[rrd-users] changing step time?

[Simon Hobson]

Gregory Guthrie wrote:

>1) What is the actual meaning of "step" - specifically what happens 
>if values are fed in more often?
>      The documentation says that if updates are less frequent, they 
>are interpolated (up to heartbeat), but I didn't see this converse 
>case.

Step is the size of each bin in the database - ie the length of each 
time slot for which it can store data. Anything you feed it more 
often that the step time is accumulated until the period is complete 
and then it's all used to work out the single value stored for that 
bin.

Eg, if you feed in values of 0,0,5,0,0 which all fit within one step 
time, then the min, max, and average are all 1.

Alex has some excellent tutorials at 
http://www.vandenbogaerdt.nl/rrdtool/ - they explain a lot.

>2) Can I change step after the database is created?
>   - I setup one value for daily step size, but now want to do 
>twice-daily updates.
>   - Can I change step size, and just start inserting updates more often?

Don't think so. I think you have to dump the data then do one of two things :
1) create a new database and feed the old data in
2) edit the data and re-import it

>3) If I were to re-create the database, is there any (easy) way to 
>preserve the data already collected?
>
>4) If I have a few known initial values, can I insert them into a 
>live rrd database using the rrdedit tool?
>    I tried to do this using rrdtool, but got this error:
>       illegal attempt to update using time 1262354400 when last 
>update time is 1270818003 (minimum one second step)

You cannot go backwards in time. So to put historical data in, you 
must doing before putting current data in. So create a new database, 
craft some insert statements to enter the historical values, and then 
start inserting new data.

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Simon Hobson

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