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Resource Running Out

What this alert condition does

Alerts when a signal has a certain amount of time before it is exhausted (reaches a specified minimum value) or full (reaches a specified capacity).

When to use this alert condition

It is common to use a Static Threshold for many types of signals that trend to empty or capacity, such as alerting when memory utilization is 80% or when free disk space is below 10%. The Resource Running Out condition provides a more powerful way of receiving alerts for these types of signals, because it takes into account whether a signal is trending up or down (steadily rising or falling).

Example

You might have a detector that triggers an alert when memory utilization goes above 80%, so you have time to look into the issue before the your app is seriously affected. In fact, reaching 80% might only represent a problem if the value has been trending upward and is on a path to reaching 100%. A better way to monitor this signal would be to use the Resource Running Out alert condition, which alerts you when a signal is trending up or down.

In this case, you might say you want to be notified when the signal is expected to hit 80% in 15 minutes (trigger threshold of .25 hours) and has been in this state for 3 minutes (trigger duration of 3m). This will alert you in advance of the error condition, giving you more time to respond, but won’t send a false alert if the signal simply spikes to 80% and then quickly drops to a safer level.

Basic settings

PARAMETER VALUES USAGE NOTES
Alert when nearing Empty, Capacity Choose Empty for signals assumed to be decreasing, Capacity for signals assumed to be increasing
Minimum value/Capacity Number >= 0 Minimum value represents “empty” for the signal (in case Alert when nearing empty) and has a default value of 0. Capacity represents “full” for the signal (in case Alert when nearing capacity) and has no default value; if the signal is a percent, for example, you might enter 100. *
Trigger Sensitivity Low, Medium, High, Custom Approximately how often alerts will be triggered, where Low can result in fewer alerts being triggered and alerts taking longer to clear (least flappy). Choose Custom to modify the settings that determine triggering and clearing sensitivity (listed below).

* If you have specified a metric unit in the plot configuration panel for the signal, the value you enter for Capacity must match the unit you specified. For example, if you specified bytes, you would have to specify 100000000000 (a hundred billion) to specify 100 gigabytes.

Advanced settings

PARAMETER VALUES USAGE NOTES
Trigger threshold Number > 0 The estimated number of hours remaining before resource reaches the specified capacity. Lower values result in lower sensitivity and potentially fewer alerts.
Trigger duration Percent: Integer between 1 and 100; Time indicator: Integer >= 1, followed by time indicator (s, m, h, d, w), e.g. 30s, 10m, 2h, 5d, 1w The number of times the derived signal (i.e. hours remaining) must meet the trigger threshold, compared to the number of expected datapoints. Higher percentages and/or longer time periods result in lower sensitivity and potentially fewer alerts. For more information about this option, see Using the Duration option.
Clear threshold Number > 0; must be higher than Trigger threshold.

The estimated number of hours remaining before the resource reaches the specified capacity. Lower values result in alerts taking longer to clear.

For example, if the Trigger threshold is 24 and the Clear threshold is 36, the alert will be triggered when the resource is projected to reach capacity in 24 hours; it will clear when the projected length of time before reaching capacity increases to 36 hours.

Clear duration Percent: Integer between 1 and 100; Time indicator: Integer >= 1, followed by time indicator (s, m, h, d, w), e.g. 30s, 10m, 2h, 5d, 1w The number of times the derived signal (i.e. hours remaining) must meet the clear threshold, compared to the number of expected datapoints. Higher percentages and/or longer time periods result in longer times for alerts to clear (i.e. increased confidence that the alert condition is in fact no longer occurring). For more information about this option, see Using the Duration option.
Use Double EWMA Yes, No Yes uses a double exponentially weighted moving average to perform forecasts. No uses linear extrapolation. In general, Yes is recommended as a way to handle trends present at a resolution somewhat coarser than data resolution.

Using the Duration option

The Trigger duration and Clear duration options are used to trigger or clear alerts based on how frequently the condition is satisfied during the specified time window. For this alert, the condition being evaluated concerns the forecasted number of hours left, and the forecast is extrapolated when data is missing. Therefore, in the alert when nearing empty case (for example), a short period of descent followed by a long period of missing data may result in an alert being triggered.

Further reading

PARAMETER(S) REMARK(S)
Trigger duration and Clear duration These parameters should be larger than data resolution (in general by a lot).
Trigger threshold and Trigger duration These parameters are naturally a pair: consider a trigger strategy with 3 rules, such as alert if < 72 hours left for 100% of 4 hours, if < 48 hours for 100% of 2 hours, or if < 24 hours for 100% of 1 hour (with increasingly higher levels of severity).
Signal If the signal often does not change, changes may go undetected (depending on “percent” required in the trigger duration).
Signal The alert condition applies a rate of change transformation, and this can interact poorly with other analytics (especially rolling minimum, mean, maximum transformations).
Signal The transformed signal is “hours left.” This quantity will be negative if the signal goes below the specified minimum value (for Empty) or above the specified capacity (for Capacity). This means you may see negative values for “hours left” in the detector’s chart.