[DB-SIG] Two-phase commit API proposal (was Re: Any standard for two phase commit APIs?)

[M.-A. Lemburg]

On 2008-01-21 13:10, James Henstridge wrote:
> On 21/01/2008, M.-A. Lemburg <mal at egenix.com> wrote:
>> Thanks for the explanations. I was actually thinking of the
>> connection between the TM and the RM (the database backend).
>> The typical behavior of a TM is to cancel the ongoing
>> two-phase commit transaction if an RM becomes unavailable.
> 
> Stuart's use case is if the RM dies during the second phase of the
> commit.  It is an edge case, but then 2PC is all about edge cases :)
> 
> If it happens before that point, then rolling back is appropriate.
> 
> 
>> However, I can see your point. If the data stays on the
>> database server and can be addressed via the XID, then a
>> dropped connection wouldn't hurt all that much.
>> Then again: how do you tell the database to forget about
>> the data stored for an XID ?
> 
> You ask for the transaction to be rolled back (e.g. "ROLLBACK PREPARED
> xid" in PostgreSQL, and "XA ROLLBACK xid" for MySQL).

Sorry, I wasn't clear enough:

If a connection fails and the transaction XID persists, how do you:

 * identify which XIDs are still pending (xa_recover)

 * tell the RM to drop all resources associacted with an XID
   (xa_forget)

once the TM has reconnected. These APIs appear to be needed
in order for the TM to be able to cleanup the RM after e.g.
a lost connection.

OTOH, perhaps just doing a rollback with the known XID and
ignoring any errors would do the same without the need for
extra APIs.

-- 
Marc-Andre Lemburg
eGenix.com

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