Simplified error handling during vote

ZEO's vote error handling was extremely and weirdly complicated.
There's a hysterical explanation: Originally, the ZEO protocol was
synchronous and mirrored the storage API. That was too slow, so store
was made asynchronous.  But then there was no way to return new
serials, so we added a serialnos client API that the server called
during TPC. This was used both to serials and errors.  Later, tpc_vote
was added, which is a synchronous method. That would have been an
execllent opportunity to fix this, but noooooooooo.

I'd like the server vote logic to get simpler, and we also want to get rid
of serialnos, as it makes it hard to commit multiple transactions at
once on the client.  We can't get rid of serialnos now, because the
client needs to work with old servers.

Of course, nothing is easy. There was a special edge case where if the
client saw an unhandled conflict error, it would invalidate it's cache
for that object, allowing it to eventually recover when caches had
missed invalidations. This required a change to ClientStorage, which
meant that the server wouldn't work with older ZEO versions, which
meant that the server could only support protocol Z5, which in tern
affected protocol-negotiation tests....

src/ZEO/StorageServer.py

@@ -84,7 +84,7 @@ class ZEOStorage:
     blob_tempfile = None
     log_label = 'unconnected'
     locked = False             # Don't have storage lock
-    verifying = store_failed = 0
+    verifying = 0
 
     def __init__(self, server, read_only=0):
         self.server = server
@@ -338,7 +338,6 @@ class ZEOStorage:
         self.blob_log = []
         self.tid = tid
         self.status = status
-        self.store_failed = 0
         self.stats.active_txns += 1
 
         # Assign the transaction attribute last. This is so we don't
@@ -426,29 +425,30 @@ class ZEOStorage:
                     self.storage.tpc_begin(self.transaction)
 
                 for op, args in self.txnlog:
-                    if not getattr(self, op)(*args):
-                        break
+                    getattr(self, op)(*args)
 
 
                 # Blob support
-                while self.blob_log and not self.store_failed:
+                while self.blob_log:
                     oid, oldserial, data, blobfilename = self.blob_log.pop()
                     self._store(oid, oldserial, data, blobfilename)
 
-                if not self.store_failed:
-                    # Only call tpc_vote of no store call failed,
-                    # otherwise the serialnos() call will deliver an
-                    # exception that will be handled by the client in
-                    # its tpc_vote() method.
                 serials = self.storage.tpc_vote(self.transaction)
                 if serials:
                     self.serials.extend(serials)
 
                 self.connection.async('serialnos', self.serials)
 
-            except Exception:
+            except Exception as err:
                 self.storage.tpc_abort(self.transaction)
                 self._clear_transaction()
+
+                if isinstance(err, ConflictError):
+                    self.stats.conflicts += 1
+                    self.log("conflict error %s" % err, BLATHER)
+                if not isinstance(err, TransactionError):
+                    logger.exception("While voting")
+
                 if delay is not None:
                     delay.error(sys.exc_info())
                 else:
@@ -549,60 +549,21 @@ class ZEOStorage:
         self._check_tid(tid, exc=StorageTransactionError)
         self.txnlog.undo(trans_id)
 
-    def _op_error(self, oid, err, op):
-        self.store_failed = 1
-        if isinstance(err, ConflictError):
-            self.stats.conflicts += 1
-            self.log("conflict error oid=%s msg=%s" %
-                     (oid_repr(oid), str(err)), BLATHER)
-        if not isinstance(err, TransactionError):
-            # Unexpected errors are logged and passed to the client
-            self.log("%s error: %s, %s" % ((op,)+ sys.exc_info()[:2]),
-                     logging.ERROR, exc_info=True)
-        err = self._marshal_error(err)
-        # The exception is reported back as newserial for this oid
-        self.serials.append((oid, err))
-
     def _delete(self, oid, serial):
-        err = None
-        try:
         self.storage.deleteObject(oid, serial, self.transaction)
-        except (SystemExit, KeyboardInterrupt):
-            raise
-        except Exception as e:
-            err = e
-            self._op_error(oid, err, 'delete')
-
-        return err is None
 
     def _checkread(self, oid, serial):
-        err = None
-        try:
         self.storage.checkCurrentSerialInTransaction(
             oid, serial, self.transaction)
-        except (SystemExit, KeyboardInterrupt):
-            raise
-        except Exception as e:
-            err = e
-            self._op_error(oid, err, 'checkCurrentSerialInTransaction')
-
-        return err is None
 
     def _store(self, oid, serial, data, blobfile=None):
-        err = None
-        try:
         if blobfile is None:
             newserial = self.storage.store(
                 oid, serial, data, '', self.transaction)
         else:
             newserial = self.storage.storeBlob(
                 oid, serial, data, blobfile, '', self.transaction)
-        except (SystemExit, KeyboardInterrupt):
-            raise
-        except Exception as error:
-            self._op_error(oid, error, 'store')
-            err = error
-        else:
+
         if serial != b"\0\0\0\0\0\0\0\0":
             self.invalidated.append(oid)
 
