# [rrd-users] Re: Problem on update

Alex van den Bogaerdt alex at ergens.op.HET.NET
Thu Jul 11 18:28:05 MEST 2002

```Chris Raymond wrote:

> As I see it, RRDtool is inserting BOGUS DATA.  In the example given,
> there is one real data point to insert, repeat, one.  It occurs at
> time 957481200.  This is on a 3600 second time update interval, but

[snip]

> I hope I've now made what I regard as a problem clear.

I think this is an expectation problem.

You expect to insert a data POINT.  This is not what RRDtool does.
RRDtool inserts, with one update, a range.  This is from the last
update to the current update.

Let's see if you and I agree on the situation.  The numbers don't

step time:  3600
heartbeat: 36000

T+1*3600:   value 1
T+2*3600:   value 2
T+3*3600:   value 3
<long time>
T+8*3600:   value 4

You expect the following to be inserted into RRDtool:

at T+1*3600:  1
at T+2*3600:  2
at T+3*3600:  3
at T+8*3600:  4

If above is *not* true then please try to rephrase your problem as
I clearly didn't understand in that case.  Also: stop reading now.

OK, you're still with me.  You expect the numbers to mean:

at T+1*3600:  the time range between T+0*3600 and T+1*3600
at T+2*3600:  the time range between T+1*3600 and T+2*3600
at T+3*3600:  the time range between T+2*3600 and T+3*3600
no updates    the time range between T+3*3600 and T+7*3600 --> NaN
at T+8*3600:  the time range between T+7*3600 and T+8*3600

Same question:  Are we still in sync?  If not, please rephrase.

OK, still here.

This is what I expect the numbers to mean:

at T+1*3600:  the time range between T+0*3600 and T+1*3600
at T+2*3600:  the time range between T+1*3600 and T+2*3600
at T+3*3600:  the time range between T+2*3600 and T+3*3600
at T+8*3600:  the time range between T+3*3600 and T+8*3600

Why is this last line different?  At time T+8 I enter a number.
RRDtool hasn't seen any update between T+3 and T+8.  Therefore
it *must* assume the update is valid throughout the entire time
range *unless* this is larger than heartbeat.  This is how the
tool is designed.  Since heartbeat is more than (8-3)*3600, the
update is valid *for the entire range*.

Again, I think you shouldn't be reading this because I think you
will have bailed out at the 2nd decision point.

cheers,
--
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