[DB-SIG] Two phase commit API

[David Rushby]

--- Stuart Bishop <stuart at stuartbishop.net> wrote:
> Are there any drivers out there that support two phase commit.

KInterbasDB does.

> If so, what syntax do they use?

The Connection class has a prepare method that triggers the first phase
of two-phase commit.  The normal commit method then performs the second
phase.

There's also a ConnectionGroup class that makes it more convenient to
deal with a group of Connections that are all participating in the same
distributed transaction.

Here's an example:
---
import kinterbasdb

# Establish multiple connections the usual way:
con1 = kinterbasdb.connect(dsn='weasel:/temp/test.db', user='sysdba',
password='pass')
con2 = kinterbasdb.connect(dsn='coyote:/temp/test.db', user='sysdba',
password='pass')

# Create a ConnectionGroup to associate multiple connections in such a
# way that they can participate in a distributed transaction.
group = kinterbasdb.ConnectionGroup(connections=(con1,con2))

# Start a distributed transaction involving all of the members of 
# the group (con1 and con2 in this case) with one of the following
# approaches:
#   - Call  group.begin()
#   - Call  con1.begin(); the operation will "bubble upward" and 
#     apply to the group.
#   - Call  con2.begin(); the operation will "bubble upward" and 
#     apply to the group.
#   - Just start executing some SQL statements on either con1 or con2.
#     A transaction will be started implicitly; it will be a 
#     distributed transaction because con1 and con2 are members 
#     of a ConnectionGroup.
group.begin()

# Perform some database changes the usual way (via cursors on con1 and
con2):
...

# Commit or roll back the distributed transaction by calling the 
# commit or rollback method of the ConnectionGroup itself, or the
# commit or rollback method of any member connection (con1 or 
# con2 in this case).
group.commit()

# Unless you want to perform another distributed transaction, 
# disband the group so that member connections can operate 
# independently again.
group.clear()
---

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