The design pattern described in this section is suitable whenever the required result is a function of a time period that has lapsed between events, for example:
For accumulating time, it is necessary to assign a variable in which time can be accumulated (in seconds) and to implement a function that checks both the conditions and time accumulated since the last update time transpired. This function is then executed for every Event received to the formula.
The following figure depicts the clock handling time accumulation.
The LastUpdateTime variable stores the last time the update was executed, regardless whether the time counter was updated or not. The function holds the condition that determines whether the time should be updated and accumulated. For example, the time should not be considered if it exceeds the timeslot period, the system status was Down, or the incident had a pending status.
Although the situation detailed here often uses the Tools.NetTime() function to calculate durations, there may be cases where using the standard VB function DateDiff() is preferable.
The Tools.NetTime function incurs an overhead of checking the timeslot each time it is used. It is recommended to avoid using NetTime in the data event procedures since these procedures are called for any new incoming event and therefore invoke the NetTime call. If your timeslot is 24/7, it is recommended that you use the DateDiff function to avoid the overhead of checking the timeslot.
Example 1:
The following 'update counters' routine accumulates the total period of time in the PeriodNetTime variable. In AvailabilityTime the routine accumulates the time that the system status was Up, meaning that the system was available.
The Tools object contains the NetTime method, NetTime(beginTime, endTime)0. This method returns the number of seconds between beginTime and endTime that are within the timeslot of the current Metric. Any time between these two variables is part of a timeslot that is excluded, hence, it is very commonly used for duration calculations where a timeslot is used. (For example: for Priority 1 Tickets resolved within four business hours, where even though a ticket was raised at the end of a business day and might not be solved until the next morning, it is still within SLA due to the timeslot hours being excluded.)
Sub UpdateCounters (time)
PeriodNetTime = PeriodNetTime + tools.NetTime (LastUpdateTime, time)
If SystemStatus = UP Then
AvailabilityTime = AvailabilityTime + tools.NetTime (LastUpdateTime, time)
End If
LastUpdateTime = time
End Sub
Example 2:
The following example calculates the application availability by handling Up and Down events of several critical components, as well as the maintenance events of those components. If all components are under maintenance, time is not considered as expected availability time.
The subroutine UpdateCounters advances the time counters when necessary and is executed with every event received to the formula (Raw Data Event/Engine Event). It also updates the expected available time in cases where the time is within the timeslot period and the components are not within a planned downtime period. The formula updates the actual availability time only when it also has a system status of "Up".
DateDiff is a standard VB function that returns the time between two dates, but does not exclude any timeslot information.
'Force variable declaration
Option Explicit
'Global variables
Dim ExpectedAvailabilityTime
Dim ActualAvailabilityTime
Dim LastUpdateTime
Dim AvailabilityIndicators
Dim MonitoredComponents
Dim DowntimeStatuses
'Map objects creation
Set AvailabilityIndicators=CreateObject("SlalomMap.Map")
Set MonitoredComponents=CreateObject("SlalomMap.Map")
Set DowntimeStatuses=CreateObject("SlalomMap.Map")
'After loading and whenever an infrastructure change occurs
Sub OnRegistration(dispatcher)
dispatcher.RegisterByResourceGroup "OnComponentDownEvent","Component Down","Application Components"
dispatcher.RegisterByResourceGroup "OnComponentUpEvent","Component Up","Application Components"
