> Can I set a scraping interval of a job to 20 minutes? At the moment, one 
can't adjust query delta look-back per scrape job.

It's not recommended to scrape less frequently than once every 2 minutes.  
With the default 5-minute lookback, this gives a degree of robustness 
against losing a single scrape.

In theory, you could set the lookback to say 50 minutes and then scrape 
every 20 minutes.  Like I say, it's not recommended, and as you've 
observed, this is a global setting.

Is there a particular reason why scraping every 2 minutes can't be done?  
Don't worry about TSDB storage.  Prometheus does delta-compression, so if 
repeated scrapes of the same exporter give the same value, the difference 
between them is zero and it uses hardly any storage at all (just the 
timestamp deltas).

If the problem is that your scrape task is expensive to run, then run it 
from a cronjob and put the output somewhere where it can be scraped (e.g. 
node_exporter textfile collector).  This is a good idea anyway for 
expensive metrics, as it avoids DoS problems if multiple clients are 
scraping the same exporter.

I can't really answer your other questions about staleness markers.  My 
understanding is that staleness markers are not exposed to users 
<https://www.robustperception.io/staleness-and-promql> (even though 
internally they're a special kind of NaN); so if you query a timeseries 
which is stale, I would expect that vector result would not include that 
timeseries - it would be just as if the timeseries did not exist at that 
point in time.  In other words, I'd expect that count(foo) would give the 
number of timeseries for metric "foo" which are not stale.  But that's just 
my expectation; you should test it if it matters to you.  It's completely 
different from the question you originally raised about stopping and 
restarting prometheus.

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