[rrd-developers] Re: rrd format change ?

[Alex van den Bogaerdt]

Jake Brutlag wrote:
> 
> Tobi wrote:
> > so if we can find a format for rrd which is better to accomodate
> > future changes, I think it would be  worth while doing the changes
> > now, and find a way to keep on reading old rrd files instead of
> > adding more hacks and going to a better ormat later having evben
> > more difficulty supporting old stuff ?
> 
> Okay, so if we are going do this, I think the first step is to abstract
> the RRD header from the rest of code. The core files, such as
> rrd_update, rrd_create, etc make extensive use of the internal structure
> of the header. If the header was encapsulated and only accessed by a set
> of accessor functions (obviously I'm thinking in C++, but this is doable
> in C), the the other files need not be aware of the format on disk of
> the header. The header format can change and the other files (update,
> create, dump, restore, info, etc) remain unchanged. This encapsulation
> would also confine changes to support different file versions to the
> code for processing the header (well, as long as the only the header
> changed for different versions).

Maybe I don't get it but why change the header at all.  If there
is nothing changed in what the header describes, an older version
of RRDtool is capable of reading all of the data in the RRD. Any
new stuff can be in either a separate file, or appended to the RRD
and this is not processed by that version.  The data that it can
find, it can process.

A newer version of RRD can easely extend an already existing RRD and
can do so without needing to modify the header. Just add a new header
describing the new stuff at the start of the new part.

Maybe do something similar as the GIF format has, introduce a type
and lenght field in the header, so that parts can easely be added?

cheers,
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