Use Singleton Metrics Provider for Listener (#285)

* initial commit

* update version

* add nullable makr

* udpate test

* remove back to v1.5.1

* Fix typo in CHANGELOG.md entry

* Update Directory.Packages.props

* update scalemonitor and target scaler per functionid

* update comments

* update by comments:

* add query metrics throttle

* refactor code a little bit:

CHANGELOG.md

@@ -1,9 +1,10 @@
 # Changelog
 
-## v1.5.1 (Unreleased)
+## v1.5.1
 
 ### Updates
 
+* Use Singelton metrics provider instead of IScaleMonitor and ITargetScaler ([#285]https://github.com/microsoft/durabletask-mssql/pull/285)
 * Updated repo to use central package management
 * Resolved multiple CVEs in dependencies
 

src/DurableTask.SqlServer.AzureFunctions/SqlDurabilityProvider.cs

@@ -22,10 +22,7 @@ class SqlDurabilityProvider : DurabilityProvider
         readonly SqlDurabilityOptions durabilityOptions;
         readonly SqlOrchestrationService service;
 
-        SqlScaleMonitor? scaleMonitor;
-#if FUNCTIONS_V4
-        SqlTargetScaler? targetScaler;
-#endif
+        SqlMetricsProvider? singletonSqlMetricsProvider;
 
         public SqlDurabilityProvider(
             SqlOrchestrationService service,
@@ -200,13 +197,12 @@ public override bool TryGetScaleMonitor(
             string storageConnectionString,
             out IScaleMonitor scaleMonitor)
         {
-            if (this.scaleMonitor == null)
+            if (this.singletonSqlMetricsProvider == null)
             {
-                var sqlMetricsProvider = new SqlMetricsProvider(this.service);
-                this.scaleMonitor = new SqlScaleMonitor(hubName, sqlMetricsProvider);
+                this.singletonSqlMetricsProvider = new SqlMetricsProvider(this.service);
             }
-
-            scaleMonitor = this.scaleMonitor;
+            scaleMonitor = new SqlScaleMonitor(functionId, hubName, this.singletonSqlMetricsProvider);
+
             return true;
         }
 
@@ -218,13 +214,12 @@ public override bool TryGetTargetScaler(
             string connectionName,
             out ITargetScaler targetScaler)
         {
-            if (this.targetScaler == null)
+            if (this.singletonSqlMetricsProvider == null)
             {
-                var sqlMetricsProvider = new SqlMetricsProvider(this.service);
-                this.targetScaler = new SqlTargetScaler(hubName, sqlMetricsProvider);
+                this.singletonSqlMetricsProvider = new SqlMetricsProvider(this.service);
             }
 
-            targetScaler = this.targetScaler;
+            targetScaler = new SqlTargetScaler(functionId, this.singletonSqlMetricsProvider);
             return true;
         }
 #endif

src/DurableTask.SqlServer.AzureFunctions/SqlMetricsProvider.cs

@@ -3,12 +3,15 @@
 
 namespace DurableTask.SqlServer.AzureFunctions
 {
+    using System;
     using System.Threading;
     using System.Threading.Tasks;
 
     public class SqlMetricsProvider
     {
         readonly SqlOrchestrationService service;
+        DateTime metricsTimeStamp = DateTime.MinValue;
+        SqlScaleMetric? metrics;
 
         public SqlMetricsProvider(SqlOrchestrationService service)
         {
@@ -17,13 +20,20 @@ public SqlMetricsProvider(SqlOrchestrationService service)
 
         public virtual async Task<SqlScaleMetric> GetMetricsAsync(int? previousWorkerCount = null)
         {
-            // GetRecommendedReplicaCountAsync will write a trace if the recommendation results
-            // in a worker count that is different from the worker count we pass in as an argument.
-            int recommendedReplicaCount = await this.service.GetRecommendedReplicaCountAsync(
-                previousWorkerCount,
-                CancellationToken.None);
+            // We only want to query the metrics every 5 seconds.
+            if (this.metrics == null || DateTime.UtcNow >= this.metricsTimeStamp.AddSeconds(5))
+            {
+                // GetRecommendedReplicaCountAsync will write a trace if the recommendation results
+                // in a worker count that is different from the worker count we pass in as an argument.
+                int recommendedReplicaCount = await this.service.GetRecommendedReplicaCountAsync(
+                    previousWorkerCount,
+                    CancellationToken.None);
 
-            return new SqlScaleMetric { RecommendedReplicaCount = recommendedReplicaCount };
+                this.metricsTimeStamp = DateTime.UtcNow;
+                this.metrics = new SqlScaleMetric { RecommendedReplicaCount = recommendedReplicaCount };
+            }
+
+            return this.metrics;
         }
     }
 }

src/DurableTask.SqlServer.AzureFunctions/SqlScaleMonitor.cs

@@ -23,14 +23,13 @@ class SqlScaleMonitor : IScaleMonitor<SqlScaleMetric>
 
         int? previousWorkerCount = -1;
 
-        public SqlScaleMonitor(string taskHubName, SqlMetricsProvider sqlMetricsProvider)
+        public SqlScaleMonitor(string functionId, string taskHubName, SqlMetricsProvider sqlMetricsProvider)
         {
-            // Scalers in Durable Functions are shared for all functions in the same task hub.
-            // So instead of using a function ID, we use the task hub name as the basis for the descriptor ID.
-            string id = $"DurableTask-SqlServer:{taskHubName ?? "default"}";
+            // Scalers in Durable Functions is per function ids. And scalers share the same sqlMetricsProvider in the same taskhub. 
+            string id = $"{functionId}-DurableTask-SqlServer:{taskHubName ?? "default"}";
 
 #if FUNCTIONS_V4
-            this.Descriptor = new ScaleMonitorDescriptor(id: id, functionId: id);
+            this.Descriptor = new ScaleMonitorDescriptor(id: id, functionId: functionId);
 #else
             this.Descriptor = new ScaleMonitorDescriptor(id);
 #endif

src/DurableTask.SqlServer.AzureFunctions/SqlTargetScaler.cs

@@ -12,14 +12,12 @@ public class SqlTargetScaler : ITargetScaler
     {
         readonly SqlMetricsProvider sqlMetricsProvider;
 
-        public SqlTargetScaler(string taskHubName, SqlMetricsProvider sqlMetricsProvider)
+        public SqlTargetScaler(string functionId, SqlMetricsProvider sqlMetricsProvider)
         {
             this.sqlMetricsProvider = sqlMetricsProvider;
 
-            // Scalers in Durable Functions are shared for all functions in the same task hub.
-            // So instead of using a function ID, we use the task hub name as the basis for the descriptor ID.
-            string id = $"DurableTask-SqlServer:{taskHubName ?? "default"}";
-            this.TargetScalerDescriptor = new TargetScalerDescriptor(id);
+            // Scalers in Durable Functions is per function ids. And scalers share the same sqlMetricsProvider in the same taskhub. 
+            this.TargetScalerDescriptor = new TargetScalerDescriptor(functionId);
         }
 
         public TargetScalerDescriptor TargetScalerDescriptor { get; }