env.instance_eval do
             unless instance_variable_defined?(:@patched_with_datadog_warnings)
@@ -225,7 +237,7 @@ def without_datadog_warnings
 
         def parse_request_headers(env)
           {}.tap do |result|
-            whitelist = Datadog.configuration[:rack][:headers][:request] || []
+            whitelist = configuration[:headers][:request] || []
             whitelist.each do |header|
               rack_header = header_to_rack_header(header)
               if env.key?(rack_header)
@@ -237,7 +249,7 @@ def parse_request_headers(env)
 
         def parse_response_headers(headers)
           {}.tap do |result|
-            whitelist = Datadog.configuration[:rack][:headers][:response] || []
+            whitelist = configuration[:headers][:response] || []
             whitelist.each do |header|
               if headers.key?(header)
                 result[Datadog::Ext::HTTP::ResponseHeaders.to_tag(header)] = headers[header]
diff --git a/lib/ddtrace/contrib/rake/instrumentation.rb b/lib/ddtrace/contrib/rake/instrumentation.rb
index d2d109baa1c..f1f81961f69 100644
--- a/lib/ddtrace/contrib/rake/instrumentation.rb
+++ b/lib/ddtrace/contrib/rake/instrumentation.rb
@@ -1,3 +1,4 @@
+require 'ddtrace/contrib/sampling'
 require 'ddtrace/contrib/rake/ext'
 
 module Datadog
@@ -41,6 +42,7 @@ def shutdown_tracer!
 
           def annotate_invoke!(span, args)
             span.resource = name
+            Contrib::Sampling.set_event_sample_rate(span, configuration[:event_sample_rate])
             span.set_tag(Ext::TAG_TASK_ARG_NAMES, arg_names)
             span.set_tag(Ext::TAG_INVOKE_ARGS, quantize_args(args)) unless args.nil?
           rescue StandardError => e
diff --git a/lib/ddtrace/contrib/resque/patcher.rb b/lib/ddtrace/contrib/resque/patcher.rb
index 3a0d8bb51c9..ebab2584d9f 100644
--- a/lib/ddtrace/contrib/resque/patcher.rb
+++ b/lib/ddtrace/contrib/resque/patcher.rb
@@ -19,7 +19,6 @@ def patch
           do_once(:resque) do
             begin
               require_relative 'resque_job'
-              add_pin
               get_option(:workers).each { |worker| worker.extend(ResqueJob) }
             rescue StandardError => e
               Datadog::Tracer.log.error("Unable to apply Resque integration: #{e}")
@@ -27,15 +26,6 @@ def patch
           end
         end
 
-        def add_pin
-          Pin.new(
-            get_option(:service_name),
-            app: Ext::APP,
-            app_type: Datadog::Ext::AppTypes::WORKER,
-            tracer: get_option(:tracer)
-          ).onto(::Resque)
-        end
-
         def get_option(option)
           Datadog.configuration[:resque].get_option(option)
         end
diff --git a/lib/ddtrace/contrib/resque/resque_job.rb b/lib/ddtrace/contrib/resque/resque_job.rb
index 6d05f36f399..f0d05bd70c6 100644
--- a/lib/ddtrace/contrib/resque/resque_job.rb
+++ b/lib/ddtrace/contrib/resque/resque_job.rb
@@ -1,5 +1,6 @@
 require 'ddtrace/ext/app_types'
 require 'ddtrace/sync_writer'
+require 'ddtrace/contrib/sampling'
 require 'ddtrace/contrib/sidekiq/ext'
 require 'resque'
 
@@ -9,13 +10,13 @@ module Resque
       # Uses Resque job hooks to create traces
       module ResqueJob
         def around_perform(*_)
-          pin = Pin.get_from(::Resque)
-          return yield unless pin && pin.tracer
-          pin.tracer.trace(Ext::SPAN_JOB, service: pin.service) do |span|
+          return yield unless datadog_configuration && tracer
+
+          tracer.trace(Ext::SPAN_JOB, span_options) do |span|
             span.resource = name
-            span.span_type = pin.app_type
+            span.span_type = Datadog::Ext::AppTypes::WORKER
+            Contrib::Sampling.set_event_sample_rate(span, datadog_configuration[:event_sample_rate])
             yield
-            span.service = pin.service
           end
         end
 
@@ -28,8 +29,27 @@ def on_failure_shutdown_tracer(*_)
         end
 
         def shutdown_tracer_when_forked!
-          pin = Datadog::Pin.get_from(Resque)
-          pin.tracer.shutdown! if pin && pin.tracer && pin.config && pin.config[:forked]
+          tracer.shutdown! if forked?
+        end
+
+        private
+
+        def forked?
+          pin = Datadog::Pin.get_from(::Resque)
+          return false unless pin
+          pin.config[:forked] == true
+        end
+
+        def span_options
+          { service: datadog_configuration[:service_name] }
+        end
+
+        def tracer
+          datadog_configuration.tracer
+        end
+
+        def datadog_configuration
+          Datadog.configuration[:resque]
         end
       end
     end
@@ -37,12 +57,17 @@ def shutdown_tracer_when_forked!
 end
 
 Resque.after_fork do
-  # get the current tracer
-  pin = Datadog::Pin.get_from(Resque)
-  next unless pin && pin.tracer
-  pin.config ||= {}
-  pin.config[:forked] = true
-
-  # clean the state so no CoW happens
-  pin.tracer.provider.context = nil
+  configuration = Datadog.configuration[:resque]
+  next if configuration.nil?
+
+  # Add a pin, marking the job as forked.
+  # Used to trigger shutdown in forks for performance reasons.
+  Datadog::Pin.new(
+    configuration[:service_name],
+    config: { forked: true }
+  ).onto(::Resque)
+
+  # Clean the state so no CoW happens
+  next if configuration[:tracer].nil?
+  configuration[:tracer].provider.context = nil
 end
diff --git a/lib/ddtrace/contrib/sampling.rb b/lib/ddtrace/contrib/sampling.rb
new file mode 100644
index 00000000000..e61ee55909d
--- /dev/null
+++ b/lib/ddtrace/contrib/sampling.rb
@@ -0,0 +1,14 @@
+require 'ddtrace/ext/priority'
+
+module Datadog
+  module Contrib
+    # Defines sampling behavior for integrations
+    module Sampling
+      module_function
+
+      def set_event_sample_rate(span, sample_rate)
+        span.set_metric(Datadog::Ext::Priority::TAG_EVENT_SAMPLE_RATE, sample_rate) unless sample_rate.nil?
+      end
+    end
+  end
+end
diff --git a/lib/ddtrace/contrib/shoryuken/tracer.rb b/lib/ddtrace/contrib/shoryuken/tracer.rb
index 71e6d6aa788..46386073fef 100644
--- a/lib/ddtrace/contrib/shoryuken/tracer.rb
+++ b/lib/ddtrace/contrib/shoryuken/tracer.rb
@@ -1,16 +1,19 @@
+require 'ddtrace/contrib/sampling'
+
 module Datadog
   module Contrib
     module Shoryuken
       # Tracer is a Shoryuken server-side middleware which traces executed jobs
       class Tracer
         def initialize(options = {})
-          @tracer = options[:tracer] || Datadog.configuration[:shoryuken][:tracer]
-          @shoryuken_service = options[:service_name] || Datadog.configuration[:shoryuken][:service_name]
+          @tracer = options[:tracer] || configuration[:tracer]
+          @shoryuken_service = options[:service_name] || configuration[:service_name]
           set_service_info(@shoryuken_service)
         end
 
         def call(worker_instance, queue, sqs_msg, body)
           @tracer.trace(Ext::SPAN_JOB, service: @shoryuken_service, span_type: Datadog::Ext::AppTypes::WORKER) do |span|
+            Contrib::Sampling.set_event_sample_rate(span, configuration[:event_sample_rate])
             span.resource = resource(worker_instance, body)
             span.set_tag(Ext::TAG_JOB_ID, sqs_msg.message_id)
             span.set_tag(Ext::TAG_JOB_QUEUE, queue)
@@ -31,8 +34,12 @@ def resource(worker_instance, body)
           job_class || worker_instance.class.name
         end
 
+        def configuration
+          Datadog.configuration[:shoryuken]
+        end
+
         def set_service_info(service)
-          return if @tracer.services[service]
+          return if @tracer.nil? || @tracer.services[service]
           @tracer.set_service_info(
             service,
             Ext::APP,
diff --git a/lib/ddtrace/contrib/sidekiq/client_tracer.rb b/lib/ddtrace/contrib/sidekiq/client_tracer.rb
index 0c6954abeda..0c9535ac6b4 100644
--- a/lib/ddtrace/contrib/sidekiq/client_tracer.rb
+++ b/lib/ddtrace/contrib/sidekiq/client_tracer.rb
@@ -1,4 +1,5 @@
 require 'ddtrace/contrib/sidekiq/tracing'
+require 'ddtrace/contrib/sampling'
 
 module Datadog
   module Contrib
@@ -9,19 +10,18 @@ class ClientTracer
 
         def initialize(options = {})
           super
-          @sidekiq_service = options[:client_service_name] || Datadog.configuration[:sidekiq][:client_service_name]
+          @sidekiq_service = options[:client_service_name] || configuration[:client_service_name]
+          set_service_info(@sidekiq_service)
         end
 
