feat: Added partial granularity samplers and assign transactions with isPartialTrace when partial granularity sampling decisions have been made

lib/agent.js

@@ -5,7 +5,6 @@
 
 'use strict'
 
-const determineSampler = require('./samplers/determine-sampler')
 const CollectorAPI = require('./collector/api')
 const ServerlessCollector = require('./collector/serverless')
 const DESTINATIONS = require('./config/attribute-filter').DESTINATIONS
@@ -41,6 +40,7 @@ const synthetics = require('./synthetics')
 const Harvester = require('./harvester')
 const { createFeatureUsageMetrics } = require('./util/application-logging')
 const HealthReporter = require('./health-reporter')
+const Samplers = require('./samplers')
 
 // Map of valid states to whether or not data collection is valid
 const STATES = {
@@ -288,15 +288,7 @@ function Agent(config) {
     this.harvester
   )
 
-  // Instantiate sampling decisions.
-  this.sampler = {}
-  // This is the global adaptive sampler instance used across
-  // different sampling modes and not intended to be used directly.
-  this.sampler._globalAdaptiveSampler = null
-  // The samplers to use for a particular sampler mode.
-  this.sampler.root = determineSampler({ agent: this, config, sampler: 'root' })
-  this.sampler.remoteParentSampled = determineSampler({ agent: this, config, sampler: 'remote_parent_sampled' })
-  this.sampler.remoteParentNotSampled = determineSampler({ agent: this, config, sampler: 'remote_parent_not_sampled' })
+  this.samplers = new Samplers(this)
 
   this.queries = new QueryTraceAggregator(
     {
@@ -852,17 +844,10 @@ Agent.prototype._listenForConfigChanges = function _listenForConfigChanges() {
     self.txSegmentNormalizer.load.apply(self.txSegmentNormalizer, arguments)
   })
   this.config.on('sampling_target', function updateSamplingTarget(target) {
-    // Remember config.sampling_target is an alias for
-    // config.distributed_tracing.sampler.adaptive_sampling_target,
-    // which is the sampling target for the global adaptive sampler.
-    if (self.sampler._globalAdaptiveSampler) {
-      self.sampler._globalAdaptiveSampler.samplingTarget = target
-    }
+    self.samplers.updateAdaptiveTarget(target)
   })
   this.config.on('sampling_target_period_in_seconds', function updateSamplePeriod(period) {
-    if (self.sampler._globalAdaptiveSampler) {
-      self.sampler._globalAdaptiveSampler.samplingPeriod = period * 1000
-    }
+    self.samplers.updateAdaptivePeriod(period)
   })
   this.config.on('event_harvest_config', function onHarvestConfigReceived(harvestConfig) {
     if (harvestConfig) {

lib/samplers/README.md

@@ -64,14 +64,15 @@ distributed_tracing:
 
 There are two sampler modes, each with three sampler sections, resulting in potentially six different sampling decisions that the agent would have to support. We create a new `Sampler` instance (`AdaptiveSampler`, `AlwaysOnSampler`, `AlwaysOffSampler`, or `TraceIdRatioBasedSampler`, defined in this folder) for each of these sampler modes' sections.
 
-`agent.sampler` is defined as:
+`agent.samplers` is defined as:
 
-* `agent.sampler.root`
-* `agent.sampler.remoteParentSampled`
-* `agent.sampler.remoteParentNotSampled`
-* `agent.sampler.partialGranularity.root`
-* `agent.sampler.partialGranularity.remoteParentSampled`
-* `agent.sampler.partialGranularity.remoteParentNotSampled`
+* `agent.samplers.root`
+* `agent.samplers.remoteParentSampled`
+* `agent.samplers.remoteParentNotSampled`
+* `agent.samplers.partialRoot`
+* `agent.samplers.partialRemoteParentSampled`
+* `agent.samplers.partialRemoteParentNotSampled`
+* `agent.samplers.adaptiveSampler` (if needed, see below)
 
 These samplers have a `applySamplingDecision({transaction})` function, which `Transaction` calls (in `lib/transaction/index.js`) to update its `sampled` field and therefore its `priority`.
 

lib/samplers/adaptive-sampler.js

@@ -109,8 +109,9 @@ class AdaptiveSampler extends Sampler {
     return false
   }
 
-  applySamplingDecision({ transaction, tracestate = null }) {
+  applySamplingDecision({ transaction, tracestate, isFullTrace }) {
     if (!transaction) return
+    transaction.isPartialTrace = !isFullTrace
     if (tracestate) {
       // Explicitly set sampled and priority from tracestate intrinsics if available
       transaction.sampled = tracestate?.intrinsics ? tracestate.isSampled : null
@@ -122,7 +123,8 @@ class AdaptiveSampler extends Sampler {
     // eslint-disable-next-line sonarjs/pseudo-random
     const initPriority = Math.random()
     transaction.sampled = this.shouldSample(initPriority)
-    transaction.priority = transaction.sampled ? initPriority + 1 : initPriority
+    // only add 1 to priority when doing a full trace
+    transaction.priority = transaction.sampled && isFullTrace ? initPriority + 1 : initPriority
     // Truncate the priority after potentially modifying it to avoid floating
     // point errors.
     transaction.priority = ((transaction.priority * 1e6) | 0) / 1e6

lib/samplers/always-off-sampler.js

@@ -2,12 +2,12 @@
  * Copyright 2025 New Relic Corporation. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  */
-
 const Sampler = require('./sampler')
 
 class AlwaysOffSampler extends Sampler {
-  applySamplingDecision({ transaction }) {
+  applySamplingDecision({ transaction, isFullTrace }) {
     if (!transaction) return
+    transaction.isPartialTrace = !isFullTrace
     transaction.priority = 0
     transaction.sampled = false
   }

lib/samplers/always-on-sampler.js

@@ -6,8 +6,9 @@
 const Sampler = require('./sampler')
 
 class AlwaysOnSampler extends Sampler {
-  applySamplingDecision({ transaction }) {
+  applySamplingDecision({ transaction, isFullTrace }) {
     if (!transaction) return
+    transaction.isPartialTrace = !isFullTrace
     transaction.priority = 2.0
     transaction.sampled = true
   }