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 Cheers, Patrick On Thu, Sep 17, 2015 at 10:06 PM, Richard Marsden <[email protected]> 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 > > _______________________________________________ > OSRM-talk mailing list > [email protected] > https://lists.openstreetmap.org/listinfo/osrm-talk _______________________________________________ OSRM-talk mailing list [email protected] https://lists.openstreetmap.org/listinfo/osrm-talk
