[rrd-developers] Re: rrd format change ?

[Alex van den Bogaerdt]

Tobias Oetiker wrote:

>  | 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.
> 
> my intention when designing the rrdtool format was to have a header
> at the beginning of the file which describes the whole file
> structure, and thus saves us from having to seek through the whole
> file hunting down extension headers ...

OK, clear.

> the intention behind changeing the header format is to make it even
> more flexible by allowing configurability of the data sections of
> DS and RRA header areas ...

>  | 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?

So:
<total length> [ <code><length><part-of-header> ... ] <end tag> <data>

File format will change, one time.  After this, you have defined
(for instance) 2^32 different element types in advance and only
need to define which element is which (for instance in rrd_header.h).

cheers,
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