         # Client middleware arguments are documented here:
         #   https://github.com/mperham/sidekiq/wiki/Middleware#client-middleware
         def call(worker_class, job, queue, redis_pool)
-          service = @sidekiq_service
-          set_service_info(service)
-
           resource = job_resource(job)
 
-          @tracer.trace(Ext::SPAN_PUSH, service: service) do |span|
+          @tracer.trace(Ext::SPAN_PUSH, service: @sidekiq_service) do |span|
             span.resource = resource
+            Contrib::Sampling.set_event_sample_rate(span, configuration[:event_sample_rate])
             span.set_tag(Ext::TAG_JOB_ID, job['jid'])
             span.set_tag(Ext::TAG_JOB_QUEUE, job['queue'])
             span.set_tag(Ext::TAG_JOB_WRAPPER, job['class']) if job['wrapped']
@@ -29,6 +29,12 @@ def call(worker_class, job, queue, redis_pool)
             yield
           end
         end
+
+        private
+
+        def configuration
+          Datadog.configuration[:sidekiq]
+        end
       end
     end
   end
diff --git a/lib/ddtrace/contrib/sidekiq/server_tracer.rb b/lib/ddtrace/contrib/sidekiq/server_tracer.rb
index f85108c6f22..cfb200e0b29 100644
--- a/lib/ddtrace/contrib/sidekiq/server_tracer.rb
+++ b/lib/ddtrace/contrib/sidekiq/server_tracer.rb
@@ -1,4 +1,5 @@
 require 'ddtrace/contrib/sidekiq/tracing'
+require 'ddtrace/contrib/sampling'
 
 module Datadog
   module Contrib
@@ -9,7 +10,7 @@ class ServerTracer
 
         def initialize(options = {})
           super
-          @sidekiq_service = options[:service_name] || Datadog.configuration[:sidekiq][:service_name]
+          @sidekiq_service = options[:service_name] || configuration[:service_name]
         end
 
         def call(worker, job, queue)
@@ -20,6 +21,7 @@ def call(worker, job, queue)
 
           @tracer.trace(Ext::SPAN_JOB, service: service, span_type: Datadog::Ext::AppTypes::WORKER) do |span|
             span.resource = resource
+            Contrib::Sampling.set_event_sample_rate(span, configuration[:event_sample_rate])
             span.set_tag(Ext::TAG_JOB_ID, job['jid'])
             span.set_tag(Ext::TAG_JOB_RETRY, job['retry'])
             span.set_tag(Ext::TAG_JOB_QUEUE, job['queue'])
@@ -32,6 +34,10 @@ def call(worker, job, queue)
 
         private
 
+        def configuration
+          Datadog.configuration[:sidekiq]
+        end
+
         def service_from_worker_config(resource)
           # Try to get the Ruby class from the resource name.
           worker_klass = begin
diff --git a/lib/ddtrace/contrib/sucker_punch/instrumentation.rb b/lib/ddtrace/contrib/sucker_punch/instrumentation.rb
index 67d238fb0a8..f8a54e41edf 100644
--- a/lib/ddtrace/contrib/sucker_punch/instrumentation.rb
+++ b/lib/ddtrace/contrib/sucker_punch/instrumentation.rb
@@ -1,4 +1,5 @@
 require 'sucker_punch'
+require 'ddtrace/contrib/sampling'
 require 'ddtrace/contrib/sucker_punch/ext'
 
 module Datadog
@@ -18,6 +19,7 @@ def __run_perform(*args)
 
               __with_instrumentation(Ext::SPAN_PERFORM) do |span|
                 span.resource = "PROCESS #{self}"
+                Contrib::Sampling.set_event_sample_rate(span, datadog_configuration[:event_sample_rate])
                 __run_perform_without_datadog(*args)
               end
             rescue => e
@@ -43,6 +45,10 @@ def perform_in(interval, *args)
 
             private
 
+            def datadog_configuration
+              Datadog.configuration[:sucker_punch]
+            end
+
             def __with_instrumentation(name)
               pin = Datadog::Pin.get_from(::SuckerPunch)
 
diff --git a/lib/ddtrace/correlation.rb b/lib/ddtrace/correlation.rb
new file mode 100644
index 00000000000..a23232bd537
--- /dev/null
+++ b/lib/ddtrace/correlation.rb
@@ -0,0 +1,32 @@
+module Datadog
+  # Contains behavior for managing correlations with tracing
+  # e.g. Retrieve a correlation to the current trace for logging, etc.
+  module Correlation
+    # Struct representing correlation
+    Identifier = Struct.new(:trace_id, :span_id).tap do |struct|
+      # Do this #class_eval here for Ruby 1.9.3 support.
+      # Ruby 2.0+ supports passing a block to Struct::new instead.
+      struct.class_eval do
+        def initialize(*args)
+          super
+          self.trace_id = trace_id || 0
+          self.span_id = span_id || 0
+        end
+
+        def to_s
+          "dd.trace_id=#{trace_id} dd.span_id=#{span_id}"
+        end
+      end
+    end.freeze
+
+    NULL_IDENTIFIER = Identifier.new.freeze
+
+    module_function
+
+    # Produces a CorrelationIdentifier from the Context provided
+    def identifier_from_context(context)
+      return NULL_IDENTIFIER if context.nil?
+      Identifier.new(context.trace_id, context.span_id).freeze
+    end
+  end
+end
diff --git a/lib/ddtrace/ext/priority.rb b/lib/ddtrace/ext/priority.rb
index 711b597c296..781f015bf4b 100644
--- a/lib/ddtrace/ext/priority.rb
+++ b/lib/ddtrace/ext/priority.rb
@@ -3,6 +3,8 @@ module Ext
     # Priority is a hint given to the backend so that it knows which traces to reject or kept.
     # In a distributed context, it should be set before any context propagation (fork, RPC calls) to be effective.
     module Priority
+      # Tag for span sample rate; used by agent to determine whether event is emitted.
+      TAG_EVENT_SAMPLE_RATE = '_dd1.sr.eausr'.freeze
       # Use this to explicitely inform the backend that a trace should be rejected and not stored.
       USER_REJECT = -1
       # Used by the builtin sampler to inform the backend that a trace should be rejected and not stored.
diff --git a/lib/ddtrace/tracer.rb b/lib/ddtrace/tracer.rb
index 9aa97a6cd04..b94afbd752e 100644
--- a/lib/ddtrace/tracer.rb
+++ b/lib/ddtrace/tracer.rb
@@ -10,6 +10,7 @@
 require 'ddtrace/logger'
 require 'ddtrace/writer'
 require 'ddtrace/sampler'
+require 'ddtrace/correlation'
 
 # \Datadog global namespace that includes all tracing functionality for Tracer and Span classes.
 module Datadog
@@ -126,7 +127,7 @@ def configure(options = {})
 
       # Those are rare "power-user" options.
       sampler = options.fetch(:sampler, nil)
-      priority_sampling = options[:priority_sampling]
+      priority_sampling = options.fetch(:priority_sampling, nil)
       max_spans_before_partial_flush = options.fetch(:max_spans_before_partial_flush, nil)
       min_spans_before_partial_flush = options.fetch(:min_spans_before_partial_flush, nil)
       partial_flush_timeout = options.fetch(:partial_flush_timeout, nil)
@@ -134,9 +135,15 @@ def configure(options = {})
       @enabled = enabled unless enabled.nil?
       @sampler = sampler unless sampler.nil?
 
-      if priority_sampling
+      # Re-build the sampler and writer if priority sampling is enabled,
+      # but neither are configured. Verify the sampler isn't already a
+      # priority sampler too, so we don't wrap one with another.
+      if priority_sampling != false && !@sampler.is_a?(PrioritySampler)
         @sampler = PrioritySampler.new(base_sampler: @sampler)
         @writer = Writer.new(priority_sampler: @sampler)
+      elsif priority_sampling == false
+        @sampler = sampler || Datadog::AllSampler.new if @sampler.is_a?(PrioritySampler)
+        @writer = Writer.new
       end
 
       @writer.transport.hostname = hostname unless hostname.nil?
@@ -351,6 +358,11 @@ def active_root_span
       call_context.current_root_span
     end
 
+    # Return a CorrelationIdentifier for active span
+    def active_correlation
+      Datadog::Correlation.identifier_from_context(call_context)
+    end
+
     # Send the trace to the writer to enqueue the spans list in the agent
     # sending queue.
     def write(trace)
diff --git a/lib/ddtrace/version.rb b/lib/ddtrace/version.rb
index 141ccaa34ee..53b970c36a7 100644
--- a/lib/ddtrace/version.rb
+++ b/lib/ddtrace/version.rb
@@ -1,8 +1,8 @@
 module Datadog
   module VERSION
     MAJOR = 0
-    MINOR = 18
-    PATCH = 3
+    MINOR = 19
+    PATCH = 0
     PRE = nil
 
     STRING = [MAJOR, MINOR, PATCH, PRE].compact.join('.')
diff --git a/spec/ddtrace/configuration/pin_setup_spec.rb b/spec/ddtrace/configuration/pin_setup_spec.rb
index ab3bbf732f0..d9d3d89bf0f 100644
--- a/spec/ddtrace/configuration/pin_setup_spec.rb
+++ b/spec/ddtrace/configuration/pin_setup_spec.rb
@@ -24,7 +24,7 @@
         }
       end
 
