Remove the trends evaluation from the dirty memory custom check

It'll be added in a separate PR

Author: mauroservienti

src/ServiceControl.Audit.Persistence.RavenDB/CustomChecks/CheckDirtyMemory.cs

@@ -1,15 +1,13 @@
 namespace ServiceControl.Audit.Persistence.RavenDB.CustomChecks;
 
 using System;
-using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using NServiceBus.CustomChecks;
 using NServiceBus.Logging;
 
 class CheckDirtyMemory(MemoryInformationRetriever memoryInformationRetriever) : CustomCheck("RavenDB dirty memory trends", "ServiceControl.Audit Health", TimeSpan.FromMinutes(5))
 {
-    readonly List<int> lastDirtyMemoryReads = [];
     public override async Task<CheckResult> PerformCheck(CancellationToken cancellationToken = default)
     {
         var (isHighDirty, dirtyMemoryKb) = await memoryInformationRetriever.GetMemoryInformation(cancellationToken);
@@ -23,83 +21,8 @@ public override async Task<CheckResult> PerformCheck(CancellationToken cancellat
             return CheckResult.Failed(message);
         }
 
-        lastDirtyMemoryReads.Add(dirtyMemoryKb);
-        if (lastDirtyMemoryReads.Count > 20)
-        {
-            //cap the list at 20 which means we're keeping about 1 hour and 40 minutes of data
-            lastDirtyMemoryReads.RemoveAt(0);
-        }
-
-        switch (lastDirtyMemoryReads.Count)
-        {
-            case < 3:
-                Log.Debug("Not enough RavenDB dirty memory data in the series to calculate a trend.");
-                break;
-            // TODO do we need a threshold below which the check never fails?
-            // Three means we'll be observing for 15 minutes before calculating the trend
-            case >= 3 when AnalyzeTrendUsingRegression(lastDirtyMemoryReads) == TrendDirection.Increasing:
-                {
-                    var message = $"RavenDB dirty memory is increasing. Last available value is {dirtyMemoryKb}kb. " +
-                                  $"Check the ServiceControl troubleshooting guide for guidance on how to mitigate the issue. " +
-                                  $"Visit the https://docs.particular.net/servicecontrol/troubleshooting page for more information.";
-                    Log.Warn(message);
-                    return CheckResult.Failed(message);
-                }
-
-            default:
-                // NOP
-                break;
-        }
-
         return CheckResult.Pass;
     }
 
-    static TrendDirection AnalyzeTrendUsingRegression(List<int> values)
-    {
-        if (values is not { Count: > 1 })
-        {
-            throw new ArgumentException("Need at least two values to determine a trend");
-        }
-
-        // Calculate slope using linear regression
-        double numberOfPoints = values.Count;
-        double sumOfIndices = 0;
-        double sumOfValues = 0;
-        double sumOfIndicesMultipliedByValues = 0;
-        double sumOfIndicesSquared = 0;
-
-        for (int i = 0; i < values.Count; i++)
-        {
-            double index = i;
-            double value = values[i];
-
-            sumOfIndices += index;
-            sumOfValues += value;
-            sumOfIndicesMultipliedByValues += index * value;
-            sumOfIndicesSquared += index * index;
-        }
-
-        // Slope formula: (n*Σxy - Σx*Σy) / (n*Σx² - (Σx)²)
-        double slopeNumerator = (numberOfPoints * sumOfIndicesMultipliedByValues) - (sumOfIndices * sumOfValues);
-        double slopeDenominator = (numberOfPoints * sumOfIndicesSquared) - (sumOfIndices * sumOfIndices);
-        double slope = slopeNumerator / slopeDenominator;
-
-        // Determine trend based on slope
-        const double slopeThreshold = 0.001; // Small threshold to handle floating-point precision
-        if (Math.Abs(slope) < slopeThreshold)
-        {
-            return TrendDirection.Flat;
-        }
-
-        return slope > 0 ? TrendDirection.Increasing : TrendDirection.Decreasing;
-    }
-
-    enum TrendDirection
-    {
-        Increasing,
-        Decreasing,
-        Flat
-    }
-
     static readonly ILog Log = LogManager.GetLogger<CheckDirtyMemory>();
 }

