A very simple script to merge multiple RRD files, since none of those available seem to work.

simple-rrd-merge.py

#!/usr/bin/env python

"""Simple script to merge multiple RRD files together.

Accepts any number of RRD file names as arguments.  Produces an "rrdtool dump"
style file on stdout.  The last RRD file should have a slot for every possible
record in the resulting merged RRD.

Run something like:
$ python simple-merge-rrd.py filea.rrd fileb.rrd filec.rrd | \
    rrdtool restore /dev/stdin merged.rrd
"""

import re
import subprocess
import sys


def main():
  rrd_data = {}
  rrds = sys.argv[1:]
  last_rrd = len(rrds) - 1

  for i, rrdname in enumerate(rrds):
    p = subprocess.Popen(
          ('rrdtool', 'dump', rrdname), stdout=subprocess.PIPE)
    for j, line in enumerate(p.stdout):
      m = re.search(r'<cf>(.*)</cf>', line)
      if m:
        cf = m.group(1)
      m = re.search(r'<pdp_per_row>(.*)</pdp_per_row>', line)
      if m:
        pdp = m.group(1)
      
      m = re.search(r' / (\d+) --> (.*)', line)
      if m:
        k = cf + pdp
        rrd_data.setdefault(k, {})
        if ('NaN' not in m.group(2)) or (
            m.group(1) not in rrd_data[k]):
          rrd_data[k][m.group(1)] = line
        line = rrd_data[k][m.group(1)]

      if i == last_rrd:
        print line.rstrip()


if __name__ == '__main__':
  main()

This tool does not properly work with RRDs generated by smokeping.
The reason is apparently that smokeping RRD's have "uptime" record that is NaN all the time.
to merge smokeping RRDs, we need to check if all columns are "NaN", not only one (since that test will always be true).

Thx for the script :)
Used it to merge munin history (not beautiful at all): https://gist.github.com/TuningYourCode/d1edb8b525bcc46dcafe308c030f742a

Worked great for combining nagiosgraph!

simple-rrd-merge.py PING*pl.rrd | rrdtool restore /dev/stdin pl.rrd

Thank you for this @arantius, worked perfectly.

thank you , it is working properly

hi . i use this command as below
python simple-rrd-merge.py old/pop_site_tavanir04_traffic_in_28871.rrd new/pop_site_tavanir04_traffic_in_28871.rrd | rrdtool restore /dev/stdin merged.rrd
but i got this error:
ERROR: mmaping file 'old/pop_site_tavanir04_traffic_in_28871.rrd': Invalid argument

i want to merge rrd file because i have gap between out graph

Hi! Using the tool as below:

./rrd_merge.py var/pnp4nagios/perfdata/host1/CPU_load_load1.rrd CPU_load_load1.rrd | rrdtool restore /dev/stdin merged.rrd

I got this error:

 File "rrd_merge.py", line 45
    print line.rstrip()
          ^
SyntaxError: invalid syntax
/dev/stdin:1: parser error : Extra content at the end of the document

^
ERROR: error reading/parsing XML: Extra content at the end of the document

In my case the problem was python3
As I haven't the permission to do a "PR" I forked this git.
The changes are available here:
https://gist.github.com/m3rlinux/e0ebe1fba39789f27209577cf4a08685

Indeed, this script is over 10 years old and was written for Python 2.

Yes! But it works like a charm with little changes ;)

It works perfect! Thank you!