Commit 9e4121bf authored by Tim Peters's avatar Tim Peters

Checkpointing progress made with Jim so far today.

New interface IResourceManager intends to combine the
best aspects of IDataManager and IDataManagerOriginal,
and will become "the" interface.
New interface ISavePoint captures (along with models in
collaborations.txt) what should be a clean design for a
savepoint/rollback facility that actually works.
parent ff7ff6c1
...@@ -18,6 +18,103 @@ $Id$ ...@@ -18,6 +18,103 @@ $Id$
import zope.interface import zope.interface
class IResourceManager(zope.interface.Interface):
"""Objects that manage resources transactionally.
These objects may manage data for other objects, or they may manage
non-object storages, such as relational databases.
IDataManagerOriginal is the interface currently provided by ZODB
database connections, but the intent is to move to the newer
IDataManager.
"""
# Two-phase commit protocol. These methods are called by the
# ITransaction object associated with the transaction being
# committed.
def tpc_begin(transaction):
"""Begin two-phase commit, to save data changes.
An implementation should do as much work as possible without
making changes permanent. Changes should be made permanent
when tpc_finish is called (or aborted if tpc_abort is called).
The work can be divided between tpc_begin() and tpc_vote(), and
the intent is that tpc_vote() be as fast as possible (to minimize
the period of uncertainty).
transaction is the ITransaction instance associated with the
transaction being committed.
"""
def tpc_vote(transaction):
"""Verify that a resource manager can commit the transaction.
This is the last chance for a resource manager to vote 'no'. A
resource manager votes 'no' by raising an exception.
transaction is the ITransaction instance associated with the
transaction being committed.
"""
def tpc_finish(transaction):
"""Indicate confirmation that the transaction is done.
transaction is the ITransaction instance associated with the
transaction being committed.
This should never fail. If this raises an exception, the
database is not expected to maintain consistency; it's a
serious error.
"""
def tpc_abort(transaction):
"""Abort a transaction.
transaction is the ITransaction instance associated with the
transaction being committed.
All changes made by the current transaction are aborted. Note
that this includes all changes stored in any savepoints that may
be associated with the current transaction.
tpc_abort() can be called at any time, either in or out of the
two-phase commit.
This should never fail.
"""
# The savepoint/rollback API.
def savepoint(transaction):
"""Save partial transaction changes.
There are two purposes:
1) To allow discarding partial changes without discarding all
dhanges.
2) To checkpoint changes to disk that would otherwise live in
memory for the duration of the transaction.
Returns an object implementing ISavePoint2 that can be used
to discard changes made since the savepoint was captured.
An implementation that doesn't support savepoints should implement
this method by returning a savepoint object that raises an
exception when its rollback method is called. The savepoint method
shouldn't raise an error. This way, transactions that create
savepoints can proceed as long as an attempt is never made to roll
back a savepoint.
"""
def discard(transaction):
"""Discard changes within the transaction since the last savepoint.
That means changes made since the last savepoint if one exists, or
since the start of the transaction.
"""
class IDataManagerOriginal(zope.interface.Interface): class IDataManagerOriginal(zope.interface.Interface):
"""Objects that manage transactional storage. """Objects that manage transactional storage.
...@@ -297,6 +394,35 @@ class ITransaction(zope.interface.Interface): ...@@ -297,6 +394,35 @@ class ITransaction(zope.interface.Interface):
# XXX is this this allowed to cause an exception here, during # XXX is this this allowed to cause an exception here, during
# the two-phase commit, or can it toss data silently? # the two-phase commit, or can it toss data silently?
class ISavePoint(zope.interface.Interface):
"""ISavePoint objects represent partial transaction changes.
Sequences of savepoint objects are associated with transactions,
and with IResourceManagers.
"""
def rollback():
"""Discard changes made after this savepoint.
This includes discarding (call the discard method on) all
subsequent savepoints.
"""
def discard():
"""Discard changes saved by this savepoint.
That means changes made since the immediately preceding
savepoint if one exists, or since the start of the transaction,
until this savepoint.
Once a savepoint has been discarded, it's an error to attempt
to rollback or discard it again.
"""
next_savepoint = zope.interface.Attribute(
"""The next savepoint (later in time), or None if self is the
most recent savepoint.""")
class IRollback(zope.interface.Interface): class IRollback(zope.interface.Interface):
def rollback(): def rollback():
......
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