src/ServiceControl.Persistence.RavenDB/CustomChecks/CheckDirtyMemory.cs

@@ -1,15 +1,13 @@
 namespace ServiceControl.Persistence.RavenDB.CustomChecks;
 
 using System;
-using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
 using NServiceBus.CustomChecks;
 using NServiceBus.Logging;
 
 class CheckDirtyMemory(MemoryInformationRetriever memoryInformationRetriever) : CustomCheck("RavenDB dirty memory trends", "ServiceControl Health", TimeSpan.FromMinutes(5))
 {
-    readonly List<int> lastDirtyMemoryReads = [];
     public override async Task<CheckResult> PerformCheck(CancellationToken cancellationToken = default)
     {
         var (isHighDirty, dirtyMemoryKb) = await memoryInformationRetriever.GetMemoryInformation(cancellationToken);
@@ -23,83 +21,8 @@ public override async Task<CheckResult> PerformCheck(CancellationToken cancellat
             return CheckResult.Failed(message);
         }
 
-        lastDirtyMemoryReads.Add(dirtyMemoryKb);
-        if (lastDirtyMemoryReads.Count > 20)
-        {
-            //cap the list at 20 which means we're keeping about 1 hour and 40 minutes of data
-            lastDirtyMemoryReads.RemoveAt(0);
-        }
-
-        switch (lastDirtyMemoryReads.Count)
-        {
-            case < 3:
-                Log.Debug("Not enough RavenDB dirty memory data in the series to calculate a trend.");
-                break;
-            // TODO do we need a threshold below which the check never fails?
-            // Three means we'll be observing for 15 minutes before calculating the trend
-            case >= 3 when AnalyzeTrendUsingRegression(lastDirtyMemoryReads) == TrendDirection.Increasing:
-                {
-                    var message = $"RavenDB dirty memory is increasing. Last available value is {dirtyMemoryKb}kb. " +
-                                  $"Check the ServiceControl troubleshooting guide for guidance on how to mitigate the issue. " +
-                                  $"Visit the https://docs.particular.net/servicecontrol/troubleshooting page for more information.";
-                    Log.Warn(message);
-                    return CheckResult.Failed(message);
-                }
-
-            default:
-                // NOP
-                break;
-        }
-
         return CheckResult.Pass;
     }
 
-    static TrendDirection AnalyzeTrendUsingRegression(List<int> values)
-    {
-        if (values is not { Count: > 1 })
-        {
-            throw new ArgumentException("Need at least two values to determine a trend");
-        }
-
-        // Calculate slope using linear regression
-        double numberOfPoints = values.Count;
-        double sumOfIndices = 0;
-        double sumOfValues = 0;
-        double sumOfIndicesMultipliedByValues = 0;
-        double sumOfIndicesSquared = 0;
-
-        for (int i = 0; i < values.Count; i++)
-        {
-            double index = i;
-            double value = values[i];
-
-            sumOfIndices += index;
-            sumOfValues += value;
-            sumOfIndicesMultipliedByValues += index * value;
-            sumOfIndicesSquared += index * index;
-        }
-
-        // Slope formula: (n*Σxy - Σx*Σy) / (n*Σx² - (Σx)²)
-        double slopeNumerator = (numberOfPoints * sumOfIndicesMultipliedByValues) - (sumOfIndices * sumOfValues);
-        double slopeDenominator = (numberOfPoints * sumOfIndicesSquared) - (sumOfIndices * sumOfIndices);
-        double slope = slopeNumerator / slopeDenominator;
-
-        // Determine trend based on slope
-        const double slopeThreshold = 0.001; // Small threshold to handle floating-point precision
-        if (Math.Abs(slope) < slopeThreshold)
-        {
-            return TrendDirection.Flat;
-        }
-
-        return slope > 0 ? TrendDirection.Increasing : TrendDirection.Decreasing;
-    }
-
-    enum TrendDirection
-    {
-        Increasing,
-        Decreasing,
-        Flat
-    }
-
     static readonly ILog Log = LogManager.GetLogger<CheckDirtyMemory>();
 }