SOFTWARE ENGINEERING blog & .lessons_learned
manuel aldana
Manuel Aldana

July 3rd, 2011 · No Comments

Accessing rrdtool-files Data with Java / Scala

Though rrdtool is widely used especially for monitoring, it took me a while to find a simple and compatible bridge for reading data of rrd-files with Java. Following hopefully helps others to save some time and to workaround some pitfalls.

My requirement was:

  • Monitoring website showing trends of metrics, i.e. compare current with past values, both absolute and relative (hour over hour, day over day, etc.).
  • Data backed is round-robin-database. The rrd-files are generated by munin (with under the hood rrdtool). Data should be accessed read-only.
  • Website’s technology stack is Java based (Play! framework with Scala integration).

Because I use Play! framework I needed a way to access rrd-files with Java-Technology. My first look at rrd4j looked promising but failed, because rrd4j is a port and cannot read rrd-files created by original rrdtool. After some time-consuming research and Google-digging I finally stepped over java-rrd.

Installation Steps java-rrd

I couldn’t find the library built and distributed in any Maven-repository, so you have to download + build yourself:

# download + unpack
tar xfz <downloaded-tarball.tar.gz>
# build .jar library with Maven
cd <untarred-directory>
mvn package
cp target/*.jar <your-target-lib-folder>

Instead of dump-copying and to be more clean with your build-system you might want to deploy the .jar file to a repository like Nexus.

Read-Access Usage java-rrd

As I use Play! framework with Scala integration, Scala was the integration way:

import net.stamfest.rrd._
val rrd = new RRDp(“/tmp”, “55555″)
val command = Array(“fetch”, “your-rrd-file.rrd”, “MAX”, “-r”, “1800″, “-s”, “-1d”)
val result = rrd.command(command)

if (!result.ok)

For completeness another snippet in Java source language:

import net.stamfest.rrd.CommandResult;
import net.stamfest.rrd.RRDp;
RRDp rrd = new RRDp(“/tmp”, “55555″);
String[] command = {“fetch”, “your-rrd-file.rrd”, “MAX”, “-r”, “1800″, “-s”, “-1d”};
CommandResult result = rrd.command(command);

if (!result.ok)

With java-rrd you can also access rrdtool over sockets/network.

Parsing rrdtool output

rrdtool output after fetch is plain text, something like:


920804700: nan
920805000: 4.0000000000e+02
920805300: 2.0000000000e+03
920805600: 0.0000000000e+00
920806800: 3.3333333333e+01

Above needs to be processed further to be “structured enough” for your code. For example do following (I only show Scala, I skipped Java iterating syntax hell…, did I mention that I love passing functions ;):

def outputToNumberPairs(rrdFetchOutput: String) = {
    // filtering unneeded + empty lines
    val list = rrdFetchOutput.trim().split(\n).filter((n) => n.contains(“:”) && !n.contains(“nan”))
    // parsing strings to numeric values and combine to pair
    for (i <- list) yield i.split(“:”)(0).trim().toLong -> i.split(“:”)(1).trim().toFloat.round
res34: Array[(Long, Int)] = Array((920805000,400), (920805300,2000), (920805600,0), (920806800,33))

Tags: Technologies/Tools

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