[tailsamplingprocessor] Support external decision cache implementatio…

…ns (open-telemetry#37035)

#### Description

Adding a feature. This PR adds support for external implementations of
the decision cache. This allows the collector (or another service using
the processor) to supply an alternative decision cache based on
alternative algorithms or external services like memcached without
needing to explicitly add support for all possible options in the
processor.

It re-uses the existing function option pattern and only exposes two
options for now: `WithSampledDecisionCache` and
`WithNonSampledDecisionCache`. I've avoided exporting other options to
avoid bloating the external interface without a concrete use case. The
majority of changes are cleanup from the refactoring to move `Option`
values into the `Config` struct instead of in a variadic parameter on
`newTracesProcessor`.

---------

Co-authored-by: Yuna Verheyden <[email protected]>

.chloggen/tsp-external-cache.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: tailsamplingprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add support for external caches when using the Tailsampling Processor in code.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [37035]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

cmd/checkapi/allowlist.txt

@@ -1,2 +1,3 @@
 extension/observer
 extension/opampcustommessages
+processor/tailsamplingprocessor

processor/tailsamplingprocessor/internal/cache/lru_cache.go → processor/tailsamplingprocessor/cache/lru_cache.go

@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package cache // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/cache"
+package cache // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/cache"
 
 import (
 	"encoding/binary"

processor/tailsamplingprocessor/internal/cache/nop_cache.go → processor/tailsamplingprocessor/cache/nop_cache.go

@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package cache // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/cache"
+package cache // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/cache"
 
 import "go.opentelemetry.io/collector/pdata/pcommon"
 

processor/tailsamplingprocessor/internal/cache/types.go → processor/tailsamplingprocessor/cache/types.go

@@ -1,7 +1,7 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-package cache // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/cache"
+package cache // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/cache"
 
 import "go.opentelemetry.io/collector/pdata/pcommon"
 

processor/tailsamplingprocessor/config.go

@@ -253,4 +253,6 @@ type Config struct {
 	PolicyCfgs []PolicyCfg `mapstructure:"policies"`
 	// DecisionCache holds configuration for the decision cache(s)
 	DecisionCache DecisionCacheConfig `mapstructure:"decision_cache"`
+	// Options allows for additional configuration of the tail-based sampling processor in code.
+	Options []Option `mapstructure:"-"`
 }

processor/tailsamplingprocessor/processor.go

@@ -22,7 +22,7 @@ import (
 	"go.uber.org/zap"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal/timeutils"
-	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/cache"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/cache"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/idbatcher"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/metadata"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/sampling"
@@ -88,7 +88,7 @@ type Option func(*tailSamplingSpanProcessor)
 
 // newTracesProcessor returns a processor.TracesProcessor that will perform tail sampling according to the given
 // configuration.
-func newTracesProcessor(ctx context.Context, set processor.Settings, nextConsumer consumer.Traces, cfg Config, opts ...Option) (processor.Traces, error) {
+func newTracesProcessor(ctx context.Context, set processor.Settings, nextConsumer consumer.Traces, cfg Config) (processor.Traces, error) {
 	telemetrySettings := set.TelemetrySettings
 	telemetry, err := metadata.NewTelemetryBuilder(telemetrySettings)
 	if err != nil {
@@ -124,7 +124,7 @@ func newTracesProcessor(ctx context.Context, set processor.Settings, nextConsume
 	}
 	tsp.policyTicker = &timeutils.PolicyTicker{OnTickFunc: tsp.samplingPolicyOnTick}
 
-	for _, opt := range opts {
+	for _, opt := range cfg.Options {
 		opt(tsp)
 	}
 
@@ -174,15 +174,15 @@ func withTickerFrequency(frequency time.Duration) Option {
 	}
 }
 
-// withSampledDecisionCache sets the cache which the processor uses to store recently sampled trace IDs.
-func withSampledDecisionCache(c cache.Cache[bool]) Option {
+// WithSampledDecisionCache sets the cache which the processor uses to store recently sampled trace IDs.
+func WithSampledDecisionCache(c cache.Cache[bool]) Option {
 	return func(tsp *tailSamplingSpanProcessor) {
 		tsp.sampledIDCache = c
 	}
 }
 
-// withSampledDecisionCache sets the cache which the processor uses to store recently sampled trace IDs.
-func withNonSampledDecisionCache(c cache.Cache[bool]) Option {
+// WithNonSampledDecisionCache sets the cache which the processor uses to store recently non-sampled trace IDs.
+func WithNonSampledDecisionCache(c cache.Cache[bool]) Option {
 	return func(tsp *tailSamplingSpanProcessor) {
 		tsp.nonSampledIDCache = c
 	}

processor/tailsamplingprocessor/processor_decisions_test.go

@@ -15,15 +15,11 @@ import (
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/metric"
 
