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Subject: bug#51472: substitute servers should be preferred according to their coverage rate
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Hello,

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:

--8<---------------cut here---------------start------------->8---
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.drv...
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%
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%
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%
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%
substitute: updating substitutes from 'http://192.168.10.102:80'...   0.0%
substitute: updating substitutes from 'http://127.0.0.1:8080'... 100.0%
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%
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://127.0.0.1:8080'... 100.0%
substitute: updating substitutes from 'http://192.168.10.102:80'...   0.0%
--8<---------------cut here---------------end--------------->8---

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.

Thanks!

Maxim

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From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: Maxim Cournoyer <maxim.cournoyer@HIDDEN>
Subject: bug#51472: Acknowledgement (substitute servers should be
 preferred according to their coverage rate)
Message-ID: <handler.51472.B.163547327313895.ack <at> debbugs.gnu.org>
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Date: Fri, 29 Oct 2021 02:08:02 +0000

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Subject: bug#51472: substitute servers should be preferred according to their coverage rate
Resent-From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
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To: Maxim Cournoyer <maxim.cournoyer@HIDDEN>
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From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
References: <87k0hwa8ic.fsf@HIDDEN>
Date: Sun, 07 Nov 2021 16:11:04 +0100
In-Reply-To: <87k0hwa8ic.fsf@HIDDEN> (Maxim Cournoyer's message of "Thu, 28
 Oct 2021 22:07:39 -0400")
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Hi,

Maxim Cournoyer <maxim.cournoyer@HIDDEN> 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.t=
ar.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.drv=
...
> 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 repeatedly.
The fact that it displays =E2=80=9C0.0%=E2=80=9D doesn=E2=80=99t mean that =
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
<https://issues.guix.gnu.org/48808>.)

> 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=99t =
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 n=
ot 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 ab=
out,
it=E2=80=99s more valuable than the one that has 99% of the packages but la=
cks
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!

Ludo=E2=80=99.

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Subject: bug#51472: substitute servers should be preferred according to their coverage rate
Resent-From: Maxim Cournoyer <maxim.cournoyer@HIDDEN>
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Cc: 51472 <at> debbugs.gnu.org, GNU Debbugs <control <at> debbugs.gnu.org>
From: Maxim Cournoyer <maxim.cournoyer@HIDDEN>
References: <87k0hwa8ic.fsf@HIDDEN> <874k8oknlj.fsf@HIDDEN>
Date: Mon, 10 Jan 2022 22:43:33 -0500
In-Reply-To: <874k8oknlj.fsf@HIDDEN> ("Ludovic =?UTF-8?Q?Court=C3=A8s?="'s message of "Sun, 07 Nov 2021 16:11:04 +0100")
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merge 48808 51472
thanks

Hello Ludovic,

Ludovic Court=C3=A8s <ludo@HIDDEN> writes:

> Hi,
>
> Maxim Cournoyer <maxim.cournoyer@HIDDEN> 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
> <https://issues.guix.gnu.org/48808>.)
>
>> 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

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From: Maxim Cournoyer <maxim.cournoyer@HIDDEN>
To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@HIDDEN>
Subject: Re: bug#51472: substitute servers should be preferred according to
 their coverage rate
References: <87k0hwa8ic.fsf@HIDDEN> <874k8oknlj.fsf@HIDDEN>
Date: Mon, 10 Jan 2022 22:43:33 -0500
In-Reply-To: <874k8oknlj.fsf@HIDDEN> ("Ludovic =?utf-8?Q?Court=C3=A8s=22'?=
 =?utf-8?Q?s?= message of "Sun, 07 Nov 2021 16:11:04 +0100")
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merge 48808 51472
thanks

Hello Ludovic,

Ludovic Court=C3=A8s <ludo@HIDDEN> writes:

> Hi,
>
> Maxim Cournoyer <maxim.cournoyer@HIDDEN> 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
> <https://issues.guix.gnu.org/48808>.)
>
>> 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

Last modified: Tue, 11 Jan 2022 03:45:01 UTC

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