dispatcher.RegisterByResourceGroup "OnMaintenanceStartEvent","Maintenance Start","Application Components"
dispatcher.RegisterByResourceGroup "OnMaintenanceEndEvent","Maintenance End","Application Components"
UpdateCounters Context.RegistrationTime
Dim AllocatedComponents
Set AllocatedComponents = Context.ResourcesOfResourceGroup("Application Components")
'make sure formula is monitoring only relevant and all the relevant resources
UpdateMonitoredComponents AllocatedComponents
End Sub
Sub OnLoad(time)
'When system goes up for the first time - assume availability OK
LastUpdateTime = time
End Sub
Sub OnPeriodStart(time)
'initializing counters to renew periodic calculation
ExpectedAvailabilityTime = 0
ActualAvailabilityTime = 0
End Sub
Sub OnTimeslotEnter(time)
UpdateCounters time
End Sub
Sub OnTimeslotExit(time)
UpdateCounters time
End Sub
Sub OnComponentDownEvent(eventDetails)
UpdateCounters eventDetails.Time
'write availability status of reported-on resource
AvailabilityIndicators(eventDetails.ResourceId) = _
AvailabilityIndicators(eventDetails.ResourceId)+1
End Sub
Sub OnComponentUpEvent(eventDetails)
UpdateCounters eventDetails.Time
'write availability status of reported-on resource
AvailabilityIndicators(eventDetails.ResourceId)= _
AvailabilityIndicators(eventDetails.ResourceId)-1
End Sub
Sub OnMaintenanceStartEvent(eventDetails)
UpdateCounters eventDetails.Time
'write availability status of reported-on resource
DowntimeStatuses(eventDetails.ResourceId)= _
DowntimeStatuses(eventDetails.ResourceId)+1
End Sub
Sub OnMaintenanceEndEvent(eventDetails)
UpdateCounters eventDetails.Time
'write availability status of reported-on resource
DowntimeStatuses(eventDetails.ResourceId)= _
DowntimeStatuses(eventDetails.ResourceId)-1
End Sub
Sub OnPeriodEnd(time,isComplete)
UpdateCounters time
End Sub
Function Result
If ExpectedAvailabilityTime <> 0 Then
Result = 100 * (ActualAvailabilityTime / ExpectedAvailabilityTime)
Else
Result = Null
End If
End Function
Sub UpdateCounters(time)
If Context.IsWithinTimeslot And Not AllComponentsAreInPlannedDowntime Then
'update counter of seconds in period (when availability is expected)
ExpectedAvailabilityTime = ExpectedAvailabilityTime + DateDiff("s",LastUpdateTime,time)
If SystemIsAvailable Then
'update seconds-of-availability counter
ActualAvailabilityTime = ActualAvailabilityTime + DateDiff("s",LastUpdateTime,time)
End If
End If
LastUpdateTime=time
End Sub
Sub UpdateMonitoredComponents(allocatedComponents)
Dim Component
'add to monitored Components map all new Components to be monitored
For Each Component In allocatedComponents
If Not MonitoredComponents.Exist(Component) Then
MonitoredComponents(Component) = Component
AvailabilityIndicators(Component) = 0
DowntimeStatuses(Component) = 0
End If
Next
'remove from monitored Components map all no-longer-relevant Components
For Each Component In MonitoredComponents
If Not allocatedComponents.Exist(Component) Then
MonitoredComponents.Erase Component
AvailabilityIndicators.Erase Component
DowntimeStatuses.Erase Component
End If
Next
End Sub
Function SystemIsAvailable
Dim SystemAvailability
SystemAvailability = True
Dim Component
Dim ComponentAvailability
For Each Component In MonitoredComponents
ComponentAvailability = AvailabilityIndicators(Component) = 0 _
Or DowntimeStatuses(Component) > 0
'system availability is evaluated with availability
SystemAvailability = SystemAvailability And ComponentAvailability
Next
SystemIsAvailable = SystemAvailability
End Function
Function AllComponentsAreInPlannedDowntime
Dim ComponentsInPlannedDowntime
ComponentsInPlannedDowntime = 0
Dim Component
For Each Component In MonitoredComponents
If DowntimeStatuses(Component) > 0 Then
ComponentsInPlannedDowntime = ComponentsInPlannedDowntime + 1
End If
Next
If ComponentsInPlannedDowntime = MonitoredComponents.Count Then
AllComponentsAreInPlannedDowntime = True
Else
AllComponentsAreInPlannedDowntime = False
End If
End Function
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