@@ -618,52 +579,15 @@ class ZEOStorage:
 
             self.serials.append((oid, s))
 
-        return err is None
-
     def _restore(self, oid, serial, data, prev_txn):
-        err = None
-        try:
         self.storage.restore(oid, serial, data, '', prev_txn,
                              self.transaction)
-        except (SystemExit, KeyboardInterrupt):
-            raise
-        except Exception as err:
-            self._op_error(oid, err, 'restore')
-
-        return err is None
 
     def _undo(self, trans_id):
-        err = None
-        try:
         tid, oids = self.storage.undo(trans_id, self.transaction)
-        except (SystemExit, KeyboardInterrupt):
-            raise
-        except Exception as e:
-            err = e
-            self._op_error(z64, err, 'undo')
-        else:
         self.invalidated.extend(oids)
         self.serials.extend((oid, ResolvedSerial) for oid in oids)
 
-        return err is None
-
-    def _marshal_error(self, error):
-        # Try to pickle the exception.  If it can't be pickled,
-        # the RPC response would fail, so use something that can be pickled.
-        if PY3:
-            pickler = Pickler(BytesIO(), 3)
-        else:
-            # The pure-python version requires at least one argument (PyPy)
-            pickler = Pickler(0)
-        pickler.fast = 1
-        try:
-            pickler.dump(error)
-        except:
-            msg = "Couldn't pickle storage exception: %s" % repr(error)
-            self.log(msg, logging.ERROR)
-            error = StorageServerError(msg)
-        return error
-
     # IStorageIteration support
 
     def iterator_start(self, start, stop):

src/ZEO/asyncio/server.py

@@ -17,7 +17,7 @@ class ServerProtocol(base.Protocol):
     """asyncio low-level ZEO server interface
     """
 
-    protocols = b'Z4', b'Z5'
+    protocols = (b'Z5', )
 
     name = 'server protocol'
     methods = set(('register', ))
@@ -161,7 +161,7 @@ class Delay:
 
     def error(self, exc_info):
         self.sent = 'error'
-        log("Error raised in delayed method", logging.ERROR, exc_info=exc_info)
+        logger.error("Error raised in delayed method", exc_info=exc_info)
         self.protocol.send_error(self.msgid, exc_info[1])
 
     def __repr__(self):
@@ -198,5 +198,4 @@ class MTDelay(Delay):
 
     def error(self, exc_info):
         self.ready.wait()
-        log("Error raised in delayed method", logging.ERROR, exc_info=exc_info)
         self.protocol.call_soon_threadsafe(Delay.error, self, exc_info)

src/ZEO/asyncio/tests.py

@@ -750,7 +750,7 @@ class ServerTests(Base, setupstack.TestCase):
         self.target = protocol.zeo_storage
         if finish:
             self.assertEqual(self.pop(parse=False), best_protocol_version)
-            protocol.data_received(sized(b'Z4'))
+            protocol.data_received(sized(b'Z5'))
         return protocol
 
     message_id = 0
@@ -788,9 +788,9 @@ class ServerTests(Base, setupstack.TestCase):
         self.assertEqual(self.pop(parse=False), best_protocol_version)
 
         # The client sends it's protocol:
-        protocol.data_received(sized(b'Z4'))
+        protocol.data_received(sized(b'Z5'))
 
-        self.assertEqual(protocol.protocol_version, b'Z4')
+        self.assertEqual(protocol.protocol_version, b'Z5')
 
         protocol.zeo_storage.notify_connected.assert_called_once_with(protocol)
 

src/ZEO/tests/forker.py

@@ -94,6 +94,10 @@ def runner(config, qin, qout, timeout=None,
         import ZEO.asyncio.server
         old_protocol = ZEO.asyncio.server.best_protocol_version
         ZEO.asyncio.server.best_protocol_version = protocol
+        old_protocols = ZEO.asyncio.server.ServerProtocol.protocols
+        ZEO.asyncio.server.ServerProtocol.protocols = tuple(sorted(
+            set(old_protocols) | set([protocol])
+            ))
 
     try:
         import ZEO.runzeo, threading
@@ -144,8 +148,8 @@ def runner(config, qin, qout, timeout=None,
 
     finally:
         if old_protocol:
-            ZEO.asyncio.server.best_protocol_version = protocol
-
+            ZEO.asyncio.server.best_protocol_version = old_protocol
+            ZEO.asyncio.server.ServerProtocol.protocols = old_protocols
 
 def stop_runner(thread, config, qin, qout, stop_timeout=9, pid=None):
     qin.put('stop')

src/ZEO/tests/protocols.test

@@ -5,7 +5,7 @@ A full test of all protocols isn't practical.  But we'll do a limited
 test that at least the current and previous protocols are supported in
 both directions.
 
