[ZODB-Dev] snapshot isolation how-to

[Shane Hathaway]

Jeremy Hylton wrote:
> On Tue, 2003-04-15 at 16:43, Shane Hathaway wrote:
> 
>>It's an experimental feature.  It binds transactions to the connection 
>>rather than the thread, allowing you to run multiple transactions in a 
>>single thread.  Use of setLocalTransaction() is not generally compatible 
>>with Zope.
> 
> 
> I was wondering, though, how a local transaction becomes unset.  I think
> we need to flesh out the interface a bit more.  It looks like a
> connection that calls setLocalTransaction() can only participate in one
> transaction.  I don't see any code that clears _transaction when it
> commits.

The connection reuses the same Transaction object for further transactions.

> I'm also not clear on what happens when a Connection calls
> getTransaction() before setLocalTransaction().  It looks like the
> Connection will get hooked up to two transactions.

Yes, that's why the application should call setLocalTransaction() as 
soon as it has the connection object.  A connection can operate in 
either mode but not both.

Here's another possible way to do this.  Maybe the DB.open() method 
should accept an optional "local_transactions" boolean argument.  That 
way, there's no chance to switch modes too late, and the connection will 
never wind up in multiple transactions (hopefully.)

Shane