95th Percentile Caculation for Aggregate (Last Month) is not accurate.

[iskandarbasman]

Describe the bug

95th Percentile Caculation for Aggregate (Last Month) is not accurate.

To Reproduce

Steps to reproduce the behavior:
Cacti Version 1.2.25

Created a test graph on by test cacti.

1. Using two existing 95th Percentile graphs.
2. Created a Aggregate 95th graph.
3. Used Preset: Last Month
4. See cacti 95th percentile calculated as 711.16 Mbits

Download the CSV export of the same graph data.
Noted that Cacti 95th value as in the graph. "Nth Percentile 711157443 |95:bits:0:aggregate_peak:2|"

Compared using the same data to calculate 95th Percentile.
Excel formula is getting : 502,123,554.75
Manual calculation using approximately 95% of total sample: 508305728.43

95th percentile by Excel and Manual calculation is close to each other.
95th percentile by Cacti is over by 200Mbits.

Attached the excel file:

Aggregate - test 19 mar 2024.xlsx

`
RRDtool Command:

/usr/bin/rrdtool graph -
--imgformat=PNG
--start='1708307700'
--end='1710813147'
--pango-markup
--title='Aggregate - test 19 mar 2024'
--vertical-label='bits per second'
--slope-mode
--base=1000
--height=200
--width=700
--rigid
--alt-autoscale-max
--lower-limit='0'
COMMENT:"From 2024-02-19 09:55:00 To 2024-03-19 09:52:27\c"
COMMENT:" \n"
--border 1
--slope-mode
--watermark 'Generated by SPTEL Cacti®'
DEF:a='/var/www/html/cacti/rra/1nete-ne20e-s1_traffic_in_2562.rrd':'traffic_in':LAST
DEF:b='/var/www/html/cacti/rra/1nete-ne20e-s1_traffic_in_2570.rrd':'traffic_in':LAST
DEF:c='/var/www/html/cacti/rra/1nete-ne20e-s1_traffic_in_2562.rrd':'traffic_out':LAST
DEF:d='/var/www/html/cacti/rra/1nete-ne20e-s1_traffic_in_2570.rrd':'traffic_out':LAST
CDEF:cdefa='a,8,'
CDEF:cdefe='b,8,'
CDEF:cdefi='c,8,'
CDEF:cdefbc='d,8,'
CDEF:cdefbj='TIME,1710806271,GT,a,a,UN,0,a,IF,IF,TIME,1710806271,GT,b,b,UN,0,b,IF,IF,+,8,'
CDEF:cdefce='TIME,1710806271,GT,c,c,UN,0,c,IF,IF,TIME,1710806271,GT,d,d,UN,0,d,IF,IF,+,8,'
AREA:cdefa#00CF007F:'1NETE-NE20E-S1'
GPRINT:cdefa:LAST:'Current:%8.2lf %s'
GPRINT:cdefa:AVERAGE:'Average:%8.2lf %s'
GPRINT:cdefa:MAX:'Maximum:%8.2lf %s\n'
AREA:cdefe#00CF007F:'1NETE-NE20E-S1':STACK
GPRINT:cdefe:LAST:'Current:%8.2lf %s'
GPRINT:cdefe:AVERAGE:'Average:%8.2lf %s'
GPRINT:cdefe:MAX:'Maximum:%8.2lf %s\n'
AREA:cdefi#002A97FF:'1NETE-NE20E-S1'
GPRINT:cdefi:LAST:'Current:%8.2lf %s'
GPRINT:cdefi:AVERAGE:'Average:%8.2lf %s'
GPRINT:cdefi:MAX:'Maximum:%8.2lf %s\n'
AREA:cdefbc#002A97FF:'1NETE-NE20E-S1':STACK
GPRINT:cdefbc:LAST:'Current:%8.2lf %s'
GPRINT:cdefbc:AVERAGE:'Average:%8.2lf %s'
GPRINT:cdefbc:MAX:'Maximum:%8.2lf %s\n'
COMMENT:' \n'
COMMENT:' \n'
COMMENT:' \n'
LINE1:cdefbj#00CF00FF:
LINE1:cdefbj#00CF007F:'Total '
GPRINT:cdefbj:LAST:'Current:%8.2lf %s'
GPRINT:cdefbj:AVERAGE:'Average:%8.2lf %s'
GPRINT:cdefbj:MAX:'Maximum:%8.2lf %s\n'
LINE1:cdefce#002A97FF:
LINE1:cdefce#002A977F:'Total '
GPRINT:cdefce:LAST:'Current:%8.2lf %s'
GPRINT:cdefce:AVERAGE:'Average:%8.2lf %s'
GPRINT:cdefce:MAX:'Maximum:%8.2lf %s\n'
COMMENT:' \n'
HRULE:711157442.95#FF0000FF:'95th Percentile'
COMMENT:'(711.16 mbit in+out)'

RRDtool Command lengths = 2253 characters.
RRDtool Says:
OK
`

[aliuzzz]

1.2.26 is ok

[iskandarbasman]

I saw there was a major bug fix aggregate graphs and percentiles for 1.2.26.
So far trying it out has been positive (95th percentile value is more accurate) but its seems i have to recreate the aggregate graphs for it to use this new N-th percentile template ?

Old Graph

New Graph

[TheWitness]

We will table this discussion for 1.2.27. We will restart the conversation after release.