Re: Using functions in the graphite web-api of pmwebd

Hi Frits,

----- Original Message -----
> Hi everybody,
> 
> I tried using grafana (both the version that comes with the pcp rpm’s and the
> latest version) to create some dashboards of PCP archives. When doing this,
> you quite quickly run into the need to do conversions (huge pages are
> calculated in pages, whilst other memory components are calculated in Kb,
> which is how /proc/meminfo externalises this information, as an example).
> 

FWIW, that's a bug - hugepages stats not being available in correct units -
I'll fix that up (we'll need to add some new metrics with appropriate units
alongside the existing ones I guess).

> However, whenever doing so, grafana indicates there is no data to display.
> Upon investigating further, it turns out this is because grafana uses the
> graphite web-api, which, when for example a simple ‘alias()’ function is
> added to the request, simply does not return anything. To make sure it’s not
> grafana, but really the graphite interface, I used the graphite interface
> and did the same (added the alias() function), which gives exactly the
> result: no data/response.
> 
> Is this intended behaviour? Indeed

There seems to be alot of cases of missing/sub-optimal error handling in the
web API(s) unfortunately.  You might find something was logged in pmwed.log,
which usually resides in /var/log/pcp/pmwebd/ (depending on platform).

> http://pcp.io/man/man3/pmwebapi.3.html#lbAN
> <http://pcp.io/man/man3/pmwebapi.3.html#lbAN> clearly says ‘emulate a subset
> of the graphite web-api’, however it costed me quite some time to get to the
> bottom of this, mainly because of the absence of an error; a response
> telling it is not supported would be much more clear.

+1

From a quick browse of the code, there seems to be no code to support "alias"
in pmwebd.

> If that is intended behaviour, it would mean doing even simple investigations
> is severely constrained. What would be the other options of simple
> (historical) investigations of pcp archives? Currently it seems I first need
> to import them in any of the database backends that grafana supports?

If non-web interfaces are an option for you, pmchart and the console tools like
pmlogsummary, pmdiff, etc are good options.

cheers.

--
Nathan

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