[processor/tailsampling] Added debug logging to sampling decision cac…

…hes (#37038)

#### Description

This pull-request adds debug logging to the sampling decision caches,
making it a little easier to debug decisions.

"Trace ID is in the sampled cache" and "Trace ID is in the non-sampled
cache" with the trace ID as a zap field.

---------

Signed-off-by: Sean Porter <[email protected]>

.chloggen/tailsamplingprocessor-decision-cache-logging.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: Added debug logging to the sampling decision caches.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [37038]
+
+# (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: [user]

processor/tailsamplingprocessor/processor.go

@@ -450,6 +450,7 @@ func (tsp *tailSamplingSpanProcessor) processTraces(resourceSpans ptrace.Resourc
 	for id, spans := range idToSpansAndScope {
 		// If the trace ID is in the sampled cache, short circuit the decision
 		if _, ok := tsp.sampledIDCache.Get(id); ok {
+			tsp.logger.Debug("Trace ID is in the sampled cache", zap.Stringer("id", id))
 			traceTd := ptrace.NewTraces()
 			appendToTraces(traceTd, resourceSpans, spans)
 			tsp.releaseSampledTrace(tsp.ctx, id, traceTd)
@@ -460,6 +461,7 @@ func (tsp *tailSamplingSpanProcessor) processTraces(resourceSpans ptrace.Resourc
 		}
 		// If the trace ID is in the non-sampled cache, short circuit the decision
 		if _, ok := tsp.nonSampledIDCache.Get(id); ok {
+			tsp.logger.Debug("Trace ID is in the non-sampled cache", zap.Stringer("id", id))
 			tsp.telemetry.ProcessorTailSamplingEarlyReleasesFromCacheDecision.
 				Add(tsp.ctx, int64(len(spans)), attrSampledFalse)
 			continue
@@ -553,7 +555,7 @@ func (tsp *tailSamplingSpanProcessor) dropTrace(traceID pcommon.TraceID, deletio
 		tsp.numTracesOnMap.Add(^uint64(0))
 	}
 	if trace == nil {
-		tsp.logger.Debug("Attempt to delete traceID not on table")
+		tsp.logger.Debug("Attempt to delete trace ID not on table", zap.Stringer("id", traceID))
 		return
 	}