Speed difference: wget vs guix build

[Ricardo Wurmus]

Hi Guix,

a few weeks ago I noticed that the download of binary substitutes is
fairly slow when it is performed from within "guix build" compared with
wget:

    address@hidden:~] (557) $ time wget 
http://hydra.gnu.org/nar/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014
    --2015-05-06 08:20:38--  
http://hydra.gnu.org/nar/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014
    Resolving hydra.gnu.org (hydra.gnu.org)... 18.4.89.46
    Connecting to hydra.gnu.org (hydra.gnu.org)|18.4.89.46|:80... connected.
    HTTP request sent, awaiting response... 200 OK
    Length: unspecified [application/x-nix-archive]
    Saving to: ‘h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014.1’

        [                                         <=>                           
           ] 761,111,979 4.17MB/s

The speed ranges from ~4MB/s to 7MB/s with wget.
With guix build, however, I get much less on the same host:

    address@hidden:/localhome/rwurmus-tmp/guix] (557) $ ./pre-inst-env guix 
build texlive-texmf-2014
    The following file will be downloaded:
       /gnu/store/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014
    @ substituter-started 
/gnu/store/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014 
/usr/libexec/guix/substitute
    found valid signature for 
'/gnu/store/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014', from 
'http://hydra.gnu.org/nar/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014'
    downloading 
`/gnu/store/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014' (3391.2 MiB 
installed)...
    
http://hydra.gnu.org/nar/h1qjkg8bvcdb485q81lw5844szgywpg7-texlive-texmf-2014    
    124344.0 KiB transferred (321. KiB/s)

Is this expected?

~~ Ricardo