Pruning old data with histograms

[vladimiroltean]

Hi, I'm plotting the ping rtt with a command similar to this: sudo ping -A 172.15.0.3 -D | gawk '$4=="from" && $8~/time=/ && $9=="ms" {gsub(/[\[#\]]/, "", $1); gsub("time=", "", $8); print $1, $8; fflush()}' | feedgnuplot --domain --stream --lines --histogram 0 --binwidth 0.001 --histstyle freq--style 0 "linewidth 2"

This works as expected, but it clogs down at some point because it's keeping all old data. If I add "--xlen 10", gnuplot complains:

gnuplot> plot '-' using (histbin($2)):(1.0) smooth freq notitle linewidth 2
^ line 30480: all points y value undefined!

Am I misunderstanding the functionality? Is this a bug?

Thanks, Vladimir

[dkogan]

Vladimir Oltean notifications@github.com writes:

I'm plotting the ping rtt with a command similar to this:

sudo ping -A 172.15.0.3 -D | gawk '$4=="from" && $8~/time=/ && $9=="ms" {gsub(/[\[#\]]/, "", $1); gsub("time=", "", $8); print $1, $8; fflush()}' | feedgnuplot --domain --stream --lines --histogram 0 --binwidth 0.001 --histstyle freq--style 0 "linewidth 2"

This works as expected, but it clogs down at some point because it's keeping all old data. If I add "--xlen 10", gnuplot complains:

gnuplot> plot '-' using (histbin($2)):(1.0) smooth freq notitle linewidth 2 ^ line 30480: all points y value undefined!

Am I misunderstanding the functionality? Is this a bug?

Hi. I'm not totally sure what you're trying to do, so can't comment on whether it is a bug or not. You want a histogram of ping round-trip timings, and you want it to update as you get more data. Is that ALL you want, or you want other stuff overlaid on top of this histogram?

[vladimiroltean]

Yes, this is all I'm trying to achieve.

[dkogan]

Vladimir Oltean notifications@github.com writes:

Yes, this is all I'm trying to achieve.

I see. You were doing something more complex than what you needed. An updating histogram:

ping -A -D 8.8.8.8 | gawk '$4=="from" && $8~/time=/ && $9=="ms" {gsub(/[[#]]/, "", $1); gsub("time=", "", $8); print $8; fflush()}' | feedgnuplot --stream --histogram 0 --binwidth 0.1

Admittedly, the interaction of histograms with other options isn't good, and more error checking should be added. Currently there's no support of an "xlen" option to make a moving-window type plot for histograms. The invocation you gave should have given a useful error message or something. It would be good to add, but it's not there no. If you send me a patch, we can talk about it :)

[vladimiroltean]

Ok thanks for the answer. For the moment I may work around the issue by using an external program to generate the histograms.

[dkogan]

I made a few updates and this should now work with the sources in master. Look at the example in the manpage.

[vladimiroltean]

Thanks for taking the time to implement this. If I had to nitpick, I'd say that for histograms, --xmin and --xmax have a usefulness of their own, so they shouldn't be mutually exclusive with --xlen. For example, I'd like to be able to trim the histogram to only show rtt times between 0-20ms, and group all the out-of-range values in the first/last bin.

[dkogan]

You're not nitpicking at all. Thanks for the comment; I've pushed a fix. This is a set of features that I haven't been using together so there's untested logic, and I'm glad people are pointing out the deficiencies.