[Xymon] Gaps in graphs

[Jeremy Laidman]

On Thu, 4 Mar 2021 at 21:44, Carl Melgaard <Carl.Melgaard at stab.rm.dk> wrote:

> Hi,
>
>
>
> How serious is gaps in graphs – for instance disk-graphs etc. Is a gap the
> same as potential missing alerting on events?
>
>
>
> Regards,
>
>
>
> Carl Melgaard
>

Yes, usually gaps in graphs are caused by missing data points. In the case
of the disk graph, this is usually caused by missing client data messages
that are not being sent from host to Xymon server, for some reason - such
as stopping the Xymon client at just the wrong time. It's also possible
that client data messages are not being sent in a timely manner - if two
data points are fed into RRD within the same 5-minute interval, the second
one is ignored, and then the next 5-minute interval with have no data point.

One unlikely cause of missing graphs is that the client data message is
being truncated. If the disk stats are after the point of truncation, then
there are no data points to add to the RRD file, so you'll see a gap. I
would check your xymond.log file for messages like "Oversize data/client
msg from 10.1.1.1 truncated n=<msgsize>, limit <msglimit>). If disk graphs
are affected by a section earlier in the message, it's likely that other
graphs are also affected by this - the [df] section is followed by [free]
(memor), then [ifconfig] and all the other sections used for network stats.
Perhaps scan down the graphs on the trends page looking for similar gaps.

I've seen client data message truncation cause missing data points, but,
it's actually unlikely this is the cause of your problem. All of the client
data sections that are likely to cause truncation are after the sections
that are used for the standard graphs (including disk). But it couldn't
hurt to check. Message limit defaults can be changed in the xymonserver.cfg
file - search the man page for MAXMSG_CLIENT for more details.

If the cause is something else, I suspect you'll still find clues in your
xymond.log file. But also check rrd-data.log and rrd-status.log.

J
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