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[205.151.56.104]) by smtp.gmail.com with ESMTPSA id h23sm3465738ila.81.2022.01.10.19.43.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Jan 2022 19:43:40 -0800 (PST) From: Maxim Cournoyer To: Ludovic =?utf-8?Q?Court=C3=A8s?= Subject: Re: bug#51472: substitute servers should be preferred according to their coverage rate References: <87k0hwa8ic.fsf@gmail.com> <874k8oknlj.fsf@gnu.org> Date: Mon, 10 Jan 2022 22:43:33 -0500 In-Reply-To: <874k8oknlj.fsf@gnu.org> ("Ludovic =?utf-8?Q?Court=C3=A8s=22'?= =?utf-8?Q?s?= message of "Sun, 07 Nov 2021 16:11:04 +0100") Message-ID: <87pmozndi2.fsf@gmail.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Score: 0.0 (/) X-Debbugs-Envelope-To: control Cc: 51472@debbugs.gnu.org, GNU Debbugs X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: debbugs-submit-bounces@debbugs.gnu.org Sender: "Debbugs-submit" X-Spam-Score: -1.0 (-) merge 48808 51472 thanks Hello Ludovic, Ludovic Court=C3=A8s writes: > Hi, > > Maxim Cournoyer skribis: > >> When using substitute servers discovery, I've noticed that if one of the >> substitute servers doesn't have any substitutes available, it'll keep >> getting tried instead of others, leading to a slide-show of substitutes >> updates such as: >> >> normalized load on machine '127.0.0.1' is 0.04 >> building /gnu/store/ajd0hx104702jpz2ycdwgrnyrv8jsp6d-xorg-server-21.1.0.= tar.xz.drv... >> process 9195 acquired build slot '/var/guix/offload/127.0.0.1:6666/1' >> normalized load on machine '127.0.0.1' is 0.04 >> building /gnu/store/49rqi3wpvdm5pv6in9pamzdvg0wscrl8-xorgproto-2021.5.dr= v... >> substitute: updating substitutes from 'http://192.168.10.102:80'... 0.= 0% >> substitute: updating substitutes from 'http://192.168.10.102:80'... 0.= 0% >> substitute: updating substitutes from 'http://192.168.10.102:80'... 0.= 0% >> substitute: updating substitutes from 'http://192.168.10.102:80'... 0.= 0% >> substitute: updating substitutes from 'http://192.168.10.102:80'... 0.= 0% > > We=E2=80=99d need to check why this particular server is checked repeated= ly. > The fact that it displays =E2=80=9C0.0%=E2=80=9D doesn=E2=80=99t mean tha= t the server lacks > substitutes, but that it does not reply to =E2=80=98GET /xyz.narinfo=E2= =80=99 requests, > for example because it=E2=80=99s off-line (see > .) > >> We should implement some scheme to prefer querying high-substitute >> servers first, instead of wasting time querying servers always failed >> queries; this would greatly improve performance when using substitute >> discovery for example combined with low coverage. > > There are several problems with that. First one is that you can=E2=80=99= t tell > what substitute coverage is until you=E2=80=99ve actually made those GET > requests. Second one is that substitute coverage varies and it=E2=80=99s= not an > absolute measure; for example, if a server provides substitutes for only > 0.1% of all the packages, but that=E2=80=99s precisely the 0.1% you care = about, > it=E2=80=99s more valuable than the one that has 99% of the packages but = lacks > those you want. > > There are other issues such as the fact that current semantics is to > respect the order of substitute URLs, which is presumably chosen by the > user according to their own criteria: download speed, bandwidth usage, > etc. > > I hope this makes sense! It does! I agree that it'd be tricky to get this right; makes me realize that my problem is probably due to #48808, and fixing that one would probably have avoided that bug report :-). I'm merging this one with 48808. Thank you! Maxim