[DB-SIG] Two-phase commit API proposal (was Re: Any standard for two phase commit APIs?)
mal at egenix.com
Tue Jan 22 20:31:14 CET 2008
On 2008-01-22 19:48, Dieter Maurer wrote:
> James Henstridge wrote at 2008-1-22 20:33 +0900:
>> I do see a use for the branch qualifier though. In a distributed
>> transaction, each resource should have a different transaction ID
> Why is it not equally good to use a common transaction id for
> all resource managers?
>> share a common global transaction ID but separate branch qualifiers.
>> As transaction IDs are global within database clusters for some
>> backends (PostgreSQL, MySQL and probably others), the branch qualifier
>> is necessary if two databases from the cluster are used in the global
> They refer to the same transaction -- even when several databases
> in a cluster are affected.
> The transaction as a whole will want to get prepared, committed, rolledback...
Sections 2.2.5 and 2.2.6 explain why you need a global transaction
id and a branch id as well:
Branch ids are used for e.g. multiple connections of the same RM
engaging in a global transaction. Each of those connections gets
its own branch id.
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