[rrd-developers] Add `FETCH' command to rrdcached

[Florian Forster]

Hi Tobi,

On Mon, Apr 06, 2009 at 05:11:25PM +0200, Tobias Oetiker wrote:
> I would want to schedule this for 1.5 though and not rush it into 1.4

I'd prefer to see this in 1.4, since I hope that the possibility to
create graphs without physical access to the RRD files will be welcome
by many. The changes to ‘rrd_daemon.c’ and ‘rrd_client.[ch]’ are not
exactly nice, but simple, so the number of new bugs in that code is
hopefully low.

I have to admit I wasn't away that version 1.4 was due soon. Is there
information available regarding the release plans?

> a) looking at the patch I see that the flushing operation is
>    included in rrd_graph (this is not new).

It is? I can't find it:
-- 8< --
 octo at leeloo:~/rrdtool-trunk.git $ git branch | fgrep '*'
 * ff/rrdc_fetch
 octo at leeloo:~/rrdtool-trunk.git $ grep -i flush src/rrd_graph.c || echo "No match"
 No match
-- >8 --

Anyways, the changes made to ‘rrd_{fetch,graph}.c’ were meant for
discussion only, and I think we've reached the consensus that including
a daemon address on a per-file level is preferable to the existing code.

>    - when called with normal filenames, the code would acct
>      accoring to the environment variable settings or the --daemon
>      setting.
> 
>    - alternatively rrd_graph (rrd_fetch) should support a extended
>      filename syntax: port at server/rrd_path (I am not using :port
>      since : is already a separator in the rrd_graph syntax

I propose a slightly different approach:

 - ‘rrdtool fetch’ behaves as implemented in my third patch, i. e. if a
   daemon address is known, it will send a ‘FETCH’ command instead of a
   ‘FLUSH’ command.
  
 - The ‘DEF:’ syntax is extended to recognize the ‘address’ (or ‘daddr’
   for “daemon address”) and ‘port’ (or ‘dport’) options, for example:

     DEF:foobar=/path/to/file:AVERAGE:address=my.server.tld:port=12345

   I think this is less magicy than adding special syntax to the
   filename and therefore easier to comprehend. Also, this keeps magic
   out of `rrd_fetch' and keeps the distinction clear and easy:

    * ‘rrd_fetch’ and ‘rrd_fetch_r’ are for local file access.
    * ‘rrdc_fetch’ is for remote file access.

> finally, I am planning to add shared secret based authentication to
> 1.5 so that one can use the cached over the network even when the
> network is not inside a firewalled cluser.

Sounds good :)

Regards,
-octo
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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