[rrd-users] Average consolidation bug ?

[Ralf Kruedewagen]

Hi,
I have a strange problem with RRDTool's consolidation function.

My measurements and parameters:
I have some measurements of success rates, which are set up to store
either 0 (no success) or 100 (success) to a RRDTool database.

STEP=900 (=15 min.)
HEARTBEAT=3600
DS-Type: GAUGE
RRDTool version 1.2.12

The data series I have stored to RRD is:
20060328 19:00:44       100
20060328 19:03:11       100
20060328 19:05:48       100
20060328 19:08:17       100
20060328 19:10:34       100
20060328 19:21:47       0
20060328 19:23:05       100
20060328 19:25:21       100
20060328 19:27:41       100
20060328 19:30:13       100
20060328 19:32:42       100
20060328 19:35:05       100

During 19:00 - 19:15 I had 5 successful samples, which were all
stored to RRD with value=100. Then at 19:21:47 the only error
occured and I stored a 0 to the database. RRDTool is then averaging
the success rate between 19:00 and 19:15 to 70.44:

[1143566100]RRA[AVERAGE][1]DS[success] = 7.0444444444e+01

Question 1)
How does RRDTool handle the consolidation here. 70 might be the
result of averaging the values from 19:21 for 900 seconds in the
past. If so, this is quite strange. Why are the results at 19:00,
19:03 and 19:05 not considered here ? I would expect a bit higher
average here.

At 19:30 RRDTool does again consolidate. But now the average is
only 54.77:

[1143567000]RRA[AVERAGE][1]DS[success] = 5.4777777778e+01

Question 2)
This is really strange now. I would expect an average of at least 75.
For my perspective this could be a bug. Why do I have an average of
70 and 55 for only one unsuccessful sample ????? I have 9 samples
between 19:00 and 19:30 and only one with a value of 0.

See also image attached, showing the results.

Maybe someone can explain a bit how RRDTool works here or if this is
a bug. Is there any good doc that explains how RRDTool consolidates
in detail ?

Cheers
Ralf


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