Writing prometheus test with metric operations/function

[Belmark Caday]

Here's my stackoverflow question : 

https://stackoverflow.com/questions/60992785/writing-prometheus-test-with-metric-operations-function

anyone can help?

[Brian Candler]

Expression 1 uses a range vector (data over a 1 hour time window) with predict_linear.  However if you only provide one data point, then there's no way it can do linear regression to fit a line.

Expression 2 performs an operation between two different metrics, but you've only provided a data point for one metric.

[Belmark Caday]

On Friday, April 3, 2020 at 3:02:45 PM UTC+8, Brian Candler wrote:

Expression 1 uses a range vector (data over a 1 hour time window) with predict_linear.  However if you only provide one data point, then there's no way it can do linear regression to fit a line.

 

       I already changed the time window to 1m, still it fails the test. can you give me example how to test it? 

[Brian Candler]

Put at least two data points in the time series.

[Belmark Caday]

Here are the udpdated tests : 

 - series: 'node_filesystem_free{fstype="ext4"}'

   values: '1+0x120'

 - expr: 'predict_linear(node_filesystem_free{fstype!~"tmpfs"}[1h], 4 * 3600) > 0'                                                                                                                                    

   eval_time: 1m                                                                                                                                                                                                      

   exp_samples:                                                                                                                                                                                                        

     - labels: 'node_filesystem_free{fstype="ext4"}'                                                                                                                                                                      

       value: 1          

And here is the error message I get: 

  FAILED:

    expr: "predict_linear(node_filesystem_free{fstype!~\"tmpfs\"}[1h], 4 * 3600) > 0", time: 1m0s,

        exp:"{__name__=\"node_filesystem_free\", fstype=\"ext4\"} 1E+00"

        got:"{fstype=\"ext4\"} 1E+00"

[Brian Candler]

Good: the error message tells you exactly what the problem is.  You said the expected result is

node_filesystem_free{fstype="ext4"} 1

but the actual result was

{fstype="ext4"} 1

That is correct: the output of the predict_linear() function is a timeseries with no metric name.

If you go to the prometheus GUI (normally on port 9090) and try these two promQL expressions, you'll see the difference:

node_filesystem_free_bytes{fstype!~"tmpfs"}

predict_linear(node_filesystem_free_bytes{fstype!~"tmpfs"}[1h], 4 * 3600)

HTH,

Brian.