Proposal: stop holding composes for preupgrade bugs at Alpha and Beta phases

[John Reiser]

On 04/09/2012 10:05 PM, Dan Mashal top-posted:
> 1) Yum should be intelligent enough to recognize this
> 
> 2) yum-plugin-fastestmirror solves this problem.
> 
> 3) I think we all upgraded from 14.4k modems a few years ago.

Replying in "top post" style may work for a management discussion,
but for a technical discussion it is better for the replies
to follow the quoted relevant sections [trimmed as appropriate].
Then it is easier to associate the specific points, and a top-to-bottom
reading corresponds to chronological order for each point,
which makes the discussion easier to follow.


>>     1. ...    Thus single user mode should
>>         be considered a requirement for distro version upgrade via yum+network,

> 1) Yum should be intelligent enough to recognize this

Until yum is enhanced, preupgrade provides a valuable service:
helping to minimize downtime and avoid silly mistakes.


>>      2. yum is stupidly slow about collecting the upgrade .rpms.
>>         First there is downloading itself: yum downloading [of any kind]
>>         is single threaded.  ...
>>         Second, yum does not download the remaining .rpm (whose .drpm
>>         are not available) while it is reconstituting the other .rpm ...

> 2) yum-plugin-fastestmirror solves this problem.

Are you sure?  The documentation http://wiki.centos.org/PackageManagement/Yum/FastestMirror
does not mention multi-threaded downloading.  It claims only to rate the
available mirrors (and does not specify whether by latency or [near-]peak throughput),
then just give an ordered list to yum.  Single-threaded downloading from the "fastest"
mirror often takes longer to finish the whole job [distro upgrade often involves
hundreds of files] than double-threaded downloading from a mirror with less
single-threaded throughput, because of latency in setup/teardown [thus loss of
average data throughput] for each file.

Also, choice of mirror has no influence on yum's strategy of not downloading
while finishing with the .drpm after the first batch of downloads.


>>      3. If distro version upgrade via yum+network fails (power failure,
>>         network failure, configuration failure, operator error, ...),
>>         then you have a big mess.

> 3) I think we all upgraded from 14.4k modems a few years ago.

Get serious.  Downloading for distro version upgrade can take half an hour
even on a 10Mbit/s to 20Mbit/s cable modem.  That's plenty of time for disaster.
Reliability and Usability (including short and easy cleanup after disaster,
interruptions, or mistakes) are important considerations for users.

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