[OSRM-talk] Road speeds and profile restrictions

Patrick Niklaus patrick.niklaus at student.kit.edu
Thu Sep 17 21:37:08 UTC 2015

W.r.t. the pre-preprocessing you are correct.

> What is that extra power used for?

Including all sorts of external data sources. Also the logic in the
lua profiles is not just replaceable by simple key-value pairs, OSM
requires you to handle a lot of special cases.

> Presumably I could do the same for world preparation & routing? Have, perhaps a 100GB+ swap file, ideally on an SSD.

This will fall apart when you have some actual load pressure on the
system. We need random access to memory, which will create a lot of
page faults (== slow). Even an SSD is not even close to memory speed.

You have two options:
- split the datasets
- get a bigger server


On Thu, Sep 17, 2015 at 10:06 PM, Richard Marsden <winwaed at gmail.com> wrote:
> I've been evaluating OSRM, using it primarily as a library from C++.
> I believe I've determined the answer to most of the questions, but I'm
> also looking for confirmation.
> (I understand the reason for these constraints - the trade-off of
> speed vs flexibility)
> First, road speeds are set with 'profile.lua' at the osrm-extract
> stage. This filters out unnecessary roads (eg. foot paths for car
> routing), but also applies the road speeds.
> If I wish to change the speed profile, I need to regenerate the road
> network with osrm-extract and osrm-routed.
> Correct?
> If I wanted different speeds for the final distance/time calculations,
> I could use the returned route, and apply my own speed table according
> to the road type of each road segment. This would not, of course,
> change the route geometry is calculated.
> If I want a shortest route (distance optimized) instead of a quickest
> route (time optimized), I need to set all the road speeds to the same
> speed and regenerate the network. I.e. osrm does not directly support
> the concept of a "shortest route".
> The profile is provided with a LUA file. I had to look this one up :-)
> Looks a useful scripting language, but why is this profile a script
> file, and not a simple configuration file of constants (eg. key-value
> pairs)?
> Seems like an unnecessary complexity - I'd like to understand the
> perceived advantages. What is that extra power used for?
> Finally, the memory usage... I saw a reference to the server requiring
> 40GB of memory for pan-European routing. Presumably that could be
> offset with a large swap file(?)
> A large swap file has worked well when I was testing the US-South
> region on an 8GB machine.
> Presumably I could do the same for world preparation & routing? Have,
> perhaps a 100GB+ swap file, ideally on an SSD.
> Cheers,
> Richard Marsden
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