-      let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+      let(:tracer) { get_test_tracer }
 
       it do
         expect(target.datadog_pin.service).to eq('my-service')
diff --git a/spec/ddtrace/context_spec.rb b/spec/ddtrace/context_spec.rb
index acf986d598b..677df748037 100644
--- a/spec/ddtrace/context_spec.rb
+++ b/spec/ddtrace/context_spec.rb
@@ -5,7 +5,7 @@
 RSpec.describe Datadog::Context do
   subject(:context) { described_class.new(options) }
   let(:options) { {} }
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   describe '#current_root_span' do
     subject(:current_root_span) { context.current_root_span }
diff --git a/spec/ddtrace/contrib/active_model_serializers/patcher_spec.rb b/spec/ddtrace/contrib/active_model_serializers/patcher_spec.rb
index eb17b8d37d2..28ddf0c5ff8 100644
--- a/spec/ddtrace/contrib/active_model_serializers/patcher_spec.rb
+++ b/spec/ddtrace/contrib/active_model_serializers/patcher_spec.rb
@@ -10,7 +10,7 @@
 RSpec.describe 'ActiveModelSerializers patcher' do
   include_context 'AMS serializer'
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   def all_spans
     tracer.writer.spans(:keep)
diff --git a/spec/ddtrace/contrib/active_record/multi_db_spec.rb b/spec/ddtrace/contrib/active_record/multi_db_spec.rb
index 18dbf955f70..924b2df1a1c 100644
--- a/spec/ddtrace/contrib/active_record/multi_db_spec.rb
+++ b/spec/ddtrace/contrib/active_record/multi_db_spec.rb
@@ -6,7 +6,7 @@
 require 'sqlite3'
 
 RSpec.describe 'ActiveRecord multi-database implementation' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:configuration_options) { { tracer: tracer, service_name: default_db_service_name } }
   let(:default_db_service_name) { 'default-db' }
 
diff --git a/spec/ddtrace/contrib/active_record/performance_spec.rb b/spec/ddtrace/contrib/active_record/performance_spec.rb
index a1b4aac1f3d..aee3eaba788 100644
--- a/spec/ddtrace/contrib/active_record/performance_spec.rb
+++ b/spec/ddtrace/contrib/active_record/performance_spec.rb
@@ -5,7 +5,7 @@
 require 'sqlite3'
 
 RSpec.describe 'ActiveRecord tracing performance' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:options) { { tracer: tracer } }
   let(:spans) { tracer.writer.spans }
 
diff --git a/spec/ddtrace/contrib/active_record/tracer_spec.rb b/spec/ddtrace/contrib/active_record/tracer_spec.rb
index 8ea9f479951..decef947731 100644
--- a/spec/ddtrace/contrib/active_record/tracer_spec.rb
+++ b/spec/ddtrace/contrib/active_record/tracer_spec.rb
@@ -4,7 +4,7 @@
 require_relative 'app'
 
 RSpec.describe 'ActiveRecord instrumentation' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:configuration_options) { { tracer: tracer } }
 
   before(:each) do
diff --git a/spec/ddtrace/contrib/active_support/notifications/subscription_spec.rb b/spec/ddtrace/contrib/active_support/notifications/subscription_spec.rb
index afee9f296e1..3e6fd6b27db 100644
--- a/spec/ddtrace/contrib/active_support/notifications/subscription_spec.rb
+++ b/spec/ddtrace/contrib/active_support/notifications/subscription_spec.rb
@@ -7,7 +7,7 @@
 RSpec.describe Datadog::Contrib::ActiveSupport::Notifications::Subscription do
   describe 'instance' do
     subject(:subscription) { described_class.new(tracer, span_name, options, &block) }
-    let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+    let(:tracer) { get_test_tracer }
     let(:span_name) { double('span_name') }
     let(:options) { {} }
     let(:payload) { {} }
diff --git a/spec/ddtrace/contrib/aws/instrumentation_spec.rb b/spec/ddtrace/contrib/aws/instrumentation_spec.rb
index a7eed337119..36a46f61aea 100644
--- a/spec/ddtrace/contrib/aws/instrumentation_spec.rb
+++ b/spec/ddtrace/contrib/aws/instrumentation_spec.rb
@@ -6,7 +6,7 @@
 require 'ddtrace/ext/http'
 
 RSpec.describe 'AWS instrumentation' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:client) { ::Aws::S3::Client.new(stub_responses: responses) }
   let(:responses) { true }
diff --git a/spec/ddtrace/contrib/concurrent_ruby/integration_spec.rb b/spec/ddtrace/contrib/concurrent_ruby/integration_spec.rb
index b32bae667ad..0ea383c421b 100644
--- a/spec/ddtrace/contrib/concurrent_ruby/integration_spec.rb
+++ b/spec/ddtrace/contrib/concurrent_ruby/integration_spec.rb
@@ -12,7 +12,7 @@
     remove_patch!(:concurrent_ruby)
   end
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:configuration_options) { { tracer: tracer } }
 
   subject(:deferred_execution) do
diff --git a/spec/ddtrace/contrib/configuration/settings_spec.rb b/spec/ddtrace/contrib/configuration/settings_spec.rb
index cf80e41aeb7..20581b48d13 100644
--- a/spec/ddtrace/contrib/configuration/settings_spec.rb
+++ b/spec/ddtrace/contrib/configuration/settings_spec.rb
@@ -9,7 +9,23 @@
 
   describe '#options' do
     subject(:options) { settings.options }
-    it { is_expected.to include(:service_name) }
-    it { is_expected.to include(:tracer) }
+
+    describe ':service_name' do
+      subject(:option) { options[:service_name] }
+      it { expect(options).to include(:service_name) }
+      it { expect(option.get).to be nil }
+    end
+
+    describe ':tracer' do
+      subject(:option) { options[:tracer] }
+      it { expect(options).to include(:tracer) }
+      it { expect(option.get).to be Datadog.tracer }
+    end
+
+    describe ':event_sample_rate' do
+      subject(:option) { options[:event_sample_rate] }
+      it { expect(options).to include(:event_sample_rate) }
+      it { expect(option.get).to be nil }
+    end
   end
 end
diff --git a/spec/ddtrace/contrib/dalli/instrumentation_spec.rb b/spec/ddtrace/contrib/dalli/instrumentation_spec.rb
index f6592f73c46..a626ecb6b26 100644
--- a/spec/ddtrace/contrib/dalli/instrumentation_spec.rb
+++ b/spec/ddtrace/contrib/dalli/instrumentation_spec.rb
@@ -9,7 +9,7 @@
   let(:test_port) { ENV.fetch('TEST_MEMCACHED_PORT', '11211') }
 
   let(:client) { ::Dalli::Client.new("#{test_host}:#{test_port}") }
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:pin) { ::Dalli.datadog_pin }
 
   def all_spans
diff --git a/spec/ddtrace/contrib/delayed_job/plugin_spec.rb b/spec/ddtrace/contrib/delayed_job/plugin_spec.rb
index 23a70b01f69..530894d7db5 100644
--- a/spec/ddtrace/contrib/delayed_job/plugin_spec.rb
+++ b/spec/ddtrace/contrib/delayed_job/plugin_spec.rb
@@ -1,4 +1,6 @@
 require 'spec_helper'
+require 'ddtrace/contrib/sampling_examples'
+
 require 'active_record'
 require 'delayed_job'
 require 'delayed_job_active_record'
@@ -24,14 +26,16 @@ def job_data
     end)
   end
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
+  let(:configuration_options) { { tracer: tracer } }
 
   before do
-    Datadog.configure { |c| c.use :delayed_job, tracer: tracer }
-
+    Datadog.configure { |c| c.use :delayed_job, configuration_options }
     Delayed::Worker.delay_jobs = false
   end
 
+  after(:each) { Datadog.registry[:delayed_job].reset_configuration! }
+
   describe 'instrumenting worker execution' do
     let(:worker) { double(:worker, name: 'worker') }
     before do
@@ -100,6 +104,8 @@ def job_data
         expect(span.get_tag('delayed_job.attempts')).to eq('0')
       end
 
+      it_behaves_like 'event sample rate'
+
       context 'when queue name is set' do
         let(:queue_name) { 'queue_name' }
         let(:job_params) { { queue: queue_name } }
diff --git a/spec/ddtrace/contrib/elasticsearch/patcher_spec.rb b/spec/ddtrace/contrib/elasticsearch/patcher_spec.rb
index e8798fea60e..2ad06417758 100644
--- a/spec/ddtrace/contrib/elasticsearch/patcher_spec.rb
+++ b/spec/ddtrace/contrib/elasticsearch/patcher_spec.rb
@@ -9,7 +9,7 @@
 
   let(:client) { Elasticsearch::Client.new(url: server) }
   let(:pin) { Datadog::Pin.get_from(client) }
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   before do
     Datadog.configure do |c|
diff --git a/spec/ddtrace/contrib/elasticsearch/transport_spec.rb b/spec/ddtrace/contrib/elasticsearch/transport_spec.rb
index dbe5206a475..e93b747b0f2 100644
--- a/spec/ddtrace/contrib/elasticsearch/transport_spec.rb
+++ b/spec/ddtrace/contrib/elasticsearch/transport_spec.rb
@@ -22,7 +22,7 @@
   let(:server) { "http://#{host}:#{port}" }
 
   let(:client) { Elasticsearch::Client.new(url: server) }
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:spans) { tracer.writer.spans }
   let(:span) { spans.first }
diff --git a/spec/ddtrace/contrib/excon/instrumentation_spec.rb b/spec/ddtrace/contrib/excon/instrumentation_spec.rb
index 9ab1d64abf0..452c2b7f73a 100644
--- a/spec/ddtrace/contrib/excon/instrumentation_spec.rb
+++ b/spec/ddtrace/contrib/excon/instrumentation_spec.rb
@@ -5,7 +5,7 @@
 require 'ddtrace/contrib/excon/middleware'
 
