[rrd-developers] rrd_update

[Praveen P]

Hi,

I had a question regarding the update of HW prediction
related parameters from rrd_update.

In rrd_hw.c, there is a comment saying that
DEVSEASONAL and DEVPREDICT arrays store the same
value:

line 260:

/* there really isn't any "update" here; the only
reason this information is stored separately from
DEVSEASONAL is to preserve deviation predictions for a
longer duration than one seasonal cycle. */

However we see that the values in these two arrays are
not exactly the same. The reason we came up on this is
that DEVSEASONAL seems to do a better job at storing
seasonal trends (based on the values we see) where as
DEVPREDICT is the one being used in the confidence
band calculation.

These are the last 20 values from an rrd file that we
have for these two arrays:


DEVSEASONAL - last 20 values:

<!-- 2006-09-18 13:54:00 EDT / 1158602040 --> <row><v>
6.7479187052e+02 </v></row>
<!-- 2006-09-18 13:56:00 EDT / 1158602160 --> <row><v>
6.8014805212e+02 </v></row>
<!-- 2006-09-18 13:58:00 EDT / 1158602280 --> <row><v>
7.1526216969e+02 </v></row>
<!-- 2006-09-18 14:00:00 EDT / 1158602400 --> <row><v>
7.3048319709e+02 </v></row>
<!-- 2006-09-18 14:02:00 EDT / 1158602520 --> <row><v>
6.6526793619e+02 </v></row>
<!-- 2006-09-18 14:04:00 EDT / 1158602640 --> <row><v>
6.4740017657e+02 </v></row>
<!-- 2006-09-18 14:06:00 EDT / 1158602760 --> <row><v>
6.6632103446e+02 </v></row>
<!-- 2006-09-18 14:08:00 EDT / 1158602880 --> <row><v>
6.8383080944e+02 </v></row>
<!-- 2006-09-18 14:10:00 EDT / 1158603000 --> <row><v>
6.6914494305e+02 </v></row>
<!-- 2006-09-18 14:12:00 EDT / 1158603120 --> <row><v>
6.4563236435e+02 </v></row>
<!-- 2006-09-18 14:14:00 EDT / 1158603240 --> <row><v>
7.2319254784e+02 </v></row>
<!-- 2006-09-18 14:16:00 EDT / 1158603360 --> <row><v>
6.9837722813e+02 </v></row>
<!-- 2006-09-18 14:18:00 EDT / 1158603480 --> <row><v>
6.4696817613e+02 </v></row>
<!-- 2006-09-18 14:20:00 EDT / 1158603600 --> <row><v>
6.5821443074e+02 </v></row>
<!-- 2006-09-18 14:22:00 EDT / 1158603720 --> <row><v>
6.4258822610e+02 </v></row>
<!-- 2006-09-18 14:24:00 EDT / 1158603840 --> <row><v>
6.5186322754e+02 </v></row>
<!-- 2006-09-18 14:26:00 EDT / 1158603960 --> <row><v>
6.9563451085e+02 </v></row>
<!-- 2006-09-18 14:28:00 EDT / 1158604080 --> <row><v>
6.7803150283e+02 </v></row>
<!-- 2006-09-18 14:30:00 EDT / 1158604200 --> <row><v>
6.6917753321e+02 </v></row>
<!-- 2006-09-18 14:32:00 EDT / 1158604320 --> <row><v>
6.7315462260e+02 </v></row>
<!-- 2006-09-18 14:34:00 EDT / 1158604440 --> <row><v>
6.6018746037e+02 </v></row>


DEVPREDICT - last 20 values:

<!-- 2006-09-18 13:54:00 EDT / 1158602040 --> <row><v>
7.1795098121e+02 </v></row>
<!-- 2006-09-18 13:56:00 EDT / 1158602160 --> <row><v>
7.1730298323e+02 </v></row>
<!-- 2006-09-18 13:58:00 EDT / 1158602280 --> <row><v>
7.1663328392e+02 </v></row>
<!-- 2006-09-18 14:00:00 EDT / 1158602400 --> <row><v>
7.1594734445e+02 </v></row>
<!-- 2006-09-18 14:02:00 EDT / 1158602520 --> <row><v>
7.1552220024e+02 </v></row>
<!-- 2006-09-18 14:04:00 EDT / 1158602640 --> <row><v>
7.1504178086e+02 </v></row>
<!-- 2006-09-18 14:06:00 EDT / 1158602760 --> <row><v>
7.1448710608e+02 </v></row>
<!-- 2006-09-18 14:08:00 EDT / 1158602880 --> <row><v>
7.1419651423e+02 </v></row>
<!-- 2006-09-18 14:10:00 EDT / 1158603000 --> <row><v>
7.1372565394e+02 </v></row>
<!-- 2006-09-18 14:12:00 EDT / 1158603120 --> <row><v>
7.1292603401e+02 </v></row>
<!-- 2006-09-18 14:14:00 EDT / 1158603240 --> <row><v>
7.1222275576e+02 </v></row>
<!-- 2006-09-18 14:16:00 EDT / 1158603360 --> <row><v>
7.1202793491e+02 </v></row>
<!-- 2006-09-18 14:18:00 EDT / 1158603480 --> <row><v>
7.1165836499e+02 </v></row>
<!-- 2006-09-18 14:20:00 EDT / 1158603600 --> <row><v>
7.1089053618e+02 </v></row>
<!-- 2006-09-18 14:22:00 EDT / 1158603720 --> <row><v>
7.1039830564e+02 </v></row>
<!-- 2006-09-18 14:24:00 EDT / 1158603840 --> <row><v>
7.1003574931e+02 </v></row>
<!-- 2006-09-18 14:26:00 EDT / 1158603960 --> <row><v>
7.0927786296e+02 </v></row>
<!-- 2006-09-18 14:28:00 EDT / 1158604080 --> <row><v>
7.0859560556e+02 </v></row>
<!-- 2006-09-18 14:30:00 EDT / 1158604200 --> <row><v>
7.0823369100e+02 </v></row>
<!-- 2006-09-18 14:32:00 EDT / 1158604320 --> <row><v>
7.0692641183e+02 </v></row>
<!-- 2006-09-18 14:34:00 EDT / 1158604440 --> <row><v>
7.0558473505e+02 </v></row>

Can someone please shed any light on this ?

Thanks in advance,
Praveen.



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