[DB-SIG] Two-phase commit API proposal (was Re: Any standard for two phase commit APIs?)
M.-A. Lemburg
mal at egenix.com
Thu Jan 24 15:36:30 CET 2008
On 2008-01-24 02:44, James Henstridge wrote:
> I've had a bit more time to think about this, and have two proposals
> on how to handle transaction IDs. I think they offer equivalent
> functionality, so the choice comes down to what we want the API to
> look like.
>
> Proposal 1:
> * Plain string IDs should work fine as transaction identifiers for
> applications built from scratch with that assumption: they would
> need to identify the global and branch parts in their own way.
>
> * A plain string can be stuffed inside an XA style transaction
> identifier, even if it isn't making use of all the different
> components.
>
> * Therefore, all methods accepting transaction IDs should accept
> strings.
>
> * As some transaction IDs in the database might not match this simple
> form, there are two options for the recover() method:
> 1. return a special object that represents the transaction, which
> will be accepted by commit()/rollback(). How string-like must
> these objects be?
> 2. omit such transaction IDs from the result.
>
> * For databases that support more structured transaction IDs (such as
> those used by XA), the 2PC methods may accept objects other than
> strings.
>
>
> Proposal 2:
>
> * Many databases follow the XA specification, so it makes sense to use
> transaction identifiers structured in the same way.
>
> * For databases that do not use XA-style transaction IDs, it is
> usually possible to serialise such an ID into a form that it can
> work with.
>
> * Therefore, all methods accepting transaction IDs should accept
> 3-sequences of the form (formatID, gtrid, bqual).
>
> * For databases using non-XA transaction IDs, it is possible that some
> transaction IDs might exist that do not match the serialised form.
> The recover() method has two options:
> 1. return a special object representing the ID that will be
> accepted by commit()/rollback(). Such an object should act
> like a 3-sequence.
> 2. omit such transaction IDs from the result.
>
> * For databases not using XA-style transactions, the 2PC methods may
> accept objects other than 3-sequences as transaction IDs.
>
>
> Both of these proposals seem to get rid of the main points of contention:
> * removes the xid() constructor from the spec.
> * allow use of simple objects (strings or tuples) as transaction IDs
> * provides an obvious way to expose database-specific transaction IDs.
I'm coming to agree with Stuart that the conn.xid() might actually
help us with this.
So I'd be in favor of proposal 2 and an .xid() constructor that
returns an object which provides a 3-sequence interface, e.g.
# Wrap the IDs for use by the database module
xid = conn.xid(fid, gid, bid)
# Use the xid
conn.tpc_begin(xid)
conn.tpc_prepare(xid)
...
# Unwrap the IDs:
fid, gid, bid = xid
--
Marc-Andre Lemburg
eGenix.com
Professional Python Services directly from the Source (#1, Jan 24 2008)
>>> Python/Zope Consulting and Support ... http://www.egenix.com/
>>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/
>>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/
________________________________________________________________________
:::: Try mxODBC.Zope.DA for Windows,Linux,Solaris,MacOSX for free ! ::::
eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48
D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg
Registered at Amtsgericht Duesseldorf: HRB 46611
More information about the DB-SIG
mailing list