How Can I Group Labels in a Prometheus Query?
Grouping labels in a Prometheus query allows you to aggregate metrics based on specific labels, providing a way to analyze data across different dimensions. You can use the by clause in Prometheus Query Language (PromQL) to group your results according to one or more labels. Here’s how to do it effectively.
Basic Syntax for Grouping
The general syntax for grouping in a Prometheus query looks like this:
aggregation_function(metric_name) by (label1, label2, ...)
Step-by-Step Examples
1. Counting Total Requests by Method
Suppose you have a metric called http_requests_total that counts HTTP requests. If you want to count the total number of requests grouped by the method label (e.g., GET, POST), you can use:
sum(http_requests_total) by (method)
This query sums the total requests and groups the result by the method label, giving you the total number of requests for each HTTP method.
2. Average Response Time by Status
If you want to calculate the average response time grouped by the status label, and you have a metric called http_response_time_seconds, you can use:
avg(http_response_time_seconds) by (status)
This returns the average response time for each unique status code.
3. Grouping by Multiple Labels
You can also group by multiple labels. For instance, if you want to count the total requests grouped by both method and status, you can do:
sum(http_requests_total) by (method, status)
This query returns the total number of requests for each combination of HTTP method and status.
Step 4: Using Without and Without Keywords
1. Using without
If you want to aggregate metrics while ignoring certain labels, you can use the without keyword. For example, if you want to sum total requests but ignore the instance label, you can write:
sum(http_requests_total) without (instance)
This aggregates the total requests across all instances.
2. Using on and ignoring
You can also combine groupings using on and ignoring. For example, if you want to group by method but ignore the instance label:
sum(http_requests_total) by (method)
* on(method)
sum(http_response_time_seconds) by (method)
This allows you to perform operations while maintaining focus on the method label.
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