More 'About Storm'

[Tres Seaver]

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Gustavo Niemeyer wrote:
>> In integrating the two (storm and zope3/zodb) for the project I'm
>> working on my current plan is to create an IDataManager for storm
>> which will do-the-right-thing(tm) ie: rollback/commit based on the
>> success/failure/readiness of other connections, not sure if this helps
> 
> Zope3's (ZODB's, actually) transaction system indeed offers the needed
> hooks to put the two-phase commit in place, but it doesn't mean that
> it will actually work with anything that hooks into it.  If you have
> two connections and you commit the first one without a two-phase
> commit strategy, you can't roll it back once your second connection
> fails to commit due to some conflict, for instance.

Note that TPC is *alsays* present in ZODB-driven transactions, even
where only a single connection is uesd, and that virtually every Zope
installation running in the world has at least two stores availalbe (the
"main" one and the "temporary" one);  updates which touch both have been
exercising the TPC machnery prety thoroughly.

TPC is also the mechanism used to drive features like transactional mail
delivery[1] in Zope:  the mailer registers as a "mock" connection, which
defers sending mail until the 'tpc_finish' phase.

It is useful to note that the "storages" do not *manage* the TPC
process:  rather, they dance to the tune called by the transaction
object[2] itself.


[1] http://www.dataflake.org/software/maildrophost/

[2] http://svn.zope.org/ZODB/trunk/doc/zodb.pdf, especially
    chapter 4.

Tres.
- --
===================================================================
Tres Seaver          +1 540-429-0999          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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