Reduce memory usage by reclaimed MetricPoint (#5416)

src/OpenTelemetry/Metrics/AggregatorStore.cs

@@ -297,9 +297,7 @@ internal void SnapshotDeltaWithMetricPointReclaim()
                 {
                     var lookupData = metricPoint.LookupData;
 
-                    // Setting `LookupData` to `null` to denote that this MetricPoint is reclaimed.
-                    // Snapshot method can use this to skip trying to reclaim indices which have already been reclaimed and added to the queue.
-                    metricPoint.LookupData = null;
+                    metricPoint.Reclaim();
 
                     Debug.Assert(this.TagsToMetricPointIndexDictionaryDelta != null, "this.tagsToMetricPointIndexDictionaryDelta was null");
 

src/OpenTelemetry/Metrics/MetricPoint.cs

@@ -19,11 +19,6 @@ public struct MetricPoint
     // ReferenceCount doesn't matter for MetricPoint with no tags and overflow attribute as they are never reclaimed.
     internal int ReferenceCount;
 
-    // When the AggregatorStore is reclaiming MetricPoints, this serves the purpose of validating the a given thread is using the right
-    // MetricPoint for update by checking it against what as added in the Dictionary. Also, when a thread finds out that the MetricPoint
-    // that its using is already reclaimed, this helps avoid sorting of the tags for adding a new Dictionary entry.
-    internal LookupData? LookupData;
-
     private const int DefaultSimpleReservoirPoolSize = 1;
 
     private readonly AggregatorStore aggregatorStore;
@@ -155,6 +150,12 @@ internal MetricPointStatus MetricPointStatus
         private set;
     }
 
+    // When the AggregatorStore is reclaiming MetricPoints, this serves the purpose of validating the a given thread is using the right
+    // MetricPoint for update by checking it against what as added in the Dictionary. Also, when a thread finds out that the MetricPoint
+    // that its using is already reclaimed, this helps avoid sorting of the tags for adding a new Dictionary entry.
+    // Snapshot method can use this to skip trying to reclaim indices which have already been reclaimed and added to the queue.
+    internal LookupData? LookupData { readonly get; private set; }
+
     internal readonly bool IsInitialized => this.aggregatorStore != null;
 
     /// <summary>
@@ -1195,6 +1196,15 @@ internal void TakeSnapshotWithExemplar(bool outputDelta)
         }
     }
 
+    /// <summary>
+    /// Denote that this MetricPoint is reclaimed.
+    /// </summary>
+    internal void Reclaim()
+    {
+        this.LookupData = null;
+        this.mpComponents = null;
+    }
+
     private void UpdateHistogram(double number, ReadOnlySpan<KeyValuePair<string, object?>> tags = default, bool isSampled = false)
     {
         Debug.Assert(this.mpComponents?.HistogramBuckets != null, "HistogramBuckets was null");