[rrd-developers] rrd file access code

Daniel.Pocock at barclayscapital.com Daniel.Pocock at barclayscapital.com
Mon Oct 13 18:07:08 CEST 2008

> what you might want to keep in mind is that I intend to 
> create a new platform independent file format. This will also 
> have an impact on this ... so if you are looking closely at 
> all this code, the fileformat work might be integrated ...
> what I have done so fahr is documented on 
> http://oss.oetiker.ch/rrdtool-trac/wiki/PortableRrdFormat

Ok, I will look over that.

What I have already implemented is my own open(), read(), write() and
close() functions for a striped file.  I would like rrdtool to call my
functions instead of the C library functions.  These functions do not
actually care too much about the format of the data within the stripes
(old format or new format RRD), the bigger issue for me is how to

Currently, I'm just replacing all the C library calls with some function
pointers in rrd_file_t.  The function pointers get initialised when the
file is opened.  This means that several back-ends could be in use

To maximise the benefit of the striping algorithm, there is some
additional code (which I'm yet to complete) which ensures that a newly
created RRD will have it's first CDPs stored at the same offset within
the RRD as the other stripes.  I'll try to generalise this concept to
work within your new framework.  Do you see any problem with bumping the
offset of a new RRD file in this way?

The algorithm is aimed at products like Ganglia, where all the RRDs are
the same size and updated at the same time.



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