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Re: Debian mirror scripts

otto.wyss@orpatec.ch (Otto Wyss) writes:

> Goswin von Brederlow <brederlo@informatik.uni-tuebingen.de> wrote:
>> Otto Wyss <otto.wyss@orpatec.ch> writes:
>> reply (that is what I get roughly) to the server would waste 75 hours
>> on waiting for the initial three-way handshake for a connect. And
>> another 50 hours for the round-robin sending the name of a file and
>> getting the data.
> Did you messure this figures on a real Debian mirror or is it just what
> you think?

That is pure mathematics.

An initial tcp three way handshake has to travel tree times the
distance between me and the server. That is 150ms * 3 just to connect
and then one roundtrip to get the data flowing. Even if the 3rd packet
of the handshake is combined with data (not sure if that happens just
now) you still have to wait for the reply. So 4 or 5 times 150ms times
the number of files (~600000).

But it's not only math, I've tested this (not with that many files
obviously) for debmirror using ftp (one data connect per file), http
(one connect per file), http (keep-alive), rsync (1 file per connect)
and rsync (100 files per connect).

Http with keep-alive wins.

>> can use simple http/1.1. It's a win-win situation.
> Perfect go ahead. Even if DpartialMirror isn't developed further I use
> it almost daily and are quite happy with it. And I guess this won't
> change in the future.

If Debian starts shipping zsync checksum files in its mirror then
adapting to it should be trivial. Just add the Depends and replace the
rsync call with zsync. I just hope some ftp-master will.

> O. Wyss


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