[Query] Adds public backend metrics property to Diagnostics (#4001)

* initial commit

* some pr comments, WIP

* Refactor

* more

* Public constructors and modify accumulators

* accumulator updates and undo test changes

* add test

* PR comments

* bug fix

* ToString() refactor

* contract updates

* test updates

* small fixes

* text fix

* Update accumulators

* fix

* PR comments

* small fix

* Rename BE -> ServerSide

* more renaming

* Update API and tests

* separate public and internal classes

* API update

* change namespace

* Pr comments

* public constructors and bug fix

* API updates

* renaming and test updates

* PR comments

* more PR comments

* PR comments, test additions

* API updates and more tests

* tests and pkrangeid update

* PR comments

* more PR comments

* smol test fix

* PR comments - renaming properties and constructor rehash

* contract update

* seal classes and private fields.

* update indexHitRatio calc

* mocking refactor to abstract classes

* contract updates

* PR comments - Update documentation

Microsoft.Azure.Cosmos/src/Diagnostics/CosmosDiagnostics.cs

@@ -43,6 +43,19 @@ public virtual int GetFailedRequestCount()
             throw new NotImplementedException($"{nameof(CosmosDiagnostics)}.{nameof(GetFailedRequestCount)}");
         }
 
+        /// <summary>
+        /// This represents the backend query metrics for the request.
+        /// </summary>
+        /// <remarks>
+        /// This is only applicable for query operations. For all other operations this will return null.
+        /// </remarks>
+        /// <returns>The accumulated backend metrics for the request.</returns>
+        public virtual ServerSideCumulativeMetrics GetQueryMetrics()
+        {
+            // Default implementation avoids breaking change for users upgrading.
+            throw new NotImplementedException($"{nameof(CosmosDiagnostics)}.{nameof(GetQueryMetrics)}");
+        }
+
         /// <summary>
         /// Gets the string field <see cref="CosmosDiagnostics"/> instance in the Azure Cosmos DB database service.
         /// </summary>

Microsoft.Azure.Cosmos/src/Diagnostics/CosmosTraceDiagnostics.cs

@@ -9,12 +9,15 @@ namespace Microsoft.Azure.Cosmos.Diagnostics
     using System.Linq;
     using System.Text;
     using Microsoft.Azure.Cosmos.Json;
+    using Microsoft.Azure.Cosmos.Query.Core.Metrics;
     using Microsoft.Azure.Cosmos.Tracing;
     using Microsoft.Azure.Cosmos.Tracing.TraceData;
     using static Microsoft.Azure.Cosmos.Tracing.TraceData.ClientSideRequestStatisticsTraceDatum;
 
     internal sealed class CosmosTraceDiagnostics : CosmosDiagnostics
     {
+        private readonly Lazy<ServerSideCumulativeMetrics> accumulatedMetrics;
+
         public CosmosTraceDiagnostics(ITrace trace)
         {
             if (trace == null)
@@ -30,6 +33,7 @@ public CosmosTraceDiagnostics(ITrace trace)
             }
 
             this.Value = rootTrace;
+            this.accumulatedMetrics = new Lazy<ServerSideCumulativeMetrics>(() => PopulateServerSideCumulativeMetrics(this.Value));
         }
 
         public ITrace Value { get; }
@@ -49,6 +53,11 @@ public override TimeSpan GetClientElapsedTime()
             return this.Value?.Summary?.RegionsContacted;
         }
 
+        public override ServerSideCumulativeMetrics GetQueryMetrics()
+        {
+            return this.accumulatedMetrics.Value;
+        }
+
         internal bool IsGoneExceptionHit()
         {
             return this.WalkTraceTreeForGoneException(this.Value);
@@ -61,9 +70,9 @@ private bool WalkTraceTreeForGoneException(ITrace currentTrace)
                 return false;
             }
 
-            foreach (object datums in currentTrace.Data.Values)
+            foreach (object datum in currentTrace.Data.Values)
             {
-                if (datums is ClientSideRequestStatisticsTraceDatum clientSideRequestStatisticsTraceDatum)
+                if (datum is ClientSideRequestStatisticsTraceDatum clientSideRequestStatisticsTraceDatum)
                 {
                     foreach (StoreResponseStatistics responseStatistics in clientSideRequestStatisticsTraceDatum.StoreResponseStatisticsList)
                     {
@@ -99,6 +108,17 @@ private ReadOnlyMemory<byte> WriteTraceToJsonWriter(JsonSerializationFormat json
             return jsonTextWriter.GetResult();
         }
 
+        private static ServerSideCumulativeMetrics PopulateServerSideCumulativeMetrics(ITrace trace)
+        {
+            ServerSideMetricsInternalAccumulator accumulator = new ServerSideMetricsInternalAccumulator();
+            ServerSideMetricsInternalAccumulator.WalkTraceTreeForQueryMetrics(trace, accumulator);
+
+            IReadOnlyList<ServerSidePartitionedMetricsInternal> serverSideMetricsList = accumulator.GetPartitionedServerSideMetrics().Select(metrics => new ServerSidePartitionedMetricsInternal(metrics)).ToList();
+
+            ServerSideCumulativeMetrics accumulatedMetrics = new ServerSideCumulativeMetricsInternal(serverSideMetricsList);
+            return accumulatedMetrics.PartitionedMetrics.Count != 0 ? accumulatedMetrics : null;
+        }
+
         public override DateTime? GetStartTimeUtc()
         {
             if (this.Value == null || this.Value.StartTime == null)

Microsoft.Azure.Cosmos/src/Query/Core/Metrics/ClientSideMetrics.cs

@@ -5,7 +5,6 @@ namespace Microsoft.Azure.Cosmos.Query.Core.Metrics
 {
     using System;
     using System.Collections.Generic;
-    using System.Linq;
 
     /// <summary>
     /// Stores client side QueryMetrics.
@@ -54,42 +53,5 @@ public ClientSideMetrics(
         /// Gets the Fetch Execution Ranges for this continuation of the query.
         /// </summary>
         public IEnumerable<FetchExecutionRange> FetchExecutionRanges { get; }
-
-        public ref struct Accumulator
-        {
-            public Accumulator(long retries, double requestCharge, IEnumerable<FetchExecutionRange> fetchExecutionRanges)
-            {
-                this.Retries = retries;
-                this.RequestCharge = requestCharge;
-                this.FetchExecutionRanges = fetchExecutionRanges;
-            }
-
-            public long Retries { get; }
-
-            public double RequestCharge { get; }
-
-            public IEnumerable<FetchExecutionRange> FetchExecutionRanges { get; }
-
-            public Accumulator Accumulate(ClientSideMetrics clientSideMetrics)
-            {
-                if (clientSideMetrics == null)
-                {
-                    throw new ArgumentNullException(nameof(clientSideMetrics));
-                }
-
-                return new Accumulator(
-                    retries: this.Retries + clientSideMetrics.Retries,
-                    requestCharge: this.RequestCharge + clientSideMetrics.RequestCharge,
-                    fetchExecutionRanges: (this.FetchExecutionRanges ?? Enumerable.Empty<FetchExecutionRange>()).Concat(clientSideMetrics.FetchExecutionRanges));
-            }
-
-            public static ClientSideMetrics ToClientSideMetrics(Accumulator accumulator)
-            {
-                return new ClientSideMetrics(
-                    retries: accumulator.Retries,
-                    requestCharge: accumulator.RequestCharge,
-                    fetchExecutionRanges: accumulator.FetchExecutionRanges);
-            }
-        }
     }
 }