[OSM-dev] Slippy maps requesting ALL layers...

John McKerrell john at mckerrell.net
Mon May 7 09:54:40 BST 2007


On 7 May 2007, at 01:59, Frederik Ramm wrote:

> Hi,
>
>> As for the slippy map, wouldn't it be better to do this via round  
>> robin
>> DNS for mirrors?
>
> As far as I understood, distributing one user's request among multiple
> servers increases the chance of fast, parallel serving of tiles as the
> browser will normally have a limit of 4 (or so) parallel  
> connections to
> any one server, but allow 16 (or so) overall parallel connections.
>
I believe it varies by browser, but default Internet Explorer [1] is  
to allow 2 connections per domain, and up to 4 domains at once (or 6  
according to the linked article). So the ideal is to have requests  
split over 4(/6) domains to allow up to 8(/12) tiles loading per- 
page. Obviously there's no reason why these domains have to be  
different servers though so you can still have this multiplexing  
while having the surety of getting all your tiles from one server.
> Of course, having a lot of parallel servers also increases your  
> chances
> of having at least one that doesn't currently work ;-)

Indeed, but better than loading all your tiles from the one that  
doesn't currently work. I suppose we just need to make sure we don't  
have that "one", or offer direct connections to the servers as a  
backup, non-default layer.

John


[1] http://www.ajaxperformance.com/?p=33




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