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[mikelehen <question205258@xxxxxxxxxxxxxxxxxxxxx>]

Question #205258 on Graphite changed:
https://answers.launchpad.net/graphite/+question/205258

Description changed to:
The docs (http://graphite.readthedocs.org/en/latest/whisper.html
#archives-retention-and-precision) say:

To support accurate aggregation from higher to lower resolution
archives, the number of points in a longer retention archive must be
divisible by its next lower retention archive. For example, an archive
with 1 data points every 60 seconds and retention of 120 points (2 hours
worth of data) can have a lower-resolution archive following it with a
resolution of 1 data point every 300 seconds for 1200 points, while the
same resolution but for only 1000 points would be invalid since 1000 is
not evenly divisible by 120.

So this is saying "1m:2h,5m:6000m" is valid, but "1m:2h,5m:5000m" is not
valid?  I haven't dug into how whisper aggregation works, but this
surprises me.  It doesn't seem like the number of data points should
matter at all, but rather the resolution of the archives is what seems
important to me.  That is, since 5 minutes is a multiple of 1 minute,
whisper should be able to take 5 data points from the first archive and
turn it into a single data point in the second archive, without loss of
precision.  Why does the total number of data points matter?

Questions:
1. Are the docs wrong or am I missing something?
2. If "1m:2h,5m:5000m" is invalid, why doesn't carbon complain if I use it?  Is this a bug? (carbon-cache starts successfully and I don't see any errors in console.log)

Suggestion: It sure would be handy to have some example retentions
policies to choose from.  I feel like this is probably an important /
hard-to-change setting, but I don't have a good intuition about what a
good policy might look like.

Thanks!
-Michael

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