Every alert rule is assigned to an evaluation group. You can assign the alert rule to an existing evaluation group or create a new one.
Each evaluation group contains an **evaluation interval** that determines how frequently the alert rule is checked. For instance, the evaluation may occur every `10s`, `30s`, `1m`, `10m`, etc.
Alert rules in different groups can be evaluated simultaneously.
**Grafana-managed** alert rules within the same group are evaluated simultaneously. However, **data-source managed** alert rules within the same group are evaluated one after the other—this is necessary to ensure that recording rules are evaluated before alert rules.
## Pending period
You can set a pending period to prevent unnecessary alerts from temporary issues.
The pending period specifies how long the condition must be met before firing, ensuring the condition is consistently met over a consecutive period.
You can also set the pending period to zero to skip it and have the alert fire immediately once the condition is met.
## Evaluation example
Keep in mind:
- One alert rule can generate multiple alert instances - one for each time series produced by the alert rule's query.
- Alert instances from the same alert rule may be in different states. For instance, only one observed machine might start firing.
Consider an alert rule with an **evaluation interval** set at every 30 seconds and a **pending period** of 90 seconds. The evaluation occurs as follows:
