James Henstridge wrote: > 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 wouldn't call any of these a point of contention. They where points of
discussion. Attempting to remove the xid() constructor from the spec is
premature when people where just considering if tuples can be used instead.
I don't think omitting transaction ids from tpc_recover() is acceptable.
Doing so means you can't write a transaction manager that plays nicely in a
more complex environment where components may not be under our direct
control, let alone written in Python and using ths API. My use case here is
a reaper script that detects and handles or reports lost transactions.
Here is an edge case with proposal 1. Here, con happens to be a connection
to a MySQL database. Which Xid represents the prepared transaction?
>>> con.tpc_begin('foo')
>>> con.tpc_prepare()
>>> con.tpc_recover()
[<Xid 'foo', '', 1>, <Xid 'foo', '', 0>, <Xid 'foo', 'None', 1>]
You could try fixing this by returning a heterogeneous list, but I think
this is just making the hole deeper:
>>> con.tpc_begin('foo')
>>> con.tpc_prepare()
>>> con.tpc_recover()
['foo', <Xid 'foo', '', 0>, <Xid 'foo', 'None', 1>]
Proposal 2 seems the better option. I think we need to specify that the
3-tuple cannot contain None values.
I personally feel that an Xid() constructor makes things more readable. It
also means we can have driver specific defaults for the format id rather
than no default.
tpc_begin(Xid('foo', 'bar', 1)) vs. tpc_begin(('foo', 'bar', 1))
tpc_begin(Xid('foo', 'bar')) vs. tpc_begin(('foo', 'bar', 1))
tpc_begin(Xid('foo')) vs. tpc_begin(('foo', '', 1))
--
Stuart Bishop <[EMAIL PROTECTED]>
http://www.stuartbishop.net/
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