[OSRM-talk] Road speeds and profile restrictions

[Richard Marsden]

It is possible I've just managed to demonstrate this to myself.
osrm-prepare crashed out on the Europe-wide dataset  at the 90+%
complete level with 30GB swap (16GB real). For much of the run it
didn't go above about 15GB swap. Very slow of course - but that was to
be expected.

This continues to be a side / evaluation project, but I'm continuing
to investigate. Looks like the PC in question should be able to handle
most countries, but will balk at most continents, and the very largest
countries (e.g. the US). High-RAM hardware is relatively pricey, but
it is a possibility in the new year.

Looking at the individual pieces, next I'm going to look at the
profile.lua file. I've never used LUA before, but that is easy enough
to remedy with online tutorials and the various books that are
available. But what about the script that is used by OSRM? Is there
any documentation as to the variables and/or functions that are
expected?  And the tags used in OSM that the script is expected to
map?


Cheers,

Richard Marsden

On Thu, Sep 17, 2015 at 4:37 PM, Patrick Niklaus
<patrick.niklaus at student.kit.edu> wrote:
> 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 <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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