-	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/cache"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/cache"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/tailsamplingprocessor/internal/sampling"
 )
 
 func TestSamplingPolicyTypicalPath(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -33,7 +29,15 @@ func TestSamplingPolicyTypicalPath(t *testing.T) {
 		{name: "mock-policy-1", evaluator: mpe1, attribute: metric.WithAttributes(attribute.String("policy", "mock-policy-1"))},
 	}
 
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies))
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -63,10 +67,6 @@ func TestSamplingPolicyTypicalPath(t *testing.T) {
 }
 
 func TestSamplingPolicyInvertSampled(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -76,7 +76,15 @@ func TestSamplingPolicyInvertSampled(t *testing.T) {
 		{name: "mock-policy-1", evaluator: mpe1, attribute: metric.WithAttributes(attribute.String("policy", "mock-policy-1"))},
 	}
 
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies))
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -106,10 +114,6 @@ func TestSamplingPolicyInvertSampled(t *testing.T) {
 }
 
 func TestSamplingMultiplePolicies(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -121,7 +125,15 @@ func TestSamplingMultiplePolicies(t *testing.T) {
 		{name: "mock-policy-2", evaluator: mpe2, attribute: metric.WithAttributes(attribute.String("policy", "mock-policy-2"))},
 	}
 
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies))
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -155,10 +167,6 @@ func TestSamplingMultiplePolicies(t *testing.T) {
 }
 
 func TestSamplingPolicyDecisionNotSampled(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -168,7 +176,15 @@ func TestSamplingPolicyDecisionNotSampled(t *testing.T) {
 		{name: "mock-policy-1", evaluator: mpe1, attribute: metric.WithAttributes(attribute.String("policy", "mock-policy-1"))},
 	}
 
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies))
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -199,10 +215,6 @@ func TestSamplingPolicyDecisionNotSampled(t *testing.T) {
 }
 
 func TestSamplingPolicyDecisionInvertNotSampled(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -214,7 +226,15 @@ func TestSamplingPolicyDecisionInvertNotSampled(t *testing.T) {
 		{name: "mock-policy-2", evaluator: mpe2, attribute: metric.WithAttributes(attribute.String("policy", "mock-policy-2"))},
 	}
 
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies))
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -248,10 +268,6 @@ func TestSamplingPolicyDecisionInvertNotSampled(t *testing.T) {
 }
 
 func TestLateArrivingSpansAssignedOriginalDecision(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -263,7 +279,15 @@ func TestLateArrivingSpansAssignedOriginalDecision(t *testing.T) {
 		{name: "mock-policy-2", evaluator: mpe2, attribute: metric.WithAttributes(attribute.String("policy", "mock-policy-2"))},
 	}
 
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies))
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -316,10 +340,6 @@ func TestLateArrivingSpansAssignedOriginalDecision(t *testing.T) {
 }
 
 func TestLateArrivingSpanUsesDecisionCache(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait * 10,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -331,7 +351,17 @@ func TestLateArrivingSpanUsesDecisionCache(t *testing.T) {
 	// Use this instead of the default no-op cache
 	c, err := cache.NewLRUDecisionCache[bool](200)
 	require.NoError(t, err)
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies), withSampledDecisionCache(c))
+
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait * 10,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+			WithSampledDecisionCache(c),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))
@@ -387,10 +417,6 @@ func TestLateArrivingSpanUsesDecisionCache(t *testing.T) {
 }
 
 func TestLateSpanUsesNonSampledDecisionCache(t *testing.T) {
-	cfg := Config{
-		DecisionWait: defaultTestDecisionWait * 10,
-		NumTraces:    defaultNumTraces,
-	}
 	nextConsumer := new(consumertest.TracesSink)
 	idb := newSyncIDBatcher()
 
@@ -402,7 +428,17 @@ func TestLateSpanUsesNonSampledDecisionCache(t *testing.T) {
 	// Use this instead of the default no-op cache
 	c, err := cache.NewLRUDecisionCache[bool](200)
 	require.NoError(t, err)
-	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg, withDecisionBatcher(idb), withPolicies(policies), withNonSampledDecisionCache(c))
+
+	cfg := Config{
+		DecisionWait: defaultTestDecisionWait * 10,
+		NumTraces:    defaultNumTraces,
+		Options: []Option{
+			withDecisionBatcher(idb),
+			withPolicies(policies),
+			WithNonSampledDecisionCache(c),
+		},
+	}
+	p, err := newTracesProcessor(context.Background(), processortest.NewNopSettings(), nextConsumer, cfg)
 	require.NoError(t, err)
 
 	require.NoError(t, p.Start(context.Background(), componenttest.NewNopHost()))