Why would a database timeout?


when i run queries to the database im constantly getting this

System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
Generated: Tue, 18 Aug 2009 08:05:39 GMT

System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.Data.SqlClient.SqlException: Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.SqlDataReader.ConsumeMetaData()
   at System.Data.SqlClient.SqlDataReader.get_MetaData()
   at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
   at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteDbDataReader(CommandBehavior behavior)
   at System.Data.Common.DbCommand.ExecuteReader()
   at System.Data.Linq.SqlClient.SqlProvider.Execute(Expression query, QueryInfo queryInfo, IObjectReaderFactory factory, Object[] parentArgs, Object[] userArgs, ICompiledSubQuery[] subQueries, Object lastResult)
   at System.Data.Linq.SqlClient.SqlProvider.ExecuteAll(Expression query, QueryInfo[] queryInfos, IObjectReaderFactory factory, Object[] userArguments, ICompiledSubQuery[] subQueries)
   at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
   at System.Data.Linq.DataQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at System.Data.Linq.Provider.BindingList.Create[T](DataContext context, IEnumerable`1 sequence)
   at System.Data.Linq.DataQuery`1.GetNewBindingList()
   at System.Data.Linq.DataQuery`1.System.ComponentModel.IListSource.GetList()
   at System.Windows.Forms.CurrencyManager.SetDataSource(Object dataSource)
   at System.Windows.Forms.BindingContext.EnsureListManager(Object dataSource, String dataMember)
   at System.Windows.Forms.BindingContext.get_Item(Object dataSource)
   at PlexityHide.GTP.TimeItemDataConnect.Wire()
   at PlexityHide.GTP.TimeItemDataConnect.UpdateDataSource(IListSource aDataSource, String aDataMember, Layer aLayer)
   at PlexityHide.GTP.TimeItemDataConnect.set_DataSource(Object value)
   at PlexityHide.GTP.Layer.set_DataSource(Object value)
   at WebSchedule._Default.Grid_OnEachListItemWhenDataBound_GridNode(Object GTPComponent, EachListItemWhenDataBoundArgs e) in C:\MyDev\WebSchedule\Schedule.aspx.cs:line 503
   at PlexityHide.GTP.Grid.NodeChangedInDS(GridNode aNode)
   at PlexityHide.GTP.NodeDataConnect.UpdateRowContent(Int32 index)
   at PlexityHide.GTP.NodeDataConnect.EnsureBindUpToDate()
   at PlexityHide.GTP.GridNodes.get_Count()
   at PlexityHide.GTP.GridStructure.get_FirstVisibleNode()
   at PlexityHide.GTP.Gantt.set_TurnOffAllCollisionDetect(Boolean value)
   at PlexityHide.GTP.WEB.Gantt_ASP.OnPreRender(EventArgs e)
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.BasePartialCachingControl.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   --- End of inner exception stack trace ---
   at System.Web.UI.Page.HandleError(Exception e)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   at System.Web.UI.Page.ProcessRequest()
   at System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context)
   at System.Web.UI.Page.ProcessRequest(HttpContext context)
   at ASP.schedule_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\13c4fe72\f906a8a8\App_Web_schedule.aspx.cdcab7d2.nhap4sin.0.cs:line 0
   at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

could it be caused by the number of connections that are going to the database at anyone time? the page in question calls a gantt chart and populates it with the data from a schedule table per a specific contract. and what is happening is that if say 10 people are making the call to the table at the same time i get the timeout happening


Answers:


It's possible that you've got too many long-running queries. Another very likely cause is that you're not closing the connections as soon as you've finished with them, which releases them to the connection pool.

In general, you should acquire connections as late as possible and release them as early as possible with a using statement, to avoid just this kind of situation. If you don't close the connection explicitly (even in the face of exceptions) you're putting yourself at the mercy of the garbage collector and finalizers to return the connection to the pool.

If you believe you genuinely have many active connections with long-running queries, you should increase the number of connections in the connection pool. If you believe it's the actual query itself timing out (i.e. taking longer than you're allowing) then you should increase the timeout for the command or connection.