[Engine-devel] Global transaction in ovirt-engine

[Michael Kublin]

----- Original Message -----
> From: "Omer Frenkel" <ofrenkel at redhat.com>
> To: "Michael Kublin" <mkublin at redhat.com>
> Cc: "engine-devel" <engine-devel at ovirt.org>
> Sent: Tuesday, February 12, 2013 4:32:44 PM
> Subject: Re: [Engine-devel] Global transaction in ovirt-engine
> 
> 
> 
> ----- Original Message -----
> > From: "Michael Kublin" <mkublin at redhat.com>
> > To: "engine-devel" <engine-devel at ovirt.org>
> > Sent: Tuesday, February 12, 2013 11:38:33 AM
> > Subject: [Engine-devel] Global transaction in ovirt-engine
> > 
> > The issue is a following (I think I had raised it once),
> > by default when any command is invoked in ovirt-engine a
> > transaction
> > is opened.
> > Now, lets take a look on complicated command which is performing a
> > lot of XML-RPC/HTTP calls and just simple update ,
> > such command is a main cause for the following problems:
> > 1. Long transactions, each call increase a time of transaction
> > 2. When transaction is opened a connection which is associated with
> > it also in used, so a number of available DB connections reduced
> > from
> > connection pool.
> > 3. A errors : transaction was cancelled and operation is failed on
> > engine side, but successes at host side.
> > 4. Performance - "try to keep transactions as short as possible".
> > 5. Performance - to many unneeded transactions
> > 6. Bug debugging - it is very difficult to understand why something
> > was committed and something not why transaction was reverted or
> > not,
> >    when we have a lot of nested transactions.
> > 
> > Now, what should be done by my opinion:
> > 1. Change default behaviour - by default not to open a transaction
> > (Today, transaction is opened and if we don't want a command should
> > be marked
> >    by NonTransactiveCommandAttribute) - it is simple
> > 2. The change described at 1 will require to rewrite and redesign
> > some flows - more difficult, but also can be done pretty fast.
> >    By the way this can be or even should be done at any case.
> > 3. All new commands should not be based on global transaction or
> > keep
> > in mind that global transaction can be disabled
> > 
> > Benefits,
> > 1. Better performance
> > 2. Cleaner code
> > 3. Less bugs
> > 4. Increased scale
> > 
> > Regards Michael
> > _______________________________________________
> > Engine-devel mailing list
> > Engine-devel at ovirt.org
> > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > 
> 
> need to remember that transaction also gave us 10-min limit for
> command execution,
> not saying its good or bad, but disabling the transactions will allow
> commands to run forever,
> this 10 min limit actually, saved us few times when commands got
> stuck in all kind of locks etc..
> 
Not exactly, if transaction has expired the JBOSS transaction framework (Arjuna)
will not stop a running thread attached to such thread.
We can configure it in such way that a running thread will be cancelled, but for now
it is not.