Change Interval in Munin With Existing RRD Data

The default settings for Munin will result in RRD files containing 5 minute intervals of data, or 300 seconds as it is stored internally. It is possible to change this interval by changing /etc/cron.d/munin. It’s also necessary to change the update_rate in your Munin configuration, usually found in /etc/munin-node.conf. This value should match the resolution of the munin cron.

If you make this change before you start collecting data, great! If you do already have historical data that you want to keep, you need to convert the data to work with the new interval. The only documentation I was able to find on this matter on the Munin site was issue #1282 update_rate needs documentation, which in turn referenced http://www.elturista.net/2012/01/02/changing-step-time-of-a-rrd-file/ however this file is no longer available. I was able to locate it using the WayBack Machine, and in the interest of preservation I am reposting here with additional updates of my own.

rrdtool dump file.rrd > file.5.xml
./rrd_step_reduce.py file.5.xml 5 > file1.xml
rrdtool restore file1.xml file.rrd

#!/usr/bin;/python
# -*- coding: utf-8 -*-

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import sys
from copy import deepcopy
from StringIO import StringIO

try:
    from lxml import etree
except ImportError:
    try:
        import xml.etree.cElementTree as etree
    except ImportError:
        try:
            import xml.etree.ElementTree as etree
        except ImportError:
            try:
                import cElementTree as etree
            except ImportError:
                try:
                    import elementtree.ElementTree as etree
                except ImportError:
                    raise

def main(dumpfile, factor):
        
    xmldoc = etree.parse(dumpfile)
    root = xmldoc.getroot()
    
    # change step, reducing it by a factor of "factor"
    step = root.find("step")
    assert(step!=None)
    old_step = int(step.text)
    new_step = old_step/factor
    step.text = str(new_step) 
    
    database = root.findall("rra/database")
    for d in database:
        index = 0
        count = len(d)
        while count > 0:
            for i in range(0, factor-1):
                #d.insert(index+1, NaNdoc.getroot())
                d.insert(index+1, deepcopy(d[index]))
            index = index + factor
            count = count - 1
    
    print etree.tostring(root)

if __name__ == "__main__":
    # arguments
    if len(sys.argv) != 3:
        print "rrd_step_reduce.py rrddump.xml factor"
        sys.exit(-1)
    
    # call main
    main(sys.argv[1], int(sys.argv[2])))