[mapguide-users] Guestion about speedup mapguide, diferent domainname to mapagent.fcgi.

[Paul Spencer]

I'll weigh in here :)

There was a recent thread on the ka-map list that is relevant to this  
discussion.  The poster claimed (I didn't verify it, but it seems  
correct) that tile sources in google maps all point to a variety of  
server names like:

m0.google.com
m1.google.com
m2.google.com
m3.google.com

and that each of these resolves to the same IP.  This is being done  
to provide more simultaneous connections than a default configuration  
of a browser would make - and it works very well.

The poster also provided a patch for ka-Map that implemented a simple  
round-robin server picker from an array of available servers for the  
tile code.  He claimed substantial improvement in apparent tile  
loading speed because more tiles loaded simultaneously.

I am going to be implementing his patch in ka-Map (in a slightly  
different way, but the same concept) because I need this for a  
current client.  I can report back on our success.

On a side note, OpenLayers already has the capability to specify an  
array of servers as a tile source for a layer.

Finally, we've been looking closely at optimizing kaMap performance  
for our client.  Part of this has involved reorganizing how the tiles  
are physically cached on disk to avoid problems with having too many  
entries per directory.  The other part was using the web server  
directly to serve tiles.  This means the client is aware of the  
server cache structure and the cache is directly exposed through the  
web server.  A 404 error handler is used to trigger tile generation  
when the cache does not contain a particular set of tiles.

Also, we switched from Apache to lighttpd as it is quite a bit faster  
at serving files.  There are also other web servers that are faster  
than Apache.

One of the problems I see with MapGuide's tile caching mechanism is  
that the tiles are not stored at the web tier, but rather at the  
server.  This implies that you must invoke some process in addition  
to the web server and wait for the transfer between the server and  
the web tier, even if they are on the same machine.  This would be a  
very difficult problem to solve in MapGuide, though, because the  
architecture allows you to set up multiple web tiers and multiple  
servers in the back end - I don't envy Bob this particular problem :)

Cheers

Paul

On 28-Feb-07, at 6:52 PM, Jason Birch wrote:

> Hi Trevor,
>
> There are two points here:
>
> - If the tiles were served directly from disk by apache (or IIS), you
> will likely better performance than through the tileservice, primarily
> because there will be less CPU overhead.  However, the recent changes
> there (caching maps, etc).
>
> - From the client level, they only have two pipes to receive those  
> tiles
> through, so even if you're serving 100 tiles per second, the client is
> only going to be able to download two at a time.  They have to pull  
> down
> all of the HTML and JS code through the same pipes, so initial load  
> time
> can be a killer at high resolution (more tiles to fill the screen).
>
> On a somewhat-related note, TileCache looks interesting:
> http://labs.metacarta.com/wms-c/
>
> Jason
>
>
> -----Original Message-----
> From: Trevor Wekel
> Subject: RE: [mapguide-users] Guestion about speedup mapguide,diferent
> domainname to mapagent.fcgi.
>
> I don't know how much network latency and bandwidth affect tile  
> serving
> speeds.  However, I have had very good tile serving performance over a
> LAN with recent builds of MapGuide.  I have seen tile serving   
> speeds in
> excess of 100 tiles per second over a gigabit ethernet link with  
> current
> hardware (Pentium D 820).
>
> It would also be worthwhile to monitor CPU usage on the server while
> tiles are being served.  I suspect the bottleneck is CPU and not  
> network
> latency or bandwidth.
> _______________________________________________
> mapguide-users mailing list
> mapguide-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapguide-users

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|Paul Spencer                          pspencer at dmsolutions.ca    |
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|Chief Technology Officer                                         |
|DM Solutions Group Inc                http://www.dmsolutions.ca/ |
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