How to keep track of number of Active users in Graphite

Question

I need to keep track of the number of Active user on my web site at any point of time . For this i am incrementing a key named "users.loggedin" every time a user log-in and decrements it, every time a user signs out.

I am sending my metrics to Graphite via StatD. But based on what i have read "Increment" gives the changes per time interval thus I could see the changes in the Graphite Dashboard, but it shows zero again after some time.

Answer 1

Configure Graphite for StatsD

Did you configure Graphite for usage with StatsD? You must specify in Graphite configuration how you expect it to handle the data you are sending from StatsD. This is important because Graphite could be averaging your counts instead of summing them.

If sending sparse or "bursty" data

Confirm that your xFilesFactor is low enough that aggregation produces non null values even with a high rate of nulls. For example, 100 requests in the first 10 seconds, and none for the remaining 50 seconds in a minute would cause a storage of 100, null, null, null, null, null which would be summed up to null when the data ages if the XFilesFactor is higher than 1/6. Using the statsd recommended graphite configuration handles this, but it is good to know about... as this can give the appearance of lost data.

Saving schema or aggregation changes

If you changed the graphite schema or aggregation settings after any metrics were stored (in whisper = graphite's storage) you'll need to either delete the .wsp files for the metric (graphite will recreate them) or run whisper-resize.py.

Validating settings

You can verify the settings against some whisper data by running whisper-info.py on a .wsp file. Find the .wsp file for one of your metrics in /graphite/storage/whisper/ Run: whisper-info.py my_metric_data.wsp. whisper-info.py output should tell you more about how the storage settings are working.

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After you've confirmed that your data is accurate, then I'd move on to creating the graph you want in the UI:

You might need to use the hitcount() function for this.

This post covers what you are after pretty well (even if you aren't using StatsD).