Abstract ZODB's MVCC implementation into a storage adapter.

That's applied to storages other than RelStorage.

See: https://groups.google.com/forum/#!topic/zodb/QJYmvF0eUUM

setup.py

@@ -20,7 +20,7 @@
 interface, rich transaction support, and undo.
 """
 
-version = "4.3.0.dev0"
+version = "5.0.dev0"
 
 import os
 from setuptools import setup, find_packages

src/ZODB/DB.py

@@ -401,12 +401,6 @@ def __init__(self, storage,
           - `xrefs` - Boolian flag indicating whether implicit cross-database
             references are allowed
         """
-        if isinstance(storage, six.string_types):
-            from ZODB import FileStorage
-            storage = ZODB.FileStorage.FileStorage(storage, **storage_args)
-        elif storage is None:
-            from ZODB import MappingStorage
-            storage = ZODB.MappingStorage.MappingStorage(**storage_args)
 
         # Allocate lock.
         x = utils.RLock()
@@ -423,12 +417,24 @@ def __init__(self, storage,
         self._historical_cache_size_bytes = historical_cache_size_bytes
 
         # Setup storage
+        if isinstance(storage, six.string_types):
+            from ZODB import FileStorage
+            storage = ZODB.FileStorage.FileStorage(storage, **storage_args)
+        elif storage is None:
+            from ZODB import MappingStorage
+            storage = ZODB.MappingStorage.MappingStorage(**storage_args)
+        else:
+            assert not storage_args
+
         self.storage = storage
+
+        if IMVCCStorage.providedBy(storage):
+            self._mvcc_storage = storage
+        else:
+            from .mvccadapter import MVCCAdapter
+            self._mvcc_storage = MVCCAdapter(storage)
+
         self.references = ZODB.serialize.referencesf
-        try:
-            storage.registerDB(self)
-        except TypeError:
-            storage.registerDB(self, None) # Backward compat
 
         if (not hasattr(storage, 'tpc_vote')) and not storage.isReadOnly():
             warnings.warn(
@@ -438,12 +444,10 @@ def __init__(self, storage,
                 DeprecationWarning, 2)
             storage.tpc_vote = lambda *args: None
 
-        if IMVCCStorage.providedBy(storage):
-            temp_storage = storage.new_instance()
-        else:
-            temp_storage = storage
+        temp_storage = self._mvcc_storage.new_instance()
         try:
             try:
+                temp_storage.poll_invalidations()
                 temp_storage.load(z64, '')
             except KeyError:
                 # Create the database's root in the storage if it doesn't exist
@@ -462,8 +466,7 @@ def __init__(self, storage,
                 temp_storage.tpc_vote(t)
                 temp_storage.tpc_finish(t)
         finally:
-            if IMVCCStorage.providedBy(temp_storage):
-                temp_storage.release()
+            temp_storage.release()
 
         # Multi-database setup.
         if databases is None:
@@ -634,16 +637,13 @@ def close(self):
 
         @self._connectionMap
         def _(c):
-            if c.opened:
-                c.transaction_manager.abort()
-                # Note that this will modify our pool, but this is safe, because
-                # _connectionMap makes a list of the pool to iterate over
-                c.close()
+            c.transaction_manager.abort()
             c.afterCompletion = c.newTransaction = c.close = noop
             c._release_resources()
 
-        self.storage.close()
+        self._mvcc_storage.close()
         del self.storage
+        del self._mvcc_storage
 
     def getCacheSize(self):
         return self._cache_size
@@ -675,27 +675,6 @@ def getHistoricalPoolSize(self):
     def getHistoricalTimeout(self):
         return self.historical_pool.timeout
 
-    def invalidate(self, tid, oids, connection=None, version=''):
-        """Invalidate references to a given oid.
-
-        This is used to indicate that one of the connections has committed a
-        change to the object.  The connection commiting the change should be
-        passed in to prevent useless (but harmless) messages to the
-        connection.
-        """
-        # Storages, esp. ZEO tests, need the version argument still. :-/
-        assert version==''
-        # Notify connections.
-        def inval(c):
-            if c is not connection:
-                c.invalidate(tid, oids)
-        self._connectionMap(inval)
-
-    def invalidateCache(self):
-        """Invalidate each of the connection caches
-        """
-        self._connectionMap(lambda c: c.invalidateCache())
-
     transform_record_data = untransform_record_data = lambda self, data: data
 
     def objectCount(self):
@@ -1001,9 +980,9 @@ class TransactionalUndo(object):
 
     def __init__(self, db, tids):
         self._db = db
-        self._storage = db.storage
+        self._storage = getattr(
+            db._mvcc_storage, 'undo_instance', db._mvcc_storage.new_instance)()
         self._tids = tids
-        self._oids = set()
 
     def abort(self, transaction):
         pass
@@ -1013,19 +992,13 @@ def tpc_begin(self, transaction):
 
     def commit(self, transaction):
         for tid in self._tids:
-            result = self._storage.undo(tid, transaction)
-            if result:
-                self._oids.update(result[1])
+            self._storage.undo(tid, transaction)
 
     def tpc_vote(self, transaction):
-        for oid, _ in  self._storage.tpc_vote(transaction) or ():
-            self._oids.add(oid)
+        self._storage.tpc_vote(transaction)
 
     def tpc_finish(self, transaction):
-        self._storage.tpc_finish(
-            transaction,
-            lambda tid: self._db.invalidate(tid, self._oids)
-            )
+        self._storage.tpc_finish(transaction)
 
     def tpc_abort(self, transaction):
         self._storage.tpc_abort(transaction)

src/ZODB/historical_connections.txt

@@ -273,8 +273,6 @@ test.
     >>> conn.root()['first']['count'] += 1
     >>> conn.root()['third'] = persistent.mapping.PersistentMapping()
     >>> transaction.commit()
-    >>> len(historical_conn._invalidated)
-    0
     >>> historical_conn.close()
 
 Note that if you try to open an historical connection to a time in the future,