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

[Holger Jahn]

Fabien,

In exactly this very minute I have been about to write to the list
regarding the same matter.

We are using RRD files which are 1.8GB each (800 RRAs per file with 5
mins resolution for one year), and when I generate a graph out of the
RRAs it works file with time periods "Now => 2 Weeks back". Every
attempt to generate graphs that span a larger time period, such as half
a year, ends up pushing our server into memory swapping.

Related info I have found so far is only this posting here:
http://www.linuxarkivet.se/mlists/rrd-users/0109/msg00065.html

"rrdtool loads ALL the data it uses to build the graph into memory
... and because processes can not give back any memory they can not
shrink ..."

and 

"If you are using wide rrds (many DS) memory consumption will also
be higher because rrdtool graph keeps data for all DS in memory not
only for the one you selected ... this could be improved by
modifying rrdtool graph and potentially rrdtool fetch"

I wonder whether it would be possible to circumvent this behaviour,
either by dumping the RRAs that are about to be graphed into a temporary
RRD file, or by only processing RRAs which are relevant to the
particular graph.

Hope someone with a more in-depth understanding of how RRD:graph works
can shed some light on this.

Many thanks,

Holger

-----Original Message-----
From: rrd-users-bounce at list.ee.ethz.ch
[mailto:rrd-users-bounce at list.ee.ethz.ch] On Behalf Of Fabien Wernli
Sent: Monday, 5 December 2005 9:14 a.m.
To: RRDTool List
Subject: [rrd-users] Memory usage on large RRAs

Hi,

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.

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