[rrd-developers] Re: rrd format change ?

Jake Brutlag jakeb at microsoft.com
Mon Mar 12 17:18:32 MET 2001

> How about having the rrd format changed so that at the beginging
> of the rrd we have some size specifiers which tell how large the
> data area of each DS definition is ... this would allow to create
> some sort of forward compatible system which can skip DS types it
> does not understand ...

Obviously there are some problems that changing the format could resolve,
but I didn't want to be the one to propose it. In a past life (okay, just 5
years ago), I was working in tech support for a small database company and
there I learned that backwards compatibility is high priority. In the
current design, RRDtool can support version 1 and version 2 RRD files
without effort. If the format was changed, the code would need to branch to
preserve backwards compatibility.

Another personal issue with backwards compatibility is Cricket code. For
some reason, there is code used in Cricket to read the binary header
sections of an RRD file. Now this is very poor design (for which I am not
responsible), but Cricket utilizes the fact that data sources (and
everything else in the RRD header) are of a predictable fixed size. Of
course, this code could be changed, and would have to be if the format of
the RRD header changed.

On the otherhand, both the aberrant behavior detection and the COMPUTE data
source implementation had to jump through some hoops to fit within the
current RRD header structure. If a new, more flexible format, was selected
some of the ugliness could be cleaned up.


Jake Brutlag (jakeb at corp.webtv.net)
Network Analyst
Microsoft WebTV 

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