[rrd-users] scaling rrd - file format question

Tobias Oetiker tobi at oetiker.ch
Fri Oct 22 23:29:25 CEST 2010

Hi Ryan,

Today Ryan Kubica wrote:

> 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.

there is no smartness about updating 'old' rrd files in rrdtool
today ... if you have to go this route you may want to add a
'rebase' option to rrdtool tune which lets you modify the last
update property in an existing rrd file.

I wonder though if you could not design your system in a way that
it does NOT break when it gets a request for 50'000 rrds by makeing
sure the process who tries to submit information does not have to
way for it to be actually stored back ...

> Thanks,
> -Ryan

Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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