[OSRM-talk] Road speeds and profile restrictions

Richard Marsden winwaed at gmail.com
Fri Sep 18 02:32:54 UTC 2015


Thanks Steve,

Fair enough!

Richard

On Thu, Sep 17, 2015 at 8:20 PM, Stephen Woodbridge
<woodbri at swoodbridge.com> wrote:
> Richard,
>
> I have already imbedded OSRM into a C++ application and in fact wrapped that
> application into a postgresql database extension. I my case I only need data
> for a city but I was making literally billions of calls to osrm.
>
> As Patrick said, OSRM makes random access calls to memory and there are a
> lot of variables that come into play like how well the data is clustered in
> memory pages, how many page faults you hit, etc. For your specific use case
> no one will have a good answer for you and you really need to do some
> performance testing using the product the way you intend it to be used and
> see what the performance issues are. Maybe you use case is fine. The OSRM
> public service uses lots of memory because it has to support multiple random
> requests anywhere in the world and it can not afford to get stuck page in
> swap. Using swap and an SSD might be fine in your application, and may be it
> won't, but we do not have enough information to consider the problem more
> than to give the standard answer - more memory is faster more swapping is
> slower.
>
> -Steve
>
>
>
>
> On 9/17/2015 8:45 PM, Richard Marsden wrote:
>>
>> Thanks for the quick reply Patrick.
>>
>>> 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
>>
>>
>>
>> I would imagine that is the case for the standard http server. I was
>> thinking of using it as a linked library from a C++ program. Splitting
>> the datasets by continent is a possibility though.
>>
>> (writing a C# interface was another thought, but that would be a
>> different use case and definitely with smaller datasets)
>>
>> Cheers,
>>
>> Richard
>>
>>
>>
>>
>> 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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>>>> https://lists.openstreetmap.org/listinfo/osrm-talk
>>>
>>>
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