[rrd-developers] interleaving RRD files, RRDfs perhaps?

[Daniel.Pocock at barclayscapital.com]

> I think this leads to the rrd as a dbms discussion we touched 
> a few days ago on the list. This would open up up many 
> possibilities but also have to potential of makeing things a 
> lot more complex. In my eyes it is primarily a matter of 
> finding a really clever design for something like this.
>

It would be nice if rrdtool had some special way of interpreting the
filenames and mapping them to some kind of heirarchical dbms structure.
Then the application wouldn't need to know anything about what was going
on under the hood.

E.g. when the user does `rrdcreate /hostA/eth0_in.rrd ...', rrdtool
would:

- find a real file on disk containing DSes of the same format (same
step, same xff, etc), or create such a file with a predefined number of
empty DSes if it doesn't already exist

- make a record in some database associating /hostA/eth0_in with the
real filename and the internally assigned DS index

- subsequent calls to rrdupdate on /hostA/eth0_in.rrd would be mapped,
behind the scenes, to the real DS

Maybe the filenames could be given a URL-style prefix to indicate that
they are virtual?  E.g. rrd:/hostA/eth0_in.rrd

If they are just multiple DSes in a normal RRD file, there is a problem
of how to ensure they are all updated simultaneously.  However, if this
was an enhanced file format, then the DSes could have independent update
times - even if they were not always updated together, or even if they
are being updated by separate rrdupdate processes called from shell
scripts, the OS level write cache would still have a good chance of
doing it's job.

Regards,

Daniel
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