[Engine-devel] Global transaction in ovirt-engine

[Omer Frenkel]

----- 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
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> Engine-devel at ovirt.org
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> 

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..