PromQL Example Queries
Video Lecture
Description
Now that we have a few scape targets, it is time to delve into queries.
The query language used in Prometheus is called PromQL (Prometheus Query Language).
The data can either be viewed as a graph, as tabled data, or in external systems such as Grafana, Zabbix and others.
Example,
scrape_duration_seconds
This shows multiple time series results. 1 for each target,
we can filter for 1 target by including either the instance, or job labels
scrape_duration_seconds{instance="localhost:9100"}
Regular Expressions
We can also use regular expressions.
Go back to the console view and query for node_cpu_seconds_total
We should get about 8 time series results.
Lets filter for everything with mode containing irq
node_cpu_seconds_total{mode=~".*irq"}
All regular expressions in Prometheus use the RE2 syntax.
Data Types
Scalar
A numeric floating point value. Examples of scalars include -1, 12.34 and 12345678.9
Instant vector
A set of time series containing a single sample for each time series, all sharing the same timestamp
scrape_duration_seconds{instance="localhost:9100"}
Range Vector
A set of time series containing a range of data points over time for each time series.
Return a whole range of scrape_duration_seconds (in this case 5 minutes) for the same vector, making it a range vector.
node_netstat_Tcp_InSegs{instance="localhost:9100"}[5m]
node_netstat_Tcp_InSegs{instance="localhost:9100"}[1m]
node_netstat_Tcp_InSegs{instance="localhost:9100"}[30s]
Press the graph, we get an error saying that expression type "range vector" for range query, must be Scalar or instant Vector
So when in the graph view, remove the [5m] range option.
Functions
rate(scrape_duration_seconds{instance="localhost:9100"}[1m:20s])
Start with
node_netstat_Tcp_InSegs
create a range vector covering 1m
node_netstat_Tcp_InSegs[10m]
filter for the job prometheus
node_netstat_Tcp_InSegs{job="prometheus"}[10m]
calculates the per-second average rate of increase of the time series in the range vector
rate(node_netstat_Tcp_InSegs[10m])
sum the 2 values
sum(go_threads)
Sub Queries
Start with this instant vector
node_netstat_Tcp_InSegs{instance="localhost:9100"}
Convert it to a Range Vector and then convert it back to an instant vector using rate
rate(node_netstat_Tcp_InSegs{instance="localhost:9100"}[1m])
Wrap it in the ceiling function
ceil(rate(node_netstat_Tcp_InSegs{instance="localhost:9100"}[1m]))
Convert it to a range vector and get the per-second derivative of the time series
deriv(ceil(rate(node_netstat_Tcp_InSegs{instance="localhost:9100"}[1m]))[1m:])