pipelining on archive.u.c aborts after 101 packages

Bug #1794957 reported by Julian Andres Klode on 2018-09-28
10
This bug affects 1 person
Affects Status Importance Assigned to Milestone
apt (Ubuntu)
Undecided
Unassigned
Xenial
Undecided
Unassigned
Bionic
Undecided
Unassigned

Bug Description

[Impact]
Downloading many packages on archive.ubuntu.com or some other mirrors seems to close the connection after every 100 or so packages. APT prior to 1.7.0~rc1 (commit df696650b7a8c58bbd92e0e1619e956f21010a96), treats a connection closure with a 200 response as meaning that the server does not support pipelining, hence disabling it for any further downloads.

With high speed connections at higher latency, this can cause a severe reduction in usable bandwidth. For example, I saw speeds drop from 40 MB/s to 15 MB/s due to this.

The fix ensures that we continue pipelining if the previous connection to the server successfully retrieved at least 3 files with pipelining enabled.

[Test case]
Pick a package that would cause a large number (200/300 packages of packages to be installed). I used plasma-desktop and xubuntu-desktop, for example. Run apt install -d $package. Ensure that after the first 101 packages the progress does not slow down - you should not see a lot "working" in the progress output. The speed should be substantially higher.

Don't run in a container setup by cloud-init, as cloud-init disables pipelining; or remove /etc/apt/apt.conf.d/90cloud-init-pipelining (see bug 1794982).

Requirements:
* High speed, medium-high latency connection (e.g. 400 Mbit/s at 30 ms RTT is enough); or just increase latency, e.g.
   sudo tc qdisc add dev wlp61s0 root netem delay 300ms
 until you see the slow down
* Not a terribly slow CPU, as we'd get slowed down by hashing otherwise

[Regression potential]
This fix is isolated to code enabling/disabling pipelining on subsequent connections. It could cause more pipelining to be tried on servers who are not particularly good at it, but can deal with 3 items correctly.

Changed in apt (Ubuntu):
status: New → Fix Released
Changed in apt (Ubuntu Xenial):
status: New → Triaged
Changed in apt (Ubuntu Bionic):
status: New → Triaged
description: updated

Hello Julian, or anyone else affected,

Accepted apt into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/1.6.5 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Changed in apt (Ubuntu Bionic):
status: Triaged → Fix Committed
tags: added: verification-needed verification-needed-bionic
Łukasz Zemczak (sil2100) wrote :

Hello Julian, or anyone else affected,

Accepted apt into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/1.2.28 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Changed in apt (Ubuntu Xenial):
status: Triaged → Fix Committed
tags: added: verification-needed-xenial
Brian Murray (brian-murray) wrote :

Hello Julian, or anyone else affected,

Accepted apt into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/1.2.29 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

Brian Murray (brian-murray) wrote :

Hello Julian, or anyone else affected,

Accepted apt into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/apt/1.6.6 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

description: updated
Julian Andres Klode (juliank) wrote :

Here is a short graphical comparison of before/after in the bionic SRU in a container. I modified the container's network bridge to add 300ms delay using

sudo tc qdisc add dev lxdbr0 root netem delay 300ms

which made things quite more visible on a slower 12 Mbit/s connection.

I could clearly see that _without_ the 1.6.6 SRU, speed dropped a lot after the first 100 (101?) packages were fetched, you could see in the progress that it fetched one file and then started fetching the next one.

In contrast, with the SRU installed, progress sometimes shows lines with multiple files very quickly; i.e. it drains the entire pipe of 10 items in what feels like one update of the progress output.

You can also see this in the pictures: In the old graph, network speed has a sudden drop in the middle; in the second picture (which was running a bit longer, so it starts more on the left), you see that performance can be sustained.

Julian Andres Klode (juliank) wrote :

Same for xenial; 1.2.27 shows the symptoms, and the 1.2.29 SRU fixes them. Not going to attach more images or text as it basically looks identical.

tags: added: verification-done verification-done-bionic verification-done-xenial
removed: verification-needed verification-needed-bionic verification-needed-xenial
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