 RSpec.describe Datadog::Contrib::Excon::Middleware do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:connection_options) { { mock: true } }
   let(:middleware_options) { {} }
diff --git a/spec/ddtrace/contrib/faraday/middleware_spec.rb b/spec/ddtrace/contrib/faraday/middleware_spec.rb
index 04dc8bc6547..469c0dfa2bb 100644
--- a/spec/ddtrace/contrib/faraday/middleware_spec.rb
+++ b/spec/ddtrace/contrib/faraday/middleware_spec.rb
@@ -5,7 +5,7 @@
 require 'ddtrace/ext/distributed'
 
 RSpec.describe 'Faraday middleware' do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:client) do
     ::Faraday.new('http://example.com') do |builder|
diff --git a/spec/ddtrace/contrib/graphql/tracer_spec.rb b/spec/ddtrace/contrib/graphql/tracer_spec.rb
index 32c2e8af07a..9cb6651538f 100644
--- a/spec/ddtrace/contrib/graphql/tracer_spec.rb
+++ b/spec/ddtrace/contrib/graphql/tracer_spec.rb
@@ -14,7 +14,7 @@
     end
   end
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   def pop_spans
     tracer.writer.spans(:keep)
diff --git a/spec/ddtrace/contrib/http/patcher_spec.rb b/spec/ddtrace/contrib/http/patcher_spec.rb
index 69dd7ff040d..e65b596f497 100644
--- a/spec/ddtrace/contrib/http/patcher_spec.rb
+++ b/spec/ddtrace/contrib/http/patcher_spec.rb
@@ -3,7 +3,7 @@
 require 'net/http'
 
 RSpec.describe 'net/http patcher' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:host) { 'example.com' }
 
   before do
diff --git a/spec/ddtrace/contrib/mongodb/client_spec.rb b/spec/ddtrace/contrib/mongodb/client_spec.rb
index d3ed752c944..6a51b316dd1 100644
--- a/spec/ddtrace/contrib/mongodb/client_spec.rb
+++ b/spec/ddtrace/contrib/mongodb/client_spec.rb
@@ -4,7 +4,7 @@
 require 'mongo'
 
 RSpec.describe 'Mongo::Client instrumentation' do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:client) { Mongo::Client.new(["#{host}:#{port}"], client_options) }
   let(:client_options) { { database: database } }
diff --git a/spec/ddtrace/contrib/mysql2/patcher_spec.rb b/spec/ddtrace/contrib/mysql2/patcher_spec.rb
index 44924f94219..c68e67f6691 100644
--- a/spec/ddtrace/contrib/mysql2/patcher_spec.rb
+++ b/spec/ddtrace/contrib/mysql2/patcher_spec.rb
@@ -4,7 +4,7 @@
 require 'mysql2'
 
 RSpec.describe 'Mysql2::Client patcher' do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:client) do
     Mysql2::Client.new(
diff --git a/spec/ddtrace/contrib/racecar/patcher_spec.rb b/spec/ddtrace/contrib/racecar/patcher_spec.rb
index 2679b4f87f0..4ee5c04ab25 100644
--- a/spec/ddtrace/contrib/racecar/patcher_spec.rb
+++ b/spec/ddtrace/contrib/racecar/patcher_spec.rb
@@ -1,11 +1,13 @@
 require 'spec_helper'
+require 'ddtrace/contrib/sampling_examples'
 
 require 'racecar'
 require 'racecar/cli'
 require 'active_support'
 require 'ddtrace'
 RSpec.describe 'Racecar patcher' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
+  let(:configuration_options) { { tracer: tracer } }
 
   def all_spans
     tracer.writer.spans(:keep)
@@ -13,10 +15,12 @@ def all_spans
 
   before(:each) do
     Datadog.configure do |c|
-      c.use :racecar, tracer: tracer
+      c.use :racecar, configuration_options
     end
   end
 
+  after(:each) { Datadog.registry[:racecar].reset_configuration! }
+
   describe 'for single message processing' do
     let(:topic) { 'dd_trace_test_dummy' }
     let(:consumer) { 'DummyConsumer' }
@@ -31,7 +35,7 @@ def all_spans
       }
     end
 
-    let(:racecar_span) do
+    let(:span) do
       all_spans.select { |s| s.name == Datadog::Contrib::Racecar::Ext::SPAN_MESSAGE }.first
     end
 
@@ -39,7 +43,7 @@ def all_spans
       it 'is expected to send a span' do
         ActiveSupport::Notifications.instrument('process_message.racecar', payload)
 
-        racecar_span.tap do |span|
+        span.tap do |span|
           expect(span).to_not be nil
           expect(span.service).to eq('racecar')
           expect(span.name).to eq('racecar.message')
@@ -67,7 +71,7 @@ def all_spans
           nil
         end
 
-        racecar_span.tap do |span|
+        span.tap do |span|
           expect(span).to_not be nil
           expect(span.service).to eq('racecar')
           expect(span.name).to eq('racecar.message')
@@ -81,6 +85,10 @@ def all_spans
         end
       end
     end
+
+    it_behaves_like 'event sample rate' do
+      before { ActiveSupport::Notifications.instrument('process_message.racecar', payload) }
+    end
   end
 
   describe 'for batch message processing' do
@@ -99,7 +107,7 @@ def all_spans
       }
     end
 
-    let(:racecar_span) do
+    let(:span) do
       all_spans.select { |s| s.name == Datadog::Contrib::Racecar::Ext::SPAN_BATCH }.first
     end
 
@@ -107,7 +115,7 @@ def all_spans
       it 'is expected to send a span' do
         ActiveSupport::Notifications.instrument('process_batch.racecar', payload)
 
-        racecar_span.tap do |span|
+        span.tap do |span|
           expect(span).to_not be nil
           expect(span.service).to eq('racecar')
           expect(span.name).to eq('racecar.batch')
@@ -135,7 +143,7 @@ def all_spans
           nil
         end
 
