[rrd-users] Re: inserting historical data to rrdtool
don.baarda at baesystems.com
Fri Aug 18 09:06:46 MEST 2000
> -----Original Message-----
> From: Adam Treister [SMTP:adam at treestar.com]
> Sent: Friday, August 18, 2000 4:27 PM
> To: RRD users
> Cc: adam at treestar.com
> Subject: [rrd-users] Re: inserting historical data to rrdtool
> ----->>> On 17-Aug-2000, Alex van den Bogaerdt wrote:
> > RRDtool needs its input in a sequential order. You cannot go
> > back in time to insert values or to replace values.
> If rrdtool preallocates the whole db when its created, seems like it'd be
> simple to allow it to insert the data in any order. When the data is
> coming from disperse sources or overlaps between files, this would make
> life easier. Not a whole lot, but a little.
The problem is that rrd does adjustments to the data based on
previous samples before accumulating and storing info into the database. It
adjusts slightly miss-timed samples by calculated adjusted values using the
previous sample (and it's time). It can fill in multiple entries from a
single sample if the time-gap since the last sample spans multiple entries
(and heartbeat is set high enough). An unknown sample results in unknown
entries before and after that sample. etc. etc.
For RRD to get this right, it needs to know _all_ the samples taken
immediately before, immediately after, and during a recorded entry. If the
samples are not time-ordered, how can it know when it has all the samples
needed to fill in any entry?
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