[rrd-developers] [rrd] Re: exporting cf_conv

[Tobias Oetiker]

Hi Bernhard,

Today Bernhard Reutner-Fischer wrote:

> On Wed, May 27, 2009 at 08:25:32PM +0200, Bernhard Reutner-Fischer wrote:
> >On Tue, May 26, 2009 at 01:42:57PM +0200, Tobias Oetiker wrote:
> >>Hi Bernhard,
> >>
> >>Today Bernhard Reutner-Fischer wrote:
> >>
> >>> On Tue, May 26, 2009 at 09:17:59AM +0200, Tobias Oetiker wrote:
> >>>
> >>> >finally getting ready to publish 1.4rc I have resolved the
> >>>
> >>> btw.. Can we please have cf_conv exported since otherwise
> >>> it is not really possible to do anything useful with the
> >>> library.
> >>
> >>:-) interesting notion ... you mean all uses of the library up to
> >>now have not been useful ?
> >
> >I don't know, but my usecase needs it exported from the beginning.
> >I admit that i have _no_ idea how other users of the library
> >look like, but i wouldn't be surprised if they were just using
> >some high-level view without having to worry about performance :)
> >>
> >>please elaborate.
> >
> >Suppose i want to get some values out of an rrd (like i mentioned before
> >in the sample-code here ¹) in the _fastest_ possible way and you have an
> > rrd with say X ds and Y cf and only want to get ds_something with cf
> >LAST, then you somehow need to get at the appropriate data.
> >
> >Note, that i cannot afford to waste any unwarranted cycles to get at that
> >data, so high-level scripting languages and stuff like that are a nono,
> >I have to rrd_open() the file, get at the data and interpret the values
> >often, very often and as fast as possible. Since i need only current
> >data in 99.9% of the accesses (and no older data), it of course helped
> >to also keep the "hot" regions in memory as much as possible. But anyway.
> >
> >I would be more than happy to be able to reuse more of the existing
> >code of librrd as you can see about all except the setup and reporting
> >in the sample application is just taken 1:1 from rrd_fetch() (IIRC).
> >
> >See?
> >
> >¹)
> > http://www.google.at/search?hl=en&num=50&q=rrd_reader&btnG=Search
>
> I've put my current incarnation here, fyi:
> wget -cN http://busybox.net/~aldot/rrdtool/rrd_reader.{c,h} && \
> gcc -O2 $CFLAGS -o rrd_reader rrd_reader.c -I/opt/rrdtool/include
>
> rrdtool-1.4, user-friendly C API, platform independent format sound
> somehow familiar :)
> If you're thinking about doing an 1.4-rc, then i encourage you to
> look at the sample user above. Ideally, such a thing would just
> consist of (quote from ¹ above):
> ---8<---
> You can see how i had to:
> a) duplicate basically all of rrd_format.h
> b) had to duplicate those parts of fetching values that deal with the
> calculation of the locus of the data we need.
>
>
> The applet should basically do this instead:
> 0) [APP] option handling
> 1) call rrd_open()
> 2) [APP] eventually inspect the header.
> 3) [APP] setup desired start, end, step.
> 4) call rrd_find_rra() or rrd_find_best_rra() /* or however it would be
>    called */
> 5) [APP] adjust start, end, step to legit values.
> 6) call rrd_fetch_fn()
> 7) [APP] rrd_close(); rrd_free()
> 8) [APP] do something with the results and exit.
>
> Where stuff marked with [APP] is ok to be done by the application, but
> the rest (points 1, 4, 6) should be just simple calls into librrd.
> ---8<---
> http://www.nabble.com/-PATCH-%2B-RFC--Cleanup-the-symbols-exported-by-librrd.-tt17719839.html#a17732207

ah, now I remember ... well I'm afraid this is not a level of rrd
introspection I want to support with the current rrd format, since
the more api code I expose for these kind of operations, the more I
will have to support which I don't want todo with the present api
...

I'm afraid for now you will have to duplicate code ... or link
staticaly.

this will get better with the portable rrd format as I plan to
create a set of accessor functions for it which will also be
exposable ...

hope this helps ...

1.4 is mainly about rrdcached ...

cheers
tobi

>
> cheers,
> Bernhard
>
>

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900