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From Larry <larryr...@gmail.com>
Subject Re: Understanding CouchDB stats
Date Thu, 22 Oct 2009 22:08:02 GMT
Great, Thanks!

On Thu, Oct 22, 2009 at 2:46 PM, Paul Davis <paul.joseph.davis@gmail.com>wrote:

> >   1. What exactly is 'current' & 'count'. What are each of them recording
> >   and why is 'count' less than 'current' in my system (seems counter
> intuitive
> >   to me).
>
> Current is a sum of the values recorded. For things like HTTP
> requests, this is the total number of requsts.
>
> Count is the number of updates for this metric in the given time span.
>
> Stats works with two parts, a collector and an aggregator. The
> collector part receives messages from through out CouchDB and holds
> that data in a table. Once a second the aggregator will sweep through
> the collector and update its stats.
>
> So, if you had 20K requests between to aggregator sweeps, Current
> would be incremented by 20K and Count is incremented by 1.
>
> >   2. Can the 'mean' here be interpreted as average reads per second?
>
> For requests, the mean is roughly the requests per second. Its not as
> theoretically correct as something like RRDtool because we don't
> interpolate, we just average the reads we take roughly once a second.
>
> >   3. Is there any indication of exactly where within the 5 minute
> interval
> >   we are?
> >
>
> No, but the current implementation (committed after 0.10.x was
> branched) does not reset statistic aggregators as the old code did.
> The new method is the more standard "these stats reflect all values
> seen in the last 5 minutes" regardless of when you query it.
>
> > Another metric that I'm having trouble with is the 'request_time'.
> Querying
> > it returns data similar to:
>
> [snip]
>
> >   1. Again, same question about exactly what the 'count' and 'current'
> >   values mean for this metric.
>
> Oh weird. So, Count has the same meaning as before, but here Current
> is the length of the last recorded request. The weirdness comes from
> the fact that this is averaging a set of distinct points, where as
> things like requests are averaging the relative change so current
> makes a bit more sense there.
>
> >   2. Does the 'mean' represent the average time for a request in CouchDB
> in
> >   seconds?
>
> milliseconds.
>
> HTH,
> Paul Davis
>

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