-        racecar_span.tap do |span|
+        span.tap do |span|
           expect(span).to_not be nil
           expect(span.service).to eq('racecar')
           expect(span.name).to eq('racecar.batch')
@@ -150,5 +158,9 @@ def all_spans
         end
       end
     end
+
+    it_behaves_like 'event sample rate' do
+      before { ActiveSupport::Notifications.instrument('process_batch.racecar', payload) }
+    end
   end
 end
diff --git a/spec/ddtrace/contrib/rack/configuration_spec.rb b/spec/ddtrace/contrib/rack/configuration_spec.rb
new file mode 100644
index 00000000000..acfbadea959
--- /dev/null
+++ b/spec/ddtrace/contrib/rack/configuration_spec.rb
@@ -0,0 +1,187 @@
+require 'spec_helper'
+require 'ddtrace/contrib/sampling_examples'
+require 'rack/test'
+
+require 'rack'
+require 'ddtrace'
+require 'ddtrace/contrib/rack/middlewares'
+
+RSpec.describe 'Rack integration configuration' do
+  include Rack::Test::Methods
+
+  let(:tracer) { get_test_tracer }
+  let(:configuration_options) { { tracer: tracer } }
+
+  let(:spans) { tracer.writer.spans }
+  let(:span) { spans.first }
+
+  before(:each) do
+    Datadog.configure do |c|
+      c.use :rack, configuration_options
+    end
+  end
+
+  after(:each) { Datadog.registry[:rack].reset_configuration! }
+
+  shared_context 'an incoming HTTP request' do
+    subject(:response) { get '/' }
+
+    let(:app) do
+      Rack::Builder.new do
+        use Datadog::Contrib::Rack::TraceMiddleware
+
+        map '/' do
+          run(proc { |_env| [200, { 'Content-Type' => 'text/html' }, 'OK'] })
+        end
+      end.to_app
+    end
+  end
+
+  it_behaves_like 'event sample rate' do
+    include_context 'an incoming HTTP request'
+    before { is_expected.to be_ok }
+  end
+
+  describe 'request queueing' do
+    shared_context 'queue header' do
+      let(:queue_value) { "t=#{queue_time}" }
+      let(:queue_time) { (Time.now.utc - 5).to_i }
+
+      before(:each) do
+        header queue_header, queue_value
+      end
+    end
+
+    shared_context 'no queue header' do
+      let(:queue_header) { nil }
+      let(:queue_value) { nil }
+    end
+
+    shared_examples_for 'a Rack request with queuing' do
+      let(:queue_span) { spans.first }
+      let(:rack_span) { spans.last }
+
+      it 'produces a queued Rack trace' do
+        is_expected.to be_ok
+        expect(spans).to have(2).items
+
+        expect(queue_span.name).to eq('http_server.queue')
+        expect(queue_span.service).to eq(Datadog.configuration[:rack][:web_service_name])
+        expect(queue_span.start_time.to_i).to eq(queue_time)
+
+        expect(rack_span.name).to eq('rack.request')
+        expect(rack_span.span_type).to eq('http')
+        expect(rack_span.service).to eq(Datadog.configuration[:rack][:service_name])
+        expect(rack_span.resource).to eq('GET 200')
+        expect(rack_span.get_tag('http.method')).to eq('GET')
+        expect(rack_span.get_tag('http.status_code')).to eq('200')
+        expect(rack_span.get_tag('http.url')).to eq('/')
+        expect(rack_span.status).to eq(0)
+
+        expect(queue_span.span_id).to eq(rack_span.parent_id)
+      end
+    end
+
+    shared_examples_for 'a Rack request without queuing' do
+      it 'produces a non-queued Rack trace' do
+        is_expected.to be_ok
+        expect(spans).to have(1).items
+
+        expect(span).to_not be nil
+        expect(span.name).to eq('rack.request')
+        expect(span.span_type).to eq('http')
+        expect(span.service).to eq(Datadog.configuration[:rack][:service_name])
+        expect(span.resource).to eq('GET 200')
+        expect(span.get_tag('http.method')).to eq('GET')
+        expect(span.get_tag('http.status_code')).to eq('200')
+        expect(span.get_tag('http.url')).to eq('/')
+        expect(span.status).to eq(0)
+
+        expect(span.parent_id).to eq(0)
+      end
+    end
+
+    context 'when enabled' do
+      let(:configuration_options) { super().merge(request_queuing: true) }
+
+      context 'and a request is received' do
+        include_context 'an incoming HTTP request'
+
+        context 'with X-Request-Start header' do
+          include_context 'queue header' do
+            let(:queue_header) { 'X-Request-Start' }
+          end
+
+          it_behaves_like 'a Rack request with queuing'
+
+          context 'given a custom web service name' do
+            let(:configuration_options) { super().merge(web_service_name: web_service_name) }
+            let(:web_service_name) { 'nginx' }
+
+            it_behaves_like 'a Rack request with queuing' do
+              it 'sets the custom service name' do
+                is_expected.to be_ok
+                expect(queue_span.service).to eq(web_service_name)
+              end
+            end
+          end
+        end
+
+        context 'with X-Queue-Start header' do
+          include_context 'queue header' do
+            let(:queue_header) { 'X-Queue-Start' }
+          end
+
+          it_behaves_like 'a Rack request with queuing'
+        end
+
+        # Ensure a queuing Span is NOT created if there is a clock skew
+        # where the starting time is greater than current host Time.now
+        context 'with a skewed queue header' do
+          before(:each) { header 'X-Request-Start', (Time.now.utc + 5).to_i }
+          it_behaves_like 'a Rack request without queuing'
+        end
+
+        # Ensure a queuing Span is NOT created if the header is wrong
+        context 'with a invalid queue header' do
+          before(:each) { header 'X-Request-Start', 'foobar' }
+          it_behaves_like 'a Rack request without queuing'
+        end
+
+        context 'without queue header' do
+          include_context 'no queue header'
+          it_behaves_like 'a Rack request without queuing'
+        end
+      end
+    end
+
+    context 'when disabled' do
+      let(:configuration_options) { super().merge(request_queuing: false) }
+
+      context 'and a request is received' do
+        include_context 'an incoming HTTP request'
+
+        context 'with X-Request-Start header' do
+          include_context 'queue header' do
+            let(:queue_header) { 'X-Request-Start' }
+          end
+
+          it_behaves_like 'a Rack request without queuing'
+        end
+
+        context 'with X-Queue-Start header' do
+          include_context 'queue header' do
+            let(:queue_header) { 'X-Queue-Start' }
+          end
+
+          it_behaves_like 'a Rack request without queuing'
+        end
+
+        context 'without queue header' do
+          include_context 'no queue header'
+          it_behaves_like 'a Rack request without queuing'
+        end
+      end
+    end
+  end
+end
diff --git a/spec/ddtrace/contrib/rack/distributed_spec.rb b/spec/ddtrace/contrib/rack/distributed_spec.rb
index 63bef3fbb5f..de13aa804b4 100644
--- a/spec/ddtrace/contrib/rack/distributed_spec.rb
+++ b/spec/ddtrace/contrib/rack/distributed_spec.rb
@@ -8,7 +8,7 @@
 RSpec.describe 'Rack integration distributed tracing' do
   include Rack::Test::Methods
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:rack_options) { { tracer: tracer } }
 
   let(:spans) { tracer.writer.spans }
diff --git a/spec/ddtrace/contrib/rack/integration_spec.rb b/spec/ddtrace/contrib/rack/integration_spec.rb
index 900161789cc..e2e9aa1a745 100644
--- a/spec/ddtrace/contrib/rack/integration_spec.rb
+++ b/spec/ddtrace/contrib/rack/integration_spec.rb
@@ -9,7 +9,7 @@
 RSpec.describe 'Rack integration tests' do
   include Rack::Test::Methods
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:rack_options) { { tracer: tracer } }
 
   let(:spans) { tracer.writer.spans }
diff --git a/spec/ddtrace/contrib/rack/middleware_spec.rb b/spec/ddtrace/contrib/rack/middleware_spec.rb
index b9a2101eb9b..7d965d6d9e4 100644
--- a/spec/ddtrace/contrib/rack/middleware_spec.rb
+++ b/spec/ddtrace/contrib/rack/middleware_spec.rb
@@ -8,7 +8,7 @@
   subject(:middleware) { described_class.new(app) }
   let(:app) { instance_double(Rack::Builder) }
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:configuration_options) { { tracer: tracer } }
 
   before(:each) do
diff --git a/spec/ddtrace/contrib/rack/request_queuing_spec.rb b/spec/ddtrace/contrib/rack/request_queuing_spec.rb
deleted file mode 100644
index c6f9f9b014d..00000000000
--- a/spec/ddtrace/contrib/rack/request_queuing_spec.rb
+++ /dev/null
@@ -1,179 +0,0 @@
-require 'spec_helper'
-require 'rack/test'
-
-require 'rack'
-require 'ddtrace'
-require 'ddtrace/contrib/rack/middlewares'
-
-RSpec.describe 'Rack integration request queuing' do
-  include Rack::Test::Methods
-
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
-  let(:rack_options) { { tracer: tracer } }
-
-  let(:spans) { tracer.writer.spans }
-  let(:span) { spans.first }
-
-  before(:each) do
-    Datadog.configure do |c|
-      c.use :rack, rack_options
-    end
-  end
-
-  after(:each) { Datadog.registry[:rack].reset_configuration! }
-
-  shared_context 'an incoming HTTP request' do
-    subject(:response) { get '/' }
-
-    let(:app) do
-      Rack::Builder.new do
-        use Datadog::Contrib::Rack::TraceMiddleware
-
-        map '/' do
-          run(proc { |_env| [200, { 'Content-Type' => 'text/html' }, 'OK'] })
-        end
-      end.to_app
-    end
-  end
-
-  shared_context 'queue header' do
-    let(:queue_value) { "t=#{queue_time}" }
-    let(:queue_time) { (Time.now.utc - 5).to_i }
-
-    before(:each) do
-      header queue_header, queue_value
-    end
-  end
-
-  shared_context 'no queue header' do
-    let(:queue_header) { nil }
-    let(:queue_value) { nil }
-  end
-
-  shared_examples_for 'a Rack request with queuing' do
-    let(:queue_span) { spans.first }
-    let(:rack_span) { spans.last }
-
-    it 'produces a queued Rack trace' do
-      is_expected.to be_ok
-      expect(spans).to have(2).items
-
-      expect(queue_span.name).to eq('http_server.queue')
-      expect(queue_span.service).to eq(Datadog.configuration[:rack][:web_service_name])
-      expect(queue_span.start_time.to_i).to eq(queue_time)
-
-      expect(rack_span.name).to eq('rack.request')
-      expect(rack_span.span_type).to eq('http')
-      expect(rack_span.service).to eq(Datadog.configuration[:rack][:service_name])
-      expect(rack_span.resource).to eq('GET 200')
-      expect(rack_span.get_tag('http.method')).to eq('GET')
-      expect(rack_span.get_tag('http.status_code')).to eq('200')
-      expect(rack_span.get_tag('http.url')).to eq('/')
-      expect(rack_span.status).to eq(0)
-
-      expect(queue_span.span_id).to eq(rack_span.parent_id)
-    end
-  end
-
-  shared_examples_for 'a Rack request without queuing' do
-    it 'produces a non-queued Rack trace' do
-      is_expected.to be_ok
-      expect(spans).to have(1).items
-
-      expect(span).to_not be nil
-      expect(span.name).to eq('rack.request')
-      expect(span.span_type).to eq('http')
-      expect(span.service).to eq(Datadog.configuration[:rack][:service_name])
-      expect(span.resource).to eq('GET 200')
-      expect(span.get_tag('http.method')).to eq('GET')
-      expect(span.get_tag('http.status_code')).to eq('200')
-      expect(span.get_tag('http.url')).to eq('/')
-      expect(span.status).to eq(0)
-
-      expect(span.parent_id).to eq(0)
-    end
-  end
-
-  context 'when enabled' do
-    let(:rack_options) { super().merge(request_queuing: true) }
-
-    context 'and a request is received' do
-      include_context 'an incoming HTTP request'
-
-      context 'with X-Request-Start header' do
-        include_context 'queue header' do
-          let(:queue_header) { 'X-Request-Start' }
-        end
-
-        it_behaves_like 'a Rack request with queuing'
-
-        context 'given a custom web service name' do
-          let(:rack_options) { super().merge(web_service_name: web_service_name) }
-          let(:web_service_name) { 'nginx' }
-
-          it_behaves_like 'a Rack request with queuing' do
-            it 'sets the custom service name' do
-              is_expected.to be_ok
-              expect(queue_span.service).to eq(web_service_name)
-            end
-          end
-        end
-      end
-
-      context 'with X-Queue-Start header' do
-        include_context 'queue header' do
-          let(:queue_header) { 'X-Queue-Start' }
-        end
-
-        it_behaves_like 'a Rack request with queuing'
-      end
-
-      # Ensure a queuing Span is NOT created if there is a clock skew
-      # where the starting time is greater than current host Time.now
-      context 'with a skewed queue header' do
-        before(:each) { header 'X-Request-Start', (Time.now.utc + 5).to_i }
-        it_behaves_like 'a Rack request without queuing'
-      end
-
-      # Ensure a queuing Span is NOT created if the header is wrong
-      context 'with a invalid queue header' do
-        before(:each) { header 'X-Request-Start', 'foobar' }
-        it_behaves_like 'a Rack request without queuing'
-      end
-
-      context 'without queue header' do
-        include_context 'no queue header'
-        it_behaves_like 'a Rack request without queuing'
-      end
-    end
-  end
-
-  context 'when disabled' do
-    let(:rack_options) { super().merge(request_queuing: false) }
-
-    context 'and a request is received' do
-      include_context 'an incoming HTTP request'
-
-      context 'with X-Request-Start header' do
-        include_context 'queue header' do
-          let(:queue_header) { 'X-Request-Start' }
-        end
-
-        it_behaves_like 'a Rack request without queuing'
-      end
-
-      context 'with X-Queue-Start header' do
-        include_context 'queue header' do
-          let(:queue_header) { 'X-Queue-Start' }
-        end
-
-        it_behaves_like 'a Rack request without queuing'
-      end
-
-      context 'without queue header' do
-        include_context 'no queue header'
-        it_behaves_like 'a Rack request without queuing'
-      end
-    end
-  end
-end
diff --git a/spec/ddtrace/contrib/rack/resource_name_spec.rb b/spec/ddtrace/contrib/rack/resource_name_spec.rb
index f9bc60f650d..190b7e1624d 100644
--- a/spec/ddtrace/contrib/rack/resource_name_spec.rb
+++ b/spec/ddtrace/contrib/rack/resource_name_spec.rb
@@ -8,7 +8,7 @@
 RSpec.describe 'Rack integration with other middleware' do
   include Rack::Test::Methods
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:rack_options) do
     {
       application: app,
diff --git a/spec/ddtrace/contrib/rails/action_controller_spec.rb b/spec/ddtrace/contrib/rails/action_controller_spec.rb
index f6f65f1ec5e..af852c237aa 100644
--- a/spec/ddtrace/contrib/rails/action_controller_spec.rb
+++ b/spec/ddtrace/contrib/rails/action_controller_spec.rb
@@ -1,7 +1,7 @@
 require 'ddtrace/contrib/rails/rails_helper'
 
