Comment 16 for bug 1396787

Tested with 1.1ubuntu1.18.04.7~16.04.1:

On the autopkgtest infrastructure u-u runs for 20s when all packages are installed from xenial-security but none from xenial-updates:

https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-xenial/xenial/amd64/u/unattended-upgrades/20181213_182038_2962e@/log.gz
...
Starting unattended upgrades script
Allowed origins are: o=Ubuntu,a=xenial, o=Ubuntu,a=xenial-security, o=UbuntuESM,a=xenial
Packages that will be upgraded:
19.18user 1.17system 0:20.53elapsed 99%CPU (0avgtext+0avgdata 77720maxresident)k
0inputs+123512outputs (0major+38986minor)pagefaults 0swaps
...

On a 2012 MacBook Air inside a KVM qemu vm autopkgtest runner it is ~8s:
...
adt-2.log-Allowed origins are: o=Ubuntu,a=xenial, o=Ubuntu,a=xenial-security, o=UbuntuESM,a=xenial
adt-2.log-Packages that will be upgraded:
adt-2.log:7.64user 0.31system 0:08.00elapsed 99%CPU (0avgtext+0avgdata 76516maxresident)k
..

This is basically the same speed as with 0.90ubuntu0.10.
There is a 12% speed regression when testing in qemu with kvm on a 19.04 host:

...
adt-1549534420.log-Allowed origins are: o=Ubuntu,a=xenial, o=Ubuntu,a=xenial-security, o=UbuntuESM,a=xenial
adt-1549534420.log-Packages that will be upgraded:
adt-1549534420.log:6.72user 0.30system 0:07.07elapsed 99%CPU (0avgtext+0avgdata 77812maxresident)k
...
vs.
..
adt-2.log-Allowed origins are: o=Ubuntu,a=xenial, o=Ubuntu,a=xenial-security, o=UbuntuESM,a=xenial
adt-2.log-Packages that will be upgraded:
adt-2.log:7.64user 0.31system 0:08.00elapsed 99%CPU (0avgtext+0avgdata 76516maxresident)k
...

Or a 24% speedup with a smaller set of upgradable packages measured in two 16.04 lxc containers running on the same 19.04 development system:

ii unattended-upgrades 0.90ubuntu0.10 all automatic installation of security upgrades

# for i in $(seq 5); do time unattended-upgrade --dry-run; done

real 0m4.326s
user 0m4.245s
sys 0m0.043s

real 0m4.309s
user 0m4.239s
sys 0m0.070s
...
# apt list --upgradable
Listing... Done
cloud-init/xenial-proposed 18.5-21-g8ee294d5-0ubuntu1~16.04.1 all [upgradable from: 18.4-0ubuntu1~16.04.2]
kmod/xenial-proposed 22-1ubuntu5.2 amd64 [upgradable from: 22-1ubuntu5.1]
libc-bin/xenial-proposed 2.23-0ubuntu11 amd64 [upgradable from: 2.23-0ubuntu10]
libc6/xenial-proposed 2.23-0ubuntu11 amd64 [upgradable from: 2.23-0ubuntu10]
libkmod2/xenial-proposed 22-1ubuntu5.2 amd64 [upgradable from: 22-1ubuntu5.1]
locales/xenial-proposed 2.23-0ubuntu11 all [upgradable from: 2.23-0ubuntu10]
multiarch-support/xenial-proposed 2.23-0ubuntu11 amd64 [upgradable from: 2.23-0ubuntu10]
python-apt-common/xenial-proposed 1.1.0~beta1ubuntu0.16.04.3 all [upgradable from: 1.1.0~beta1ubuntu0.16.04.2]
python3-apt/xenial-proposed 1.1.0~beta1ubuntu0.16.04.3 amd64 [upgradable from: 1.1.0~beta1ubuntu0.16.04.2]
snapd/xenial-proposed 2.37.1 amd64 [upgradable from: 2.34.2]
ubuntu-core-launcher/xenial-proposed 2.37.1 amd64 [upgradable from: 2.34.2]
unattended-upgrades/xenial-proposed 1.1ubuntu1.18.04.7~16.04.1 all [upgradable from: 0.90ubuntu0.10]
#

vs.

ii unattended-upgrades 1.1ubuntu1.18.04.7~16.04.1 all automatic installation of security upgrades

# for i in $(seq 5); do time unattended-upgrade --dry-run; done

real 0m3.269s
user 0m3.194s
sys 0m0.076s

real 0m3.277s
user 0m3.135s
sys 0m0.115s
...
root@x-uu-ref:~# apt list --upgradable
Listing... Done
cloud-init/xenial-proposed 18.5-21-g8ee294d5-0ubuntu1~16.04.1 all [upgradable from: 18.4-0ubuntu1~16.04.2]
kmod/xenial-proposed 22-1ubuntu5.2 amd64 [upgradable from: 22-1ubuntu5.1]
libc-bin/xenial-proposed 2.23-0ubuntu11 amd64 [upgradable from: 2.23-0ubuntu10]
libc6/xenial-proposed 2.23-0ubuntu11 amd64 [upgradable from: 2.23-0ubuntu10]
libkmod2/xenial-proposed 22-1ubuntu5.2 amd64 [upgradable from: 22-1ubuntu5.1]
locales/xenial-proposed 2.23-0ubuntu11 all [upgradable from: 2.23-0ubuntu10]
multiarch-support/xenial-proposed 2.23-0ubuntu11 amd64 [upgradable from: 2.23-0ubuntu10]
python-apt-common/xenial-proposed 1.1.0~beta1ubuntu0.16.04.3 all [upgradable from: 1.1.0~beta1ubuntu0.16.04.2]
snapd/xenial-proposed 2.37.1 amd64 [upgradable from: 2.34.2]
ubuntu-core-launcher/xenial-proposed 2.37.1 amd64 [upgradable from: 2.34.2]
root@x-uu-ref:~#