[ZODB-Dev] Merge request - transaction savepoint release support

[Jim Fulton]

Thanks! I'll review and presumably merge this as soon as I can.

JIm

On Mon, Jun 7, 2010 at 12:45 PM, Laurence Rowe <l at lrowe.co.uk> wrote:
> Hi Jim,
>
> I've created a new branch for my savepoint release changes following
> the 1.1 release here:
>
>  svn+ssh://svn.zope.org/repos/main/transaction/branches/elro-savepoint-release-1.1
>
> This does seem to be a real requirement, as I've had another request
> to provide this functionality for zope.sqlalchemy - when a large
> number of savepoints are used, the eventual commit can lead to a
> `RuntimeError: maximum recursion depth exceeded` in SQLAlchemy as it
> attempts to unroll its nested substransactions.
>
> Laurence
>
> On 17 January 2010 15:45, Laurence Rowe <l at lrowe.co.uk> wrote:
>> 2010/1/17 Jim Fulton <jim at zope.com>:
>>> On Sat, Jan 16, 2010 at 1:03 PM, Laurence Rowe <l at lrowe.co.uk> wrote:
>>>> I've had a request to add savepoint release support to zope.sqlalchemy
>>>> as some databases seem to limit the number of savepoints in a
>>>> transaction.
>>>>
>>>> I've added this in a branch of transaction here:
>>>> svn+ssh://svn.zope.org/repos/main/transaction/branches/elro-savepoint-release
>>>>
>>>> >From the changelog:
>>>>
>>>> * Add support for savepoint.release(). Some databases only support a limited
>>>>  number of savepoints or subtransactions, this provides an opportunity for a
>>>>  data manager to free those resources.
>>>>
>>>> * Rename InvalidSavepointRollbackError to InvalidSavepointError (BBB provided.)
>>>>
>>>> If there are no objections, I shall merge this to trunk.
>>>
>>> I'll review and merge.
>>
>> Great, thanks!
>>
>>> What does it mean to "release" a savepoint? How is this different from aborting
>>> a save point? I ask particularly in light of:
>>>
>>> On Sat, Jan 16, 2010 at 2:26 PM, Laurence Rowe <l at lrowe.co.uk> wrote:
>>>> 2010/1/16 Laurence Rowe <l at lrowe.co.uk>:
>>>>> I'm still not sure this will allow me to add savepoint release support
>>>>> to zope.sqlalchemy, as SQLAlchemy has a concept of nested transactions
>>>>> rather than savepoints.
>>>>> http://groups.google.com/group/sqlalchemy/browse_thread/thread/7a4632587fd97724
>>>>
>>>> Michael Bayer noted on the sqlalchemy group that on RELEASE SAVEPOINT
>>>> Postgresql destroys all subsequent savepoints. My branch now
>>>> implements this behaviour.
>>
>> For zope.sqlalchemy I commit the sqlalchemy substransaction on
>> savepoint.release(). This translates to a RELEASE SAVEPOINT on
>> postgresql, best described by their docs here:
>>
>> """
>> RELEASE SAVEPOINT destroys a savepoint previously defined in the
>> current transaction.
>>
>> Destroying a savepoint makes it unavailable as a rollback point, but
>> it has no other user visible behavior. It does not undo the effects of
>> commands executed after the savepoint was established. (To do that,
>> see ROLLBACK TO SAVEPOINT.) Destroying a savepoint when it is no
>> longer needed allows the system to reclaim some resources earlier than
>> transaction end.
>>
>> RELEASE SAVEPOINT also destroys all savepoints that were established
>> after the named savepoint was established.
>> """
>> http://developer.postgresql.org/pgdocs/postgres/sql-release-savepoint.html
>>
>> Laurence
>>
>



-- 
Jim Fulton