[rrd-users] scaling rrd - file format question

Ryan Kubica kubicaryan at yahoo.com
Fri Oct 22 21:00:15 CEST 2010

RRD Developers,

I have the need to pre-create rrd datapoints before they are used; such that 
there are already existing datafiles on the filesystem which are in a free pool 
and used when required.

The problem is that without a free pool the system is creating the datapoints on 
demand when newly monitored data is being inserted.  That for the most part is 
okay if the new datapoint count is low thousands.  However the issue arises when 
>50 thousand datapoints are required quickly.   Creating them causes noticable 
latency in storing all new datapoint data.

So the answer seems to be pre-create.
The concern I have is in the past (5 years ago) I tested creating rrd data files 
with an RRA of 1 year of data and the create time set to unix epoch.  When doing 
an update to that file it seemed like the entire rrd was rewritten since none of 
it's 'intervals' were valid for the update time of 'now'.

Does the latest 1.4 version do the same thing?

Or is it essentially a no-cost-difference in IO to update an rrd with a start 
time (and thus round-robin end time) with a time interval in the future of it?

I don't want this feature to have a negative impact on IO in nearly the same 
manner as creating them would be.

I could try and test it, but RRD developers will know for certain what the total 
cost is, which is what I'm most interested in.



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