How do I solve a connection pool issue? - sql-server

Question

I have recently started encountering Database connection issues with SQL Server on my development machine.
System.InvalidOperationException: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool
How can I monitor the connection pool to figure out what is happening?
Further Info:
I haven't had much luck with this - I'm definitely not leaking connections. Every connection is inside a using statement.
When the problem does occur, I have the Performance Monitor window open and it's not showing anywhere near the limit of the pool (which is 100) - generally around 2 - 5 connections, so I don't think the pool is being exhausted so maybe it's a timeout.
However, I have set the ConnectionTimeout to 0 - which, according to the documentation, means it should wait forever to connect - but I'm not seeing this.
When it does occur, it happens fairly quickly - I'm running under the debugger from VS2010 - starting a new instance of my application - and it might happen within a second or two of starting - in starting up the app there are several queries that happen. The actual SQL Server I'm running against is SQL Express 2008. Maybe I should try running it against SQL Server 2008 and see if I see any different behaviour.
Any other ideas?

Answer 1

Take a look at the ADO.NET Performance Counters related to pooling.
Your described symptom is often an indication that you are leaking connections. Make sure all connections are disposed when you are finished with them, preferably by wrapping in an using statement.

Answer 2

here's some code to try the pool and then failover to unpooled:
use this sub if a problem happens with the pool:
Public Sub OpenConn()
Dim sTempCNString As String = cn.ConnectionString
Try
' add a timeout to the cn string, following http://www.15seconds.com/issue/040830.htm
Dim iTimeOut As Integer = utils_Configuration.Get_ConfigInt("DBConnectTimeout", 0)
If (iTimeOut > 0 And Not cn.ConnectionString.ToLower.Contains("timeout")) Then
Diagnostics.Debug.Print("<><><><><><><> SHORT CONNECT WITH POOLING <><><><><><><><><> ")
cn.ConnectionString += ";Connect Timeout=" & iTimeOut.ToString() & ";"
End If
cn.Open()
IsOperational = True
Catch ex As Exception
Diagnostics.Debug.Print("ERROR IN OPENING, try no pool")
' see http://www.15seconds.com/issue/040830.htm
' turn off pooling
Diagnostics.Debug.Print("<><><><><><><> CONNECT WITHOUT POOLING <><><><><><><><><> ")
Dim sAddOn As String = ";Pooling=false;Connect Timeout=45;"
cn.ConnectionString = sTempCNString & sAddOn
cn.ConnectionString = cn.ConnectionString.Replace(";;", ";")
cn.Open()
End Try
End Sub
Here's some code to monitor the pool:
Option Explicit On
Option Strict On
Imports System.Data.SqlClient
Imports System.Diagnostics
Imports System.Runtime.InteropServices
Imports Microsoft.VisualBasic
' ref: http://msdn2.microsoft.com/en-us/library/ms254503.aspx
Public Class utils_SqlPerfMon
Private PerfCounters(9) As PerformanceCounter
Private connection As SqlConnection
Public sConnectString As String = ""
Public sResult As String = ""
Public Sub New()
sConnectString = Tools.GetMainDBConn().ConnectionString
connection = New SqlConnection(sConnectString)
Exec()
End Sub
Public Sub New(ByVal strC As String)
sConnectString = strC
connection = New SqlConnection(sConnectString)
Exec()
End Sub
Public Sub Exec()
Me.SetUpPerformanceCounters()
Diagnostics.Debug.Print("Available Performance Counters:")
' Create the connections and display the results.
Me.CreateConnectionsAndDisplayResults()
End Sub
Private Sub CreateConnectionsAndDisplayResults()
' List the Performance counters.
WritePerformanceCounters()
Dim connection1 As SqlConnection = New SqlConnection( _
Me.sConnectString)
connection1.Open()
Diagnostics.Debug.Print("Opened the 1st Connection:")
WritePerformanceCounters()
connection1.Close()
Diagnostics.Debug.Print("Closed the 1st Connection:")
WritePerformanceCounters()
Return
End Sub
Private Enum ADO_Net_Performance_Counters
NumberOfActiveConnectionPools
NumberOfReclaimedConnections
HardConnectsPerSecond
HardDisconnectsPerSecond
NumberOfActiveConnectionPoolGroups
NumberOfInactiveConnectionPoolGroups
NumberOfInactiveConnectionPools
NumberOfNonPooledConnections
NumberOfPooledConnections
NumberOfStasisConnections
' The following performance counters are more expensive to track.
' Enable ConnectionPoolPerformanceCounterDetail in your config file.
' SoftConnectsPerSecond
' SoftDisconnectsPerSecond
' NumberOfActiveConnections
' NumberOfFreeConnections
End Enum
Private Sub SetUpPerformanceCounters()
connection.Close()
Me.PerfCounters(9) = New PerformanceCounter()
Dim instanceName As String = GetInstanceName()
Dim apc As Type = GetType(ADO_Net_Performance_Counters)
Dim i As Integer = 0
Dim s As String = ""
For Each s In [Enum].GetNames(apc)
Me.PerfCounters(i) = New PerformanceCounter()
Me.PerfCounters(i).CategoryName = ".NET Data Provider for SqlServer"
Me.PerfCounters(i).CounterName = s
Me.PerfCounters(i).InstanceName = instanceName
i = (i + 1)
Next
End Sub
Private Declare Function GetCurrentProcessId Lib "kernel32.dll" () As Integer
Private Function GetInstanceName() As String
'This works for Winforms apps.
'Dim instanceName As String = _
' System.Reflection.Assembly.GetEntryAssembly.GetName.Name
' Must replace special characters like (, ), #, /, \\
Dim instanceName As String = _
AppDomain.CurrentDomain.FriendlyName.ToString.Replace("(", "[") _
.Replace(")", "]").Replace("#", "_").Replace("/", "_").Replace("\\", "_")
'For ASP.NET applications your instanceName will be your CurrentDomain's
'FriendlyName. Replace the line above that sets the instanceName with this:
'instanceName = AppDomain.CurrentDomain.FriendlyName.ToString.Replace("(", "[") _
' .Replace(")", "]").Replace("#", "_").Replace("/", "_").Replace("\\", "_")
Dim pid As String = GetCurrentProcessId.ToString
instanceName = (instanceName + ("[" & (pid & "]")))
Diagnostics.Debug.Print("Instance Name: {0}", instanceName)
Diagnostics.Debug.Print("---------------------------")
Return instanceName
End Function
Private Sub WritePerformanceCounters()
Dim sdelim As String = vbCrLf ' "<br>"
Diagnostics.Debug.Print("---------------------------")
sResult += "---------------------------"
sResult += sdelim
Dim strTemp As String = ""
For Each p As PerformanceCounter In Me.PerfCounters
Try
Diagnostics.Debug.Print("{0} = {1}", p.CounterName, p.NextValue)
strTemp = p.CounterName & "=" & p.NextValue.ToString
Catch ex As Exception
strTemp = ""
End Try
sResult += strTemp
sResult += sdelim
Next
Diagnostics.Debug.Print("---------------------------")
sResult += "---------------------------"
sResult += sdelim
End Sub
Private Shared Function GetSqlConnectionStringDifferent() As String
' To avoid storing the connection string in your code,
' you can retrive it from a configuration file.
Return ("Initial Catalog=AdventureWorks;Data Source=.\SqlExpress;" & _
"User Id=LowPriv;Password=Data!05;")
End Function
End Class