[rrd-users] Re: Memory usage on large RRAs

[Holger Jahn]

What happens if resolution equals to 5 minutes, step equals to 1 day,
time period equals to a year, there are 800 DSes in the RRD file, and
one creates a graph with 1 DS out of the RRD database?

Will RRD read all PDPs (in 5 mins resolution) x 800 DSes for one year
out of the file, or will it skip the 287 5minute intervals between each
relevant PDP of each DS?

Cheers,

Holger

-----Original Message-----
From: rrd-users-bounce at list.ee.ethz.ch
[mailto:rrd-users-bounce at list.ee.ethz.ch] On Behalf Of Alex van den
Bogaerdt
Sent: Monday, 5 December 2005 11:16 a.m.
To: RRDTool List
Subject: [rrd-users] Re: Memory usage on large RRAs

On Sun, Dec 04, 2005 at 09:14:19PM +0100, Fabien Wernli wrote:

> I am monitoring ~700 nodes using rrdtool, each updating 7 databases on
a
> central server.
> 
> Does anybody have experience on writing DEFs and CDEFs to minimize
memory
> usage? At the time being I am unable to successfully plot a cumulative
graph
> of all nodes, as memory runs out.

Each DEF and CDEF will consume memory.  You can start by getting rid of
as much CDEFs as you can.  Simple example:
  Don't do:
    DEF:ds0_bytes=....
    CDEF:ds0_bits=ds0_bytes,8,*
    CDEF:ds0_unknowntozero=ds0_bits,UN,0,ds0_bits,IF

  Do:
    DEF:ds0_bytes=....
    CDEF:ds0_unknowntozero=ds0_bytes,UN,0,ds0_bytes,8,*,IF


Another important step: make sure to use the right RRA.  If you are
going to graph many days in a single graph, it makes no sense to use
the 5-minute data to do so.  Using "now" (implied or not) for start
and/or end is almost always guarantied to cause this problem.  Make
sure to set start and end to a whole multiple of step*steps, and
make sure the amount of pixels corresponds with the amount of data.


Do you save lots of correlated stuff in the database?  If you are only
using two out of ten DSes, RRDtool still fetches all ten DSes.  It may
make sense to, for instance, keep ethernet errors in a different file.

-- 
Alex van den Bogaerdt
http://www.vandenbogaerdt.nl/rrdtool/

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