My favorite pet bug (2004): Yum mishandles Ctrl-C

[Patrick W. Barnes]

On Thursday 31 August 2006 14:07, Richard Hally <rhally at mindspring.com> wrote:
> Matthew Miller wrote:
> > On Thu, Aug 31, 2006 at 01:32:05PM -0400, Bill Nottingham wrote:
> >>> transaction != atomic transaction.
> >>
> >> Please allow 4 to 6 weeks for package delivery.
> >
> > And, bizarrely, be prepared to end up with duplicate packages if there's
> > a shipping problem.
>
> and if you are not there to take delivery we will just dump it on your
> driveway and you will have to spread it on your garden yourself. (wink)
>
> But seriously, without being too pedantic about it, "atomic transaction"
> could be considered redundant. In database terms, a "transaction" can be
> applied or rolled back and the integrity of the database is preserved in
> either case. The smaller the "transaction" size the easier it is to
> preserve the database integrity.
>
> Aw, never mind. We can just use that script on the yum hints page in the
> wiki.
>

Going further on the database terms, most of the work you do on a transaction 
is *preparing* the transaction.  Once the transaction is *ready*, you have a 
final opportunity to cancel the transaction before you *commit* the 
transaction.  The commit stage is where the real work of the transaction is 
done, and it is the one stage that you don't want to interrupt.  When you 
decide to cancel a transaction after the commit stage has begun, you must 
wait until it is done and then prepare a new transaction to roll the previous 
one back, or there's no telling what sort of condition the database will be 
left in.  In a typical RDBMS, you can usually prepare and commit the 
reversing transaction very easily, but that's not always the case.

In yum, the stages of downloading the headers, calculating the dependencies, 
and retrieving the packages are all part of preparing the transaction.  Once 
the packages are downloaded, the transaction is ready and yum begins to 
commit the transaction.  Just like in a database, you do not want to kill yum 
while the transaction is being committed.  You can cancel it beforehand, you 
can roll it back afterwards, but you shouldn't be interrupting it.

-- 
Patrick "The N-Man" Barnes
nman64 at n-man.com

http://www.n-man.com/

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