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Bug#636292: MD5Sum mismatch is due to multiple DNS queries!

X-Debbugs-Cc: spaillard@debian.org, debian-mirrors@lists.debian.org, hmh@debian.org
Package: apt

I think I have a very good idea of what is causing all those MD5Sum
mismatch errors during apt-get update.
( http://article.gmane.org/gmane.linux.debian.user.mirrors/1368 )

You see during a single apt-get update, there will be TWO (2) queries
made to the DNS server for each ONE (1) line in a sources.list file.

I believe one query gets the thing. The other gets the checksum of the

Now you can guess what will happen when that one line is a round robin
site name.

Yup, if the _two different machines_ now being called are slightly out of
sync, naturally the checksums will not match!

The cure is to fix apt so that it only makes one query!

Making a second query not only does not even out the total load on the
servers any more, it also means there are several windows of time each
day when you are comparing apples from machine 1 to oranges from machine
2! Keep it all on one machine and you will be safe.

You can test it yourself. Turn on verbose debugging in your DNS server,
and do apt-get update, and check the log. Voila, two queries for each one line
in sources.list!

Now try a
$ ping example.com

Check your DNS logs. Only one DNS query is made, despite many repeated
connections. Ping has got it right. Apt has got it wrong.

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