rrdtool - Playing with rrdtool counter resets

http://zewaren.net/site/node/141 

Playing with rrdtool counter resets

Fri, 2014-12-05 09:10 — ZeWaren

Not so frequently asked questions and stuff: 

Programming

Creating and plotting some data normally

Let's create a standard rdd file, with a counter:

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1	rrdtool create test.rrd --start $start --step 60 DS:something:COUNTER:600:0:U RRA:AVERAGE:0.5:1:1440

Now let's update it with some values.

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#!/usr/bin/env perl -w   use strict; use warnings;   my $start = 1417392000; my $counter = 0;   for my $x (1..60*24) {     my $time = $start + 60*$x;     $counter += 1000+ int(250*sin(1/(48)*$x));     my $command = "rrdtool update test.rrd $time:$counter";     system($command); }

Let's graph!

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rrdtool graph test.png -a PNG --start 1417392000 --end 1417478400 -t "Sure looks like a sine" -v "avg potato per second" \     DEF:something=test.rrd:something:AVERAGE \     LINE1:something#111111:"My superb value"

So far, so good.

Having a counter reset

Now, let's recreate the same data, but with a counter reset in the middle.

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if ($x == 1000) {     $counter = 0; }

The dreaded spike appears!

Folder http://oss.oetiker.ch/rrdtool/pub/contrib/ contains many tools to remove spikes from rrd data files. My favorite one is spikekill (spikekill-1.1-1.tar.gz).

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1	php removespikes.php -d -A=avg -M=variance -P=5000 -R=test.rrd

The spike is then replaced by a small innocent glitch.

To prevent counter reset spikes, you should use DERIVE instead of COUNTER. Tuning the rrd file solves the problem.

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1	rrdtool tune test.rrd --data-source-type something:DERIVE