[rrd-users] Re: Adding DS's - without import/export?

[Alex van den Bogaerdt]

Jason Fesler wrote:

> I'm stumbling my way into actually adding a "addds" command into rrdtool.
> It is really fun walking into someone else's code and trying to peice
> things together (grin).  I may need to poke you if I get stumped (I got
> sidetracked today).  I *hope* to have something that looks like it works
> for me, in which case I'd love for you to code review it and possibly put
> it into rrdtool.  I'm picking apart parts of rrd_dump.c and rrd_restore.c
> to try and figure out what I need to do.
> 
> As I understand, rrd_restore actually builds from XML, a complete rrd
> "image" in memory.  My current goal is to read an existing rrd file, add
> in the extra ds entry, fill in the appropriate fields, and actually
> populate the data, then use rrd_write from rrd_restore.c to write a new
> file to disk.

I think you should probably do this differently.  Basically the RRD
file format is a number of RRAs, each RRA being built from a number
of rows, each row being built from a number of CDPs.  What you need
to do is:

   read the original header
   change number of DSes
   write it to another file
   for each RRA {
      for each row {
         for each original ds {
            read value from original file
            write value into new file
         }
         write new ds value(s) into new file
      }
   }
   rename file over original file

Let the OS handle efficiency, it should read and write blocks anyway.
I think this approach is more easy and thus less prone to errors.

> wish me luck..

Good luck!

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