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I just updated from 11.04 to Ubuntu 12.04 by doing a fresh install.

I installed apt-cacher-ng and notice something strange about it. It's always downloading an index file (Packages.gz) even though the file exists in the apt-cacher-ng's cache.

This is what exactly happened :

On Ubuntu 10.10 & 11.04

  1. apt-cacher-ng installed & configured on my laptop, then I reload and install some packages
  2. After that I configure my friend's laptop with apt-cacher-ng proxy (192.168.1.1:3142), reloading repository was blazingly fast, finished in a second without using my Internet connection (checked on system monitor, total Received just 15kB)

On Ubuntu 11.10 & 12.04

  1. apt-cacher-ng installed and configured on my laptop, then I reload and install some packages
  2. After that I configure my friend's laptop with apt-cacher-ng proxy (192.168.1.1:3142), reloading repository was really slow!, apt-cacher-ng redownload the index file from the Internet.
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3 Answers 3

up vote 2 down vote accepted

The unexpected redownloads you experience are most likely caused by this bug in the archive infrastructure:

https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1001780

Every two hours all packages files are updated to the current date. Thus they count as new, even with unchanged content, and get downloaded again. This also affects the main distribution packages files which usually remain unchanged until a point release.

Please tick "this bug affects me too" on the launchpad page, if possible.

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Most likely the file has been changed in the meantime. If you want to reproduce it, copy the related .head file from the cache next time before running update, and compare it with the new version afterwards.

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In the apt-cacher-ng dashboard (open http://localhost:3142/acng-report.html), there is an option called "Force the download of index files (even having fresh ones)". It is probably turned on.

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