 RSpec.describe 'ActionController tracing' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:rails_options) { { tracer: tracer } }
 
   before(:each) do
diff --git a/spec/ddtrace/contrib/rails/middleware_spec.rb b/spec/ddtrace/contrib/rails/middleware_spec.rb
index d9baf2dc101..e20fe8b7bfb 100644
--- a/spec/ddtrace/contrib/rails/middleware_spec.rb
+++ b/spec/ddtrace/contrib/rails/middleware_spec.rb
@@ -15,7 +15,7 @@ def index
     end)
   end
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   def all_spans
     tracer.writer.spans(:keep)
diff --git a/spec/ddtrace/contrib/rails/railtie_spec.rb b/spec/ddtrace/contrib/rails/railtie_spec.rb
index 29e0c33f9e7..fe134fec204 100644
--- a/spec/ddtrace/contrib/rails/railtie_spec.rb
+++ b/spec/ddtrace/contrib/rails/railtie_spec.rb
@@ -7,7 +7,7 @@
   before(:each) { skip 'Test not compatible with Rails < 4.0' if Rails.version < '4.0' }
   include_context 'Rails test application'
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   let(:routes) { { '/' => 'test#index' } }
   let(:controllers) { [controller] }
diff --git a/spec/ddtrace/contrib/rake/instrumentation_spec.rb b/spec/ddtrace/contrib/rake/instrumentation_spec.rb
index 5e8568f8d59..14d24f96bb1 100644
--- a/spec/ddtrace/contrib/rake/instrumentation_spec.rb
+++ b/spec/ddtrace/contrib/rake/instrumentation_spec.rb
@@ -1,4 +1,5 @@
 require 'spec_helper'
+require 'ddtrace/contrib/sampling_examples'
 
 require 'securerandom'
 require 'rake'
@@ -7,7 +8,7 @@
 require 'ddtrace/contrib/rake/patcher'
 
 RSpec.describe Datadog::Contrib::Rake::Instrumentation do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:configuration_options) { { tracer: tracer, enabled: true } }
   let(:spans) { tracer.writer.spans }
   let(:span) { spans.first }
@@ -25,10 +26,11 @@
   end
 
   after(:each) do
+    # Reset configuration to defaults
+    Datadog.registry[:rake].reset_configuration!
+
     # We don't want instrumentation enabled during the rest of the test suite...
-    Datadog.configure do |c|
-      c.use :rake, enabled: false
-    end
+    Datadog.configure { |c| c.use :rake, enabled: false }
   end
 
   def reset_task!(task_name)
@@ -87,6 +89,10 @@ def reset_task!(task_name)
           expect(invoke_span.resource).to eq(task_name.to_s)
           expect(invoke_span.parent_id).to eq(0)
         end
+
+        it_behaves_like 'event sample rate' do
+          let(:span) { invoke_span }
+        end
       end
 
       describe '\'rake.execute\' span' do
@@ -94,6 +100,7 @@ def reset_task!(task_name)
           expect(execute_span.name).to eq(Datadog::Contrib::Rake::Ext::SPAN_EXECUTE)
           expect(execute_span.resource).to eq(task_name.to_s)
           expect(execute_span.parent_id).to eq(invoke_span.span_id)
+          expect(execute_span.get_tag(Datadog::Ext::Priority::TAG_EVENT_SAMPLE_RATE)).to be nil
         end
       end
     end
diff --git a/spec/ddtrace/contrib/redis/miniapp_spec.rb b/spec/ddtrace/contrib/redis/miniapp_spec.rb
index 3c77353b521..1e6e9b674f8 100644
--- a/spec/ddtrace/contrib/redis/miniapp_spec.rb
+++ b/spec/ddtrace/contrib/redis/miniapp_spec.rb
@@ -6,7 +6,7 @@
 require 'ddtrace'
 
 RSpec.describe 'Redis mini app test' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   def all_spans
     tracer.writer.spans(:keep)
diff --git a/spec/ddtrace/contrib/redis/redis_spec.rb b/spec/ddtrace/contrib/redis/redis_spec.rb
index 8e4314820d4..accdb9e496c 100644
--- a/spec/ddtrace/contrib/redis/redis_spec.rb
+++ b/spec/ddtrace/contrib/redis/redis_spec.rb
@@ -6,7 +6,7 @@
 require 'ddtrace'
 
 RSpec.describe 'Redis test' do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   def all_spans
     tracer.writer.spans(:keep)
diff --git a/spec/ddtrace/contrib/resque/instrumentation_spec.rb b/spec/ddtrace/contrib/resque/instrumentation_spec.rb
index 67594b55607..70c9768b2a1 100644
--- a/spec/ddtrace/contrib/resque/instrumentation_spec.rb
+++ b/spec/ddtrace/contrib/resque/instrumentation_spec.rb
@@ -1,4 +1,5 @@
 require 'spec_helper'
+require 'ddtrace/contrib/sampling_examples'
 require_relative 'job'
 
 require 'ddtrace'
@@ -6,8 +7,7 @@
 RSpec.describe 'Resque instrumentation' do
   include_context 'Resque job'
 
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
-  let(:pin) { ::Resque.datadog_pin }
+  let(:tracer) { get_test_tracer }
   let(:spans) { tracer.writer.spans }
   let(:span) { spans.first }
 
@@ -15,6 +15,8 @@
   let(:host) { ENV.fetch('TEST_REDIS_HOST', '127.0.0.1') }
   let(:port) { ENV.fetch('TEST_REDIS_PORT', 6379) }
 
+  let(:configuration_options) { { tracer: tracer } }
+
   before(:each) do
     # Setup Resque to use Redis
     ::Resque.redis = url
@@ -22,13 +24,12 @@
 
     # Patch Resque
     Datadog.configure do |c|
-      c.use :resque
+      c.use :resque, configuration_options
     end
-
-    # Update the Resque pin with the tracer
-    pin.tracer = tracer
   end
 
+  after(:each) { Datadog.registry[:resque].reset_configuration! }
+
   shared_examples 'job execution tracing' do
     context 'that succeeds' do
       before(:each) { perform_job(job_class) }
@@ -42,6 +43,8 @@
         expect(span.service).to eq('resque')
         expect(span.status).to_not eq(Datadog::Ext::Errors::STATUS)
       end
+
+      it_behaves_like 'event sample rate'
     end
 
     context 'that fails' do
@@ -71,6 +74,8 @@
         expect(span.status).to eq(Datadog::Ext::Errors::STATUS)
         expect(span.get_tag(Datadog::Ext::Errors::TYPE)).to eq(error_class_name)
       end
+
+      it_behaves_like 'event sample rate'
     end
   end
 
diff --git a/spec/ddtrace/contrib/rest_client/request_patch_spec.rb b/spec/ddtrace/contrib/rest_client/request_patch_spec.rb
index b5a73641d5a..6abaf01a14f 100644
--- a/spec/ddtrace/contrib/rest_client/request_patch_spec.rb
+++ b/spec/ddtrace/contrib/rest_client/request_patch_spec.rb
@@ -5,7 +5,7 @@
 require 'restclient/request'
 
