[SOLVED] CACTI vs. poller interval vs. rrd preset vs. cron

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eholz1
Cacti User
Posts: 129
Joined: Mon Oct 01, 2018 10:09 am

[SOLVED] CACTI vs. poller interval vs. rrd preset vs. cron

#1 Post by eholz1 » Mon Apr 08, 2019 10:17 am

Hello All,

I have a basic question on the relationship between the rrd data profile (aka preset)
the poller interval (I am using spine), and the cron interval.

I was able to eliminate all poller table not empty warnings by deleting all the rrd files (I have 421 devices.
I did this by choosing the System Default preset, using 5 min for cron poller run, and 5 minute for poller/spine run.

This created rrds, graphs without gaps, and stats are all green.

I assumed that when the poller is run (spine based, using 6 processes and 10 threads) it writes to the rrd
file(s) every 5 minutes. I figured that now I have good rrd files and graphs set, that I should be able
to change the poller interval (not cron) to 1 minute, thinking that instead of updating rrd files every 5 minutes,
it would just update the rrd file(s) every minute since the rrd profile remained unchanged. cron was unchanged, running
every 5 min.

I figured wrong! As soon as I changed the poller to 1 minute, and rebuilded the cache, I started getting "poller output table not empty"
warnings. When I changed the poller interval back to 5 minutes, all warnings went away.

Am I missing something here? I did try setting cron to every minute, but that still gave poller table warnings, etc.

I am open to any suggestions,

Thanks,
eholz1
Last edited by eholz1 on Tue May 07, 2019 6:15 pm, edited 1 time in total.

netniV
Cacti Guru User
Posts: 2691
Joined: Sun Aug 27, 2017 12:05 am

Re: Cacti poller vs. poller interval vs. rrd preset vs. cron

#2 Post by netniV » Mon Apr 15, 2019 7:22 am

You can't just update the profile to 1 minute because the RRD's contain a STEP which matches. You can't just change the RRD's STEP either because it has no idea what to do about the missing data or what data to summarise if less is needed.

For example, in your case, you are dropping from 5 minute (300 second) steps to 1 minute (60 second) steps. This means that for each step, there are four missing ones.

There is a script one of our guys was testing that allowed for adjustment of the steps, but that is currently being reviewed. It basically tries to fill in the missing data with an existing value. Not ideal but the best that it can do.

eholz1
Cacti User
Posts: 129
Joined: Mon Oct 01, 2018 10:09 am

Re: Cacti poller vs. poller interval vs. rrd preset vs. cron

#3 Post by eholz1 » Mon Apr 15, 2019 10:19 am

Hello netniV,

Excellent - actually, I am not sure I, as a user, would want to have a script that would
re-set the step - I also notice that the rrdtool "step" change does not work to change the step either.

It seems there are currently just two ways to change the step for an rrd of a given profile:
use a different profile (like 1 minute), see what the debug code puts out for the datasource,
and delete old or overwrite existing rrd file with the new step value using the new code (for one device),
OR - change the profile for an interface template, and delete all the rrd files for the device(s), and let them
rebuild.

Downside to deleting all, is data in file for previous step value is lost.

I found a workaround that gives me the capability to select the profile/preset by checking the box for the
Data Source Profile in a given data source template that allows overriding the default profile for that interface.

At least for me, I have discovered that I need to "plan ahead" if I want to use a profile other than "System Default" i.e.
is there any benefit to using the "High Collection Rate" profile, etc.

Thanks for reply,

eholz1

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