[Tilesathome] Proposal: New T at H Server structure

[Gerhard Schmidt]

Frederik Ramm schrieb:
> Hi,
> 
>> i have done quite some thinking lately how to speed up the tiles at home
>> upload. I've come up with an complete new structure of the server System.
> 
> There was a rather cool concept on the Wiki about a year ago where 
> we would distribute tiles using DNS, i.e. you would always find 
> the "responsible" server through DNS instead of through expensive 
> database lookups and HTTP redirects.

I haven't read the Proposal but as I read in an other Mail the logic
which server to use will be placed in the Map Java script code. breaking
all uses without JavaScript.

> My personal thinking though is that we don't need a complex system 
> like that because as soon as chrschmidt gets the new disks, everything
> is going to run smoothly again.

Until we hit the Wall again. Growing Traffic and growing T at H member
numbers will drive even the fastest server against the wall some day.

> A highly distributed concept, in my eyes, has one big drawback: We
> must assume that at any one time, a small percentage of tile servers
> will be down or slow. The usability of a map display is greatly
> reduced even if only one tile is missing. I would go so far as to say
> that a map consisting of 20 tiles, where one tile is a broken image,
> is a "failure". This means that if you get the tiles for one map
> display from 20 tile servers, then you have not a single point of
> failure, but 20 cascading single points of failure ;-)

Not at all. The TileServer can itself provide redundancy by forwarding
uploaded tiles to other servers (not all but 2, 3 or more based on the
number of TileServer available ) is there is more than one TileServer so
Together with an watchdog service we can reduce the possibility of
missing tiles to near Zero. With an intelligent redirector we can even
point to the nearest Tileserver having the requested tile. This will not
be in the first step but its an possibility for the Future

BTW the same Problem comes with the DNS distributed system as well.

I have written some Redirecting code for an Banner server which provides
redirect for about 4k Sites with 27k redirects per minute. This was 6
Years ago. And the redirect logic was far more complicated than the
redirects we have to do. For each tile there will be 1 or 2 database
request and some simple Math. The redirector will be the first part I
write than i will do some performance testing.

Regards
	Estartu

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