 RSpec.describe Datadog::Contrib::RestClient::RequestPatch do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:rest_client_options) { {} }
 
   before do
diff --git a/spec/ddtrace/contrib/sampling_examples.rb b/spec/ddtrace/contrib/sampling_examples.rb
new file mode 100644
index 00000000000..e8a96e4972a
--- /dev/null
+++ b/spec/ddtrace/contrib/sampling_examples.rb
@@ -0,0 +1,18 @@
+require 'ddtrace/ext/priority'
+
+RSpec.shared_examples_for 'event sample rate' do
+  context 'when not configured' do
+    it 'is not included in the tags' do
+      expect(span.get_metric(Datadog::Ext::Priority::TAG_EVENT_SAMPLE_RATE)).to be nil
+    end
+  end
+
+  context 'when set' do
+    let(:configuration_options) { super().merge(event_sample_rate: event_sample_rate) }
+    let(:event_sample_rate) { 0.5 }
+
+    it 'is included in the tags' do
+      expect(span.get_metric(Datadog::Ext::Priority::TAG_EVENT_SAMPLE_RATE)).to eq(event_sample_rate)
+    end
+  end
+end
diff --git a/spec/ddtrace/contrib/sampling_spec.rb b/spec/ddtrace/contrib/sampling_spec.rb
new file mode 100644
index 00000000000..80d6068c4ce
--- /dev/null
+++ b/spec/ddtrace/contrib/sampling_spec.rb
@@ -0,0 +1,33 @@
+require 'spec_helper'
+
+require 'ddtrace/contrib/sampling'
+
+RSpec.describe Datadog::Contrib::Sampling do
+  describe '::set_event_sample_rate' do
+    subject(:set_event_sample_rate) { described_class.set_event_sample_rate(span, sample_rate) }
+    let(:span) { instance_double(Datadog::Span) }
+
+    context 'when sample rate is nil' do
+      let(:sample_rate) { nil }
+
+      it 'does not set the tag' do
+        expect(span).to_not receive(:set_metric)
+        set_event_sample_rate
+      end
+    end
+
+    context 'when a sample rate is given' do
+      let(:sample_rate) { 0.5 }
+
+      it 'sets the tag' do
+        expect(span).to receive(:set_metric)
+          .with(
+            Datadog::Ext::Priority::TAG_EVENT_SAMPLE_RATE,
+            sample_rate
+          )
+
+        set_event_sample_rate
+      end
+    end
+  end
+end
diff --git a/spec/ddtrace/contrib/sequel/configuration_spec.rb b/spec/ddtrace/contrib/sequel/configuration_spec.rb
index c94f6423c12..de5e5a1dc50 100644
--- a/spec/ddtrace/contrib/sequel/configuration_spec.rb
+++ b/spec/ddtrace/contrib/sequel/configuration_spec.rb
@@ -6,7 +6,7 @@
 require 'ddtrace/contrib/sequel/patcher'
 
 RSpec.describe 'Sequel configuration' do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:spans) { tracer.writer.spans }
   let(:span) { spans.first }
 
diff --git a/spec/ddtrace/contrib/sequel/instrumentation_spec.rb b/spec/ddtrace/contrib/sequel/instrumentation_spec.rb
index fc1c890d110..f1f39dba60f 100644
--- a/spec/ddtrace/contrib/sequel/instrumentation_spec.rb
+++ b/spec/ddtrace/contrib/sequel/instrumentation_spec.rb
@@ -6,7 +6,7 @@
 require 'ddtrace/contrib/sequel/integration'
 
 RSpec.describe 'Sequel instrumentation' do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:configuration_options) { { tracer: tracer } }
   let(:sequel) do
     Sequel.sqlite(':memory:').tap do |s|
diff --git a/spec/ddtrace/contrib/shoryuken/tracer_spec.rb b/spec/ddtrace/contrib/shoryuken/tracer_spec.rb
index 13892002ac3..afa05b21070 100644
--- a/spec/ddtrace/contrib/shoryuken/tracer_spec.rb
+++ b/spec/ddtrace/contrib/shoryuken/tracer_spec.rb
@@ -1,4 +1,6 @@
 require 'spec_helper'
+require 'ddtrace/contrib/sampling_examples'
+
 require 'ddtrace'
 require 'shoryuken'
 
@@ -56,6 +58,12 @@ def perform(sqs_msg, body); end
       expect(span.get_tag(Datadog::Contrib::Shoryuken::Ext::TAG_JOB_ATTRIBUTES)).to eq(attributes.to_s)
     end
 
+    it_behaves_like 'event sample rate' do
+      include_context 'Shoryuken::Worker'
+      let(:body) { {} }
+      before { call }
+    end
+
     context 'with a body' do
       context 'that is a Hash' do
         context 'that contains \'job_class\'' do
@@ -91,6 +99,12 @@ def perform(sqs_msg, body); end
           .and_call_original
       end
 
+      # TODO: These expectations do not work because Shoryuken doesn't run middleware in tests
+      #       https://github.com/phstc/shoryuken/issues/541
+      # it_behaves_like 'event sample rate' do
+      #   before { perform_async }
+      # end
+
       it do
         expect { perform_async }.to_not raise_error
         # TODO: These expectations do not work because Shoryuken doesn't run middleware in tests
diff --git a/spec/ddtrace/contrib/sinatra/activerecord_spec.rb b/spec/ddtrace/contrib/sinatra/activerecord_spec.rb
index 5997ceaba49..0092ed0eb7e 100644
--- a/spec/ddtrace/contrib/sinatra/activerecord_spec.rb
+++ b/spec/ddtrace/contrib/sinatra/activerecord_spec.rb
@@ -11,7 +11,7 @@
 RSpec.describe 'Sinatra instrumentation with ActiveRecord' do
   include Rack::Test::Methods
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:options) { { tracer: tracer } }
 
   let(:span) { spans.first }
diff --git a/spec/ddtrace/contrib/sinatra/multi_app_spec.rb b/spec/ddtrace/contrib/sinatra/multi_app_spec.rb
index 925f070a740..580f7a63966 100644
--- a/spec/ddtrace/contrib/sinatra/multi_app_spec.rb
+++ b/spec/ddtrace/contrib/sinatra/multi_app_spec.rb
@@ -9,7 +9,7 @@
 RSpec.describe 'Sinatra instrumentation for multi-apps' do
   include Rack::Test::Methods
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:options) { { tracer: tracer } }
 
   let(:span) { spans.first }
diff --git a/spec/ddtrace/contrib/sinatra/tracer_spec.rb b/spec/ddtrace/contrib/sinatra/tracer_spec.rb
index 38bb8949620..8bd41ec3b36 100644
--- a/spec/ddtrace/contrib/sinatra/tracer_spec.rb
+++ b/spec/ddtrace/contrib/sinatra/tracer_spec.rb
@@ -9,7 +9,7 @@
 RSpec.describe 'Sinatra instrumentation' do
   include Rack::Test::Methods
 
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
   let(:options) { { tracer: tracer } }
 
   let(:span) { spans.first }
@@ -386,7 +386,7 @@
     include_context 'app with simple route'
 
     subject(:response) { get '/' }
-    let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new, enabled: false) }
+    let(:tracer) { get_test_tracer(enabled: false) }
 
     it do
       is_expected.to be_ok
diff --git a/spec/ddtrace/correlation_spec.rb b/spec/ddtrace/correlation_spec.rb
new file mode 100644
index 00000000000..de2fbe7cb6a
--- /dev/null
+++ b/spec/ddtrace/correlation_spec.rb
@@ -0,0 +1,41 @@
+require 'spec_helper'
+
+require 'ddtrace/correlation'
+require 'ddtrace/context'
+
+RSpec.describe Datadog::Correlation do
+  describe '::identifier_from_context' do
+    subject(:correlation_ids) { described_class.identifier_from_context(context) }
+
+    context 'given nil' do
+      let(:context) { nil }
+
+      it 'returns an empty Correlation::Identifier' do
+        is_expected.to be_a_kind_of(Datadog::Correlation::Identifier)
+        expect(correlation_ids.trace_id).to be 0
+        expect(correlation_ids.span_id).to be 0
+        expect(correlation_ids.to_s).to eq('dd.trace_id=0 dd.span_id=0')
+      end
+    end
+
+    context 'given a Context object' do
+      let(:context) do
+        instance_double(
+          Datadog::Context,
+          trace_id: trace_id,
+          span_id: span_id
+        )
+      end
+
+      let(:trace_id) { double('trace id') }
+      let(:span_id) { double('span id') }
+
+      it 'returns a Correlation::Identifier matching the Context' do
+        is_expected.to be_a_kind_of(Datadog::Correlation::Identifier)
+        expect(correlation_ids.trace_id).to eq(trace_id)
+        expect(correlation_ids.span_id).to eq(span_id)
+        expect(correlation_ids.to_s).to eq("dd.trace_id=#{trace_id} dd.span_id=#{span_id}")
+      end
+    end
+  end
+end
diff --git a/spec/ddtrace/integration_spec.rb b/spec/ddtrace/integration_spec.rb
index 901e874126d..750c0a1cb0d 100644
--- a/spec/ddtrace/integration_spec.rb
+++ b/spec/ddtrace/integration_spec.rb
@@ -148,14 +148,8 @@ def agent_receives_span_step3(previous_success)
   end
 
   describe 'sampling priority metrics' do
-    let(:tracer) do
-      get_test_tracer.tap do |t|
-        t.configure(priority_sampling: true)
-        t.writer = writer
-      end
-    end
-
-    let(:writer) { FauxWriter.new(priority_sampler: Datadog::PrioritySampler.new) }
+    # Sampling priority is enabled by default
+    let(:tracer) { get_test_tracer }
 
     context 'when #sampling_priority is set on a child span' do
       let(:parent_span) { tracer.start_span('parent span') }
@@ -168,7 +162,7 @@ def agent_receives_span_step3(previous_success)
           end.finish
         end.finish
 
