Re: 2PC transaction id

On 30-Jun-05, at 8:00 PM, Oliver Jowett wrote:

> Dave Cramer wrote:
>
>> I'm thinking of the situation where one transaction occurs on  
>> more  than
>> one backend, and there is
>> more than one transaction manager.
>>
>
> XA XIDs are *global* IDs, i.e. they are unique even with more than one
> TM involved. It's the responsibility of the TM to generate a
> globally-unique XID.
>
> If you have two different databases involved in the same global
> transaction, then yes, the two backends could be told to use the same
> global XID. That's normal. (they don't *have* to be given the same XID
> as they could be participating in two independent branches of the same
> global transaction, and in that case the global XIDs will have  
> different
> branch qualifiers)
I understand this
>
> It's even possible for one resource to do two different independent
> (local) transactions that are part of the same global transaction  
> -- in
> that case, the local transactions will be given different XIDs though.
>
> But all of this allocation / management of XIDs is done by the TM, the
> individual resources don't need to do anything beyond associating
> particular transactions with client-supplied XIDs, which we already do
> AFAIK.
I was actually thinking more of the people without the advantage of  
an application server
Also for the case where some lowlevel replicator wanted to use 2PC.  
Probably a moot point
as anyone capable of writing one is also capable of getting a unique XID
>
> -O
>
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