[rrd-users] 5 minute data -- RRD

Simon Hobson linux at thehobsons.co.uk
Fri Jul 11 08:47:38 CEST 2008

James Wade wrote:

>I am using Hobbit and the RRD database for
>monitoring. If I'm collecting 5 minute data, when does the
>database begin rolling up the data (averaging it).
>Does it keep a months worth of 5 minute data
>and then does a daily average after a month?
>Is there a process that compacts the database?
>Just wondering how the process works.

First off, try Alex's excellent tutorials at 

But more specifically, each time you do an update, the program checks 
to see if any time boundaries have been passed. Eg, if you updated 
every minute for an rrd that has a 5 minute step size, then 4 time it 
will just accumulate the data, the fifth time (ie when you pass a 5 
minute boundary) it will process that step.

The consolidations are handled in a similar manner, so a 2 hour 
consolidation would be processed each time an update occurs that 
crosses a 2 hour sample period, and so on.

There is no database compaction, the rrd database is unique as far as 
I know in having a fixed size that is set when it is created. Each 
stored data set is held in a number of preconfigured storage bins - 
the bins having been allocated at the time the rrd file was created. 
Each set is treated as a circular buffer (hence the "round robin" in 
the name), so data is never moved, just the pointer to where the 
beginning/end is located gets altered along with the contents of that 

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