[graphviz-interest] Performance - number of ranks

I am currently making quite large family tree graphs (1231 people in 342 marriages/familes).

I am using invisible "date" nodes to ensure that all people and marriages
are place in the correct vertical position on the diagram - I use rank=same
to lock each marriage or person to the relevant date node, whilst the date
nodes are simply joined by invisible sequential edges.

(very much as per graphs/directed/shells.gv)

However, dot on my (8Gb, i5-3210M CPU @ 2.50GHz) laptop,
takes 4 min 27 secs minutes, and has 300 dates/ranks.

If I quantise the dates to 5 year boundaries, I get 82 ranks,
and the dot processing time plummets to 17 seconds.

Is this the expected performance relationship?

(this only matters because I'm attempting to find nicer
graphs by permuting my initial person order in the file,
so the dot command is inside quite a large loop)

    BugBear
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