Fedora Unity release

Bill Davidsen davidsen at tmr.com
Sun Feb 17 14:55:55 UTC 2008


Robert L Cochran wrote:
> I use jigdo myself and like the way it pulls packages from a list of
> servers, so that no one server is stressed with a long download
> connection that might be dropped or which might be so busy you can't log
> onto it.
> 
> The really bad thing about jigdo is that it isn't smart enough by
> default to notice that one or more servers consistently have connection
> problems, and it keeps hitting them again and again in round-robin
> fashion retrying the connection, and that in turn wastes a lot of time.
> Jigdo should drop a server after two different sets of two attempts per
> set which still fail to connect, and then go on to the next server in
> the list.

I would say there are a number of problems with the whole concept.


1 - The downloads do not run in parallel, so the time to download is the 
sum of all the download times, rather than the sum divided by the number 
of servers.

2 - any slow servers get totally hammered. If a server is running into 
bandwidth limits, new requests come in before the first ones finish, 
raising the load and further reducing bandwidth to any given client. 
With bittorrent the number of data providers goes up as the load goes 
up, and because the client will pull more data from the faster servers 
the average transfer rate to the client is higher.

3 - there doesn't seem to be any benefit to the server for jigdo vs. 
bittorrent, the load changes from a steady light load to a bursty heavy 
load per client request. It's not obvious that the same servers serving 
bittorrent would be any more loaded under any number of clients, but the 
bandwidth needed would be reduced under heavy load as clients provide 
part of the outgoing bandwidth.


That's my read on it, when a release first comes out the servers get 
hammered harder with jigdo than bittorrent. The sole advantage of jigdo 
is use of protocols which are more likely to be permitted through 
firewalls, and conceptually allowing a server to have only part of the 
larger image taking up disk space. I doubt that any machine which can't 
hold the whole image should be a server anyway, that's just my take on 
it, opinion rather than fact.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot




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