[DB-SIG] autocommit support in pep-249

Joshua D. Drake jd at commandprompt.com
Tue Sep 13 20:39:18 CEST 2011

On 09/13/2011 10:53 AM, Chris Clark wrote:

>> Just to throw some PostgreSQL two cents in here. It should not be
>> legal to change transaction state once a transaction has begun. The
>> "driver" should throw an error if that is tried. It shouldn't even
>> reach the database. Consider:
>> conn.begin()
>> insert
>> insert
>> At this point we have an open transaction with two inserts pending. We
>> are then going to:
>> conn.autocommit()?
>> Uh, no. The driver should throw an error and the database should
>> remain waiting for next statement whether it be commit or whatever.
> Thanks for the feedback Joshua, could you go in to more detail to
> explain your reasoning please? I think the more justifications we have
> the easier it is to make a decision.
> You made an interesting comment on the autocommit request, "It shouldn't
> even reach the database". I think you are saying the "set auto commit
> on" request should not be sent to the DBMS and be handled by the driver
> when there are open transactions. If I modify your example slightly:
> conn.begin()
> curs.execute('issue server non transaction based directive ') # i.e. not
> dml, not ddl
> curs.execute('issue session directive ') # for example change session
> language of error messages, Oracle NLS settings
> conn.autocommit()

> What should be the behavior be in this instance? No exception being
> raised makes the most sense to me as we are not in a transaction, I'm
> unclear how the driver could make this decision unless it parses and
> understands each curs.execute call.

Oh now that is interesting. Hmmm... perhaps conn.autocommit() is 
actually a synonym for conn.begin() except that it sets the autocommit 
property? So we would have two semantics:

conn.begin() -- Starts a transaction, will not commit unless explicit 
conn.commit() is called.

conn.autocommit() -- Works in autocommit mode, calling conn.commit() is 
redundant, each statement is executed as it is delivered to the database.



Joshua D. Drake

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