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I have been doing a lot of work lately with creating new data points to monitor with cacti and when trouble shooting why a new data point is not working I have been running into a bit of an issue.  I can see what my script is handing to the cacti poller, I can see what cacti is putting in the RRD file (with increased logging), but I can’t easily see what RRD has done with that data before handing off to cacti.  By default RRD store’s the time stamps in Epoch Time (seconds since midnight on Jan 1st, 1970) and data in scientific notation. Now, I don’t know about you, but I can’t read either of those without some help so here is my little Ruby script helper

#!/usr/bin/env ruby
# Author: W. David Nash III
# Version 0.1
# August 3, 2009

count = 0
STDIN.each do|l|

        count += 1

        printf("%-3i | ",count)

        if !l.match(/^\d+/)
                header = l.to_s.split
        else

                (td, data) = l.split(/:/).map
                time = Time.at(td.to_i)
                printf("%s:", time.strftime("%Y-%m-%d %H:%M:%S"))

                data.to_s.split.map do |d|
                        if (d.eql? "nan") then d = "0.00" end
                        printf(" | %20.2f", d.chomp)
                end
        end

        if(count == 1)
                printf("%20s", "Time")
                header.each do |h|
                        printf(" | %20s",h)
                end
        end
        puts "\n"
end

and you use it like so

rrdtool fetch rra/.rrd AVERAGE -s -1h -r 60  | ./readRRD.rb

and here is some sample output

1   |                 Time |   Heap_Mem_Committed |         Heap_Mem_Max |        Heap_Mem_Used | Non_Heap_Mem_Commit |    Non_Heap_Mem_Init |     Non_Heap_Mem_Max |    Non_Heap_Mem_Used |             CPU_TIME |            User_Time |         Thread_Count |    Peak_Thread_Count |        Heap_Mem_Init
2   |
3   | 2009-08-03 13:18:00: |         213295104.00 |         532742144.00 |         130720632.67 |          36405248.00 |          12746752.00 |         100663296.00 |          36383328.00 |         623333333.33 |         531666666.67 |               111.33 |               184.00 |                 0.00
4   | 2009-08-03 13:19:00: |         213295104.00 |         532742144.00 |         132090801.60 |          36405248.00 |          12746752.00 |         100663296.00 |          36383328.00 |        1818000000.00 |        1704000000.00 |               111.80 |               184.00 |                 0.00
5   | 2009-08-03 13:20:00: |         213295104.00 |         532742144.00 |         122721880.67 |          36405248.00 |          12746752.00 |         100663296.00 |          36383328.00 |        2186666666.70 |        2057500000.00 |               112.92 |               184.00 |                 0.00