[Sampler.Aws] perf improvements for AWS Xray sampler (open-telemetry#2046)

Author: birojnayak

src/OpenTelemetry.Sampler.AWS/AWSXRayRemoteSampler.cs

@@ -15,6 +15,7 @@ public sealed class AWSXRayRemoteSampler : Trace.Sampler, IDisposable
     internal static readonly TimeSpan DefaultTargetInterval = TimeSpan.FromSeconds(10);
 
     private static readonly Random Random = new Random();
+    private bool isFallBackEventToWriteSwitch = true;
 
     [SuppressMessage("Performance", "CA5394: Do not use insecure randomness", Justification = "Secure random is not required for jitters.")]
     internal AWSXRayRemoteSampler(Resource resource, TimeSpan pollingInterval, string endpoint, Clock clock)
@@ -82,10 +83,18 @@ public override SamplingResult ShouldSample(in SamplingParameters samplingParame
     {
         if (this.RulesCache.Expired())
         {
-            AWSSamplerEventSource.Log.InfoUsingFallbackSampler();
+            if (this.isFallBackEventToWriteSwitch)
+            {
+                this.isFallBackEventToWriteSwitch = false;
+
+                // could be expensive operation, conditionally call once
+                AWSSamplerEventSource.Log.InfoUsingFallbackSampler();
+            }
+
             return this.FallbackSampler.ShouldSample(in samplingParameters);
         }
 
+        this.isFallBackEventToWriteSwitch = true;
         return this.RulesCache.ShouldSample(in samplingParameters);
     }
 

src/OpenTelemetry.Sampler.AWS/CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+## 0.1.0-alpha.2
+
+* Performance problem fix for calling event source when required.
+  ([#2046](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/2046))
+
 ## 0.1.0-alpha.1
 
 Released 2024-Jun-20

src/OpenTelemetry.Sampler.AWS/RulesCache.cs

@@ -11,6 +11,7 @@ internal class RulesCache : IDisposable
     private const int CacheTTL = 60 * 60; // cache expires 1 hour after the refresh (in sec)
 
     private readonly ReaderWriterLockSlim rwLock;
+    private bool isFallBackEventToWriteSwitch = true;
 
     public RulesCache(Clock clock, string clientId, Resource resource, Trace.Sampler fallbackSampler)
     {
@@ -85,13 +86,19 @@ public SamplingResult ShouldSample(in SamplingParameters samplingParameters)
         {
             if (ruleApplier.Matches(samplingParameters, this.Resource))
             {
+                this.isFallBackEventToWriteSwitch = true;
                 return ruleApplier.ShouldSample(in samplingParameters);
             }
         }
 
         // ideally the default rule should have matched.
         // if we are here then likely due to a bug.
-        AWSSamplerEventSource.Log.InfoUsingFallbackSampler();
+        if (this.isFallBackEventToWriteSwitch)
+        {
+            this.isFallBackEventToWriteSwitch = false;
+            AWSSamplerEventSource.Log.InfoUsingFallbackSampler();
+        }
+
         return this.FallbackSampler.ShouldSample(in samplingParameters);
     }