-        try_wait_until { writer.spans(:keep).any? }
+        try_wait_until { tracer.writer.spans(:keep).any? }
       end
 
       it do
diff --git a/spec/ddtrace/pin_spec.rb b/spec/ddtrace/pin_spec.rb
index c6d1d80182a..41cbb08e621 100644
--- a/spec/ddtrace/pin_spec.rb
+++ b/spec/ddtrace/pin_spec.rb
@@ -23,7 +23,7 @@
 
     context 'when given sufficient info' do
       let(:options) { { app: 'test-app', app_type: 'test-type', tracer: tracer } }
-      let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+      let(:tracer) { get_test_tracer }
 
       it 'sets the service info' do
         expect(tracer.services.key?(service_name)).to be true
@@ -35,7 +35,7 @@
 
     context 'when given insufficient info' do
       let(:options) { { app_type: 'test-type', tracer: tracer } }
-      let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+      let(:tracer) { get_test_tracer }
 
       it 'does not sets the service info' do
         expect(tracer.services).to be_empty
diff --git a/spec/ddtrace/propagation/http_propagator_spec.rb b/spec/ddtrace/propagation/http_propagator_spec.rb
index 1bbf84db715..5a868ddc782 100644
--- a/spec/ddtrace/propagation/http_propagator_spec.rb
+++ b/spec/ddtrace/propagation/http_propagator_spec.rb
@@ -4,7 +4,7 @@
 require 'ddtrace/propagation/http_propagator'
 
 RSpec.describe Datadog::HTTPPropagator do
-  let(:tracer) { ::Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   describe '#inject!' do
     let(:env) { { 'something' => 'alien' } }
diff --git a/spec/ddtrace/propagation/propagation_integration_spec.rb b/spec/ddtrace/propagation/propagation_integration_spec.rb
index 51197163e8e..72c7384d44d 100644
--- a/spec/ddtrace/propagation/propagation_integration_spec.rb
+++ b/spec/ddtrace/propagation/propagation_integration_spec.rb
@@ -4,7 +4,7 @@
 require 'ddtrace/propagation/http_propagator'
 
 RSpec.describe 'Context propagation' do
-  let(:tracer) { Datadog::Tracer.new(writer: FauxWriter.new) }
+  let(:tracer) { get_test_tracer }
 
   describe 'when max context size is exceeded' do
     let(:max_size) { 3 }
diff --git a/spec/ddtrace/tracer_spec.rb b/spec/ddtrace/tracer_spec.rb
index fbc377faa9c..541ba129cf8 100644
--- a/spec/ddtrace/tracer_spec.rb
+++ b/spec/ddtrace/tracer_spec.rb
@@ -96,4 +96,33 @@
       is_expected.to be(span)
     end
   end
+
+  describe '#active_correlation' do
+    subject(:active_correlation) { tracer.active_correlation }
+
+    context 'when a trace is active' do
+      let(:span) { @span }
+
+      around(:each) do |example|
+        tracer.trace('test') do |span|
+          @span = span
+          example.run
+        end
+      end
+
+      it 'produces an Datadog::Correlation::Identifier with data' do
+        is_expected.to be_a_kind_of(Datadog::Correlation::Identifier)
+        expect(active_correlation.trace_id).to eq(span.trace_id)
+        expect(active_correlation.span_id).to eq(span.span_id)
+      end
+    end
+
+    context 'when no trace is active' do
+      it 'produces an empty Datadog::Correlation::Identifier' do
+        is_expected.to be_a_kind_of(Datadog::Correlation::Identifier)
+        expect(active_correlation.trace_id).to be 0
+        expect(active_correlation.span_id).to be 0
+      end
+    end
+  end
 end
diff --git a/spec/support/tracer_helpers.rb b/spec/support/tracer_helpers.rb
index 706a22ee4ce..3d87f1606dd 100644
--- a/spec/support/tracer_helpers.rb
+++ b/spec/support/tracer_helpers.rb
@@ -4,8 +4,39 @@
 
 module TracerHelpers
   # Return a test tracer instance with a faux writer.
-  def get_test_tracer
-    Datadog::Tracer.new(writer: FauxWriter.new)
+  def get_test_tracer(options = {})
+    options = { writer: FauxWriter.new }.merge(options)
+    Datadog::Tracer.new(options).tap do |tracer|
+      # TODO: Let's try to get rid of this override, which has too much
+      #       knowledge about the internal workings of the tracer.
+      #       It is done to prevent the activation of priority sampling
+      #       from wiping out the configured test writer, by replacing it.
+      tracer.define_singleton_method(:configure) do |opts = {}|
+        super(opts)
+
+        # Re-configure the tracer with a new test writer
+        # since priority sampling will wipe out the old test writer.
+        unless @writer.is_a?(FauxWriter)
+          @writer = if @sampler.is_a?(Datadog::PrioritySampler)
+                      FauxWriter.new(priority_sampler: @sampler)
+                    else
+                      FauxWriter.new
+                    end
+
+          hostname = opts.fetch(:hostname, nil)
+          port = opts.fetch(:port, nil)
+
+          @writer.transport.hostname = hostname unless hostname.nil?
+          @writer.transport.port = port unless port.nil?
+
+          statsd = opts.fetch(:statsd, nil)
+          unless statsd.nil?
+            @writer.statsd = statsd
+            @writer.transport.statsd = statsd
+          end
+        end
+      end
+    end
   end
 
   # Return some test traces
diff --git a/test/context_flush_test.rb b/test/context_flush_test.rb
index c238ba0b411..80446434786 100644
--- a/test/context_flush_test.rb
+++ b/test/context_flush_test.rb
@@ -346,7 +346,7 @@ def test_tracer_configure
     assert_nil(tracer.context_flush)
 
     # If given a partial_flush option, then uses default context flush.
-    flush_tracer = Datadog::Tracer.new(writer: FauxWriter.new, partial_flush: true)
+    flush_tracer = get_test_tracer(partial_flush: true)
     refute_nil(flush_tracer.context_flush)
 
     # If not configured with any flush options, context flush still doesn't exist.
diff --git a/test/helper.rb b/test/helper.rb
index 3f5fe96dbd1..937432b9e3c 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -35,8 +35,39 @@ class Span
 end
 
 # Return a test tracer instance with a faux writer.
-def get_test_tracer
-  Datadog::Tracer.new(writer: FauxWriter.new)
+def get_test_tracer(options = {})
+  options = { writer: FauxWriter.new }.merge(options)
+  Datadog::Tracer.new(options).tap do |tracer|
+    # TODO: Let's try to get rid of this override, which has too much
+    #       knowledge about the internal workings of the tracer.
+    #       It is done to prevent the activation of priority sampling
+    #       from wiping out the configured test writer, by replacing it.
+    tracer.define_singleton_method(:configure) do |opts = {}|
+      super(opts)
+
+      # Re-configure the tracer with a new test writer
+      # since priority sampling will wipe out the old test writer.
+      unless @writer.is_a?(FauxWriter)
+        @writer = if @sampler.is_a?(Datadog::PrioritySampler)
+                    FauxWriter.new(priority_sampler: @sampler)
+                  else
+                    FauxWriter.new
+                  end
+
+        hostname = opts.fetch(:hostname, nil)
+        port = opts.fetch(:port, nil)
+
+        @writer.transport.hostname = hostname unless hostname.nil?
+        @writer.transport.port = port unless port.nil?
+
+        statsd = opts.fetch(:statsd, nil)
+        unless statsd.nil?
+          @writer.statsd = statsd
+          @writer.transport.statsd = statsd
+        end
+      end
+    end
+  end
 end
 
 # Return some test traces
diff --git a/test/sampler_test.rb b/test/sampler_test.rb
index 84a62974db6..624918674b3 100644
--- a/test/sampler_test.rb
+++ b/test/sampler_test.rb
@@ -79,7 +79,7 @@ def test_tracer_with_rate_sampler
     prng = Random.new(123)
 
     tracer = get_test_tracer()
-    tracer.configure(sampler: Datadog::RateSampler.new(0.5))
+    tracer.configure(sampler: Datadog::RateSampler.new(0.5), priority_sampling: false)
 
     nb_spans = 10000
     nb_spans.times do
@@ -87,7 +87,7 @@ def test_tracer_with_rate_sampler
       span.finish()
     end
 
-    spans = tracer.writer.spans()
+    spans = tracer.writer.spans
     expected = nb_spans * 0.5
     assert_in_delta(spans.length, expected, 0.1 * expected)