Sitecore Log File Repeated Error

Question

I have a sitecore 7.2 site and it is upgraded from 6.6, Any ideas what cause the following error to be appears many times in log file:

ManagedPoolThread #3 2015:07:14 10:03:48 ERROR Exception occurred in retryer scope :
   at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
   at System.Environment.get_StackTrace()
   at Sitecore.Data.DataProviders.Retryer.ExecuteNoResult(Action action, Action recover)
   at Sitecore.Analytics.Automation.Data.Sql.SqlAutomationProvider.GetDueStates(AutomationStatesDataTable dataTable, Int32 maxEntries)
   at Sitecore.Analytics.Automation.AutomationWorker.GetDueStates(AutomationStatesDataTable dataTable)
   at Sitecore.Analytics.Automation.AutomationWorker.Process()
   at Sitecore.Analytics.Automation.AutomationWorker.<Wakeup>b__4(Object state)
   at Sitecore.Threading.ManagedThreadPool.ProcessQueuedItems()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Answer 1

The reason you see the same error multiple times is because of the retryer which will retry failed database requests a number of times equal to that set in the number of tries param.

Below is the retryer section taken from web.config v7.2:

<!-- RETRYER
         When enabled, the Retryer resends failed database requests a specified number of times.
         For example, this is useful if you configure a Sitecore instance to support hot failover for database calls.
         Default value: disabled="true"
    -->
    <retryer disabled="true" type="Sitecore.Data.DataProviders.Retryer, Sitecore.Kernel">
      <param desc="Number of tries">6</param>
      <param desc="Interval between tries">00:00:00.500</param>
      <param desc="Log each exception (should be used for debug only)">true</param>
    </retryer>