Bug#372712: apt: Shouldn't download pdiffs in all cases
Mike Hommey <mh@glandium.org> writes:
> On Sun, Jun 11, 2006 at 07:29:10PM +0200, Goswin von Brederlow <brederlo@informatik.uni-tuebingen.de> wrote:
>> Mike Hommey <mh+reportbug@glandium.org> writes:
>>
>> > Package: apt
>> > Version: 0.6.44
>> > Severity: wishlist
>> >
>> >
>> > When you don't apt-get update for a while, downloading all the pdiffs
>> > instead of the full file is actually much longer. There should be a limit
>> > of days without update after which apt would get the full file and not the
>> > pdiffs.
>>
>> There is a limit on the number of pdiff files available. With one file
>> per day that translates 1:1 into days.
>>
>> I don't get why it should be slower to download the diff files than
>> the full file unless you are using ftp. With http the index is fetched
>> (round trip 1) and then all needed diff files (round trip 2). So
>> downloading should never be slower.
>>
>> Does the patching take longer than downloading and bunziping the full
>> file on your system? I would think that even 10 days patching are
>> faster than bunziping the file but that is just a guess.
>
> The computer on which I got this shock had not been updated for a
> month, and yet, had to download all the diffs for more than 30 days !
>
> It seems the operation is hard to quantify in time since downloading and
> patching seems to be done sequencially (download, patch, download,
> patch, etc.).
>
> I don't know either what the speed indicator in apt gives then, but it's
> only giving 12KB/s where I can download full files at 700KB/s...
>
> Note that I use http, not ftp.
Maybe I'm wrong but I asked some apt maintainer before how the
downloading works. It should fetch the index, find all the patches
needed from the old Packages file to the current one and then fire off
all the donwlods together using the http keep-alive option. There
shouldn't be a delay between downloads. The patching should work in
parallel with downloads.
Anyway, that is the theory.
>> > PS: Is there a way to totally disable the pdiff stuff ? With decent
>> > bandwidth, it actually takes more times than downloading the full file...
>> > (Or is the goal to reduce the bandwitdh on the server side ?)
>>
>> The primary goal was to save all that download time every day on the
>> slow modem/dsl line. Probably nobody was thinking about GBit to the
>> next mirror and 2 weeks worth of diffs.
>>
>> Maybe the number of diffs kept is to big. Maybe not. To decide that
>> one needs more info about your (and lots of other peoples) network
>> structure and update seeds/traffic and then find a good compromise.
>
> I usually apt-get update every other day, and roughly download at
> 700KB/s.
But now you get 12K/s for a 20K file instead of 700K/s for a 4MB
file. Anyway, the speed indicator isn't good with small files.
> If you need more testing and numbers, tell me what you would like me to
> provide you, and I'll try to give you facts rather than impressions :)
>
> Mike
I will refrain from updating for a few days and test this too. I
normaly have a cron job that runs update + auto-clean every night. So
I never have to wait for it.
MfG
Goswin
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