[collectd] network plugin questions

Florian Forster octo at verplant.org
Sun Apr 20 10:52:40 CEST 2008

Hi Oleg,

On Fri, Apr 18, 2008 at 07:17:51PM +0400, Oleg King wrote:
> 1. What is cache that controlled by CacheFlush setting?
> OK, plugin caches time values and flushes time values, but what for
> it needs/uses theese values?

for loop detection, mostly. So if you have two instances, and both are
set to `forward', you will not end up with an endless loop. Also, the
`Forward' option makes use of this cache.

In general, you shouldn't need to worry about that setting. The default
of 30 minutes should be okay for pretty much everybody ;)

> 2. If I reboot server with RRD database, all information from clients
> will be lost until server will not up again. May be, it will be
> useful to implement 3rd, TCP type of connection with acknowledges of
> data reception and caching unsent info on clients side until server
> will be able to receive info again?

I've been thinking about some sort of redundancy protocol, so that
several servers can work together and replace one another. I haven't
actually coded anything in that direction yet, though. If you're
interested in implementing anything, we should definitely talk about our
ideas ;)

> 3. As I understand, clients sends information with time of event, but
> this is clients time of event. So we need to syncronise time on all
> servers to get right slices of database info?

Why? If the load at time 8am was `100', why write that value as if it
appeared at 2pm, just because it took us a while to process the value?
Anyway, synchronizing the time of your servers is always a good idea, so
that logfiles and administrative emails end up with a right time in

> In one of my projects I calculate timediff between client and server
> and use this timediff to make all times syncronised. Will it be useful
> in collectd?

Ugh, time difference calculations are tricky. Very tricky, even. I'd
just install NTPd everywhere and be good..

> I will try to implement theese features anyway, because I need it, but
> may be I wrong somewhere?

Well, I use the time of the system collecting the data on purpose and
currently I don't see the point why this should be a bad thing. I see,
however, *a lot* of problems if you use the time of the system writing
the values to disk, because various levels of caching may be between
collection and storage of the values..

Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
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