Hi all,
I recently started using Ganglia on our Mac Mini cluster and I noticed that
the graphs are resized from their native size so that they fit the
templates. This didn't make a lot of sense to me, so I edited the system so
that the images returned by graph.php calls are used as-is. I added two
variables "sx" and "sy" which are passed in the graph.php call specifying
the desired width and height of the output image. This approach means that,
at least for the image calls which are fully specified from the templates,
the dimensions can be specified in the template and needn't be worried about
anywhere else. When I made this modification I discovered that the width
and height that rrdgraph takes are actually the dimensions of the canvas
(the inside box that the actual graph is plotted on), and they don't include
the outer box. Rrdgraph does provide a way to get the final image's
dimensions (--imginfo), but it is not possible to use it while also using
the standard output mode (which is what the graph.php call does). So I
added a second call in graph.php which writes to /dev/null and simply parses
the output dimensions and adjusts the dimensions given to the second call by
the amount necessary to make the final dimensions match the "sx" and "sy"
variables. Since the "z" variable is obsolete but was still used to change
the graph style slightly for the host graphs, I changed it to a "formtype"
variable ("f") with values of "compact" or "normal." Oh, I also changed the
images to PNG instead of GIF since the rrdtool documentation says that PNGs
are generated as fast or faster and are as small or smaller than GIFs.
Here's the code:
#
# Generate the rrdtool graph command.
#
if ($formtype != "compact")
{
$command = RRDTOOL . " graph /dev/null --start $start --end $end
".
"--width $width --height $height $upper_limit $lower_limit ".
"--title '$title' $vertical_label $extras $background ".
" --imgformat 'PNG' --imginfo '%s\n%lu %lu' ".
$series;
$imginfo = exec($command);
$dims = explode(" ", $imginfo);
$width = $width - ($dims[0]-$width);
$height = $height - ($dims[1]-$height);
}
$command = RRDTOOL . " graph - --start $start --end $end ".
"--width $width --height $height $upper_limit $lower_limit ".
"--title '$title' $vertical_label $extras $background ".
#"--imgformat 'PNG' ".
"--step 5 ".
$series;
There are a few problems with this approach: 1) /dev/null is platform
specific (are there other parts of Ganglia that are already platform
specific so that this isn't such an issue?); 2) if the layout of the graph's
legend changes when the dimensions are adjusted, the adjustments won't be
correct, and I'm not sure what the best approach is to fix this. Let me
know what you guys think about this approach. If it's satisfactory, I'll
submit the changes to the repository.
Also, has there been any discussion about using SVG instead of raster
formats for the graph output? It would introduce serious user agent
compatibility considerations, but it would provide quite a lot of potential
benefits (interactivity, anyone?). Rrdtool's SVG output would need to be
improved, though.
Thanks,
Matt Chambers
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