-Let's start a Z309 server
+Let's start a Z4 server
 
     >>> storage_conf = '''
     ... <blobstorage>
@@ -94,82 +94,85 @@ A current client should be able to connect to a old server:
     >>> zope.testing.setupstack.rmtree('blobs')
     >>> zope.testing.setupstack.rmtree('server-blobs')
 
-And the other way around:
+#############################################################################
+# Note that the ZEO 5.0 server only supports clients that use the Z5 protocol
 
-    >>> addr, _ = start_server(storage_conf, dict(invalidation_queue_size=5))
+# And the other way around:
 
-Note that we'll have to pull some hijinks:
+#     >>> addr, _ = start_server(storage_conf, dict(invalidation_queue_size=5))
 
-    >>> import ZEO.asyncio.client
-    >>> old_protocols = ZEO.asyncio.client.Protocol.protocols
-    >>> ZEO.asyncio.client.Protocol.protocols = [b'Z4']
+# Note that we'll have to pull some hijinks:
 
-    >>> db = ZEO.DB(addr, client='client', blob_dir='blobs')
-    >>> db.storage.protocol_version
-    b'Z4'
-    >>> wait_connected(db.storage)
-    >>> conn = db.open()
-    >>> conn.root().x = 0
-    >>> transaction.commit()
-    >>> len(db.history(conn.root()._p_oid, 99))
-    2
+#     >>> import ZEO.asyncio.client
+#     >>> old_protocols = ZEO.asyncio.client.Protocol.protocols
+#     >>> ZEO.asyncio.client.Protocol.protocols = [b'Z4']
 
-    >>> conn.root()['blob1'] = ZODB.blob.Blob()
-    >>> with conn.root()['blob1'].open('w') as f:
-    ...    r = f.write(b'blob data 1')
-    >>> transaction.commit()
+#     >>> db = ZEO.DB(addr, client='client', blob_dir='blobs')
+#     >>> db.storage.protocol_version
+#     b'Z4'
+#     >>> wait_connected(db.storage)
+#     >>> conn = db.open()
+#     >>> conn.root().x = 0
+#     >>> transaction.commit()
+#     >>> len(db.history(conn.root()._p_oid, 99))
+#     2
 
-    >>> db2 = ZEO.DB(addr, blob_dir='server-blobs', shared_blob_dir=True)
-    >>> wait_connected(db2.storage)
-    >>> conn2 = db2.open()
-    >>> for i in range(5):
-    ...     conn2.root().x += 1
-    ...     transaction.commit()
-    >>> conn2.root()['blob2'] = ZODB.blob.Blob()
-    >>> with conn2.root()['blob2'].open('w') as f:
-    ...    r = f.write(b'blob data 2')
-    >>> transaction.commit()
+#     >>> conn.root()['blob1'] = ZODB.blob.Blob()
+#     >>> with conn.root()['blob1'].open('w') as f:
+#     ...    r = f.write(b'blob data 1')
+#     >>> transaction.commit()
 
+#     >>> db2 = ZEO.DB(addr, blob_dir='server-blobs', shared_blob_dir=True)
+#     >>> wait_connected(db2.storage)
+#     >>> conn2 = db2.open()
+#     >>> for i in range(5):
+#     ...     conn2.root().x += 1
+#     ...     transaction.commit()
+#     >>> conn2.root()['blob2'] = ZODB.blob.Blob()
+#     >>> with conn2.root()['blob2'].open('w') as f:
+#     ...    r = f.write(b'blob data 2')
+#     >>> transaction.commit()
 
-    >>> @wait_until()
-    ... def x_to_be_5():
-    ...     conn.sync()
-    ...     return conn.root().x == 5
 
-    >>> db.close()
+#     >>> @wait_until()
+#     ... def x_to_be_5():
+#     ...     conn.sync()
+#     ...     return conn.root().x == 5
 
-    >>> for i in range(2):
-    ...     conn2.root().x += 1
-    ...     transaction.commit()
+#     >>> db.close()
 
-    >>> db = ZEO.DB(addr, client='client', blob_dir='blobs')
-    >>> wait_connected(db.storage)
-    >>> conn = db.open()
-    >>> conn.root().x
-    7
+#     >>> for i in range(2):
+#     ...     conn2.root().x += 1
+#     ...     transaction.commit()
 
-    >>> db.close()
+#     >>> db = ZEO.DB(addr, client='client', blob_dir='blobs')
+#     >>> wait_connected(db.storage)
+#     >>> conn = db.open()
+#     >>> conn.root().x
+#     7
 
-    >>> for i in range(10):
-    ...     conn2.root().x += 1
-    ...     transaction.commit()
+#     >>> db.close()
 
-    >>> db = ZEO.DB(addr, client='client', blob_dir='blobs')
-    >>> wait_connected(db.storage)
-    >>> conn = db.open()
-    >>> conn.root().x
-    17
+#     >>> for i in range(10):
+#     ...     conn2.root().x += 1
+#     ...     transaction.commit()
 
-    >>> with conn.root()['blob1'].open() as f:
-    ...    f.read()
-    b'blob data 1'
-    >>> with conn.root()['blob2'].open() as f:
-    ...    f.read()
-    b'blob data 2'
+#     >>> db = ZEO.DB(addr, client='client', blob_dir='blobs')
+#     >>> wait_connected(db.storage)
+#     >>> conn = db.open()
+#     >>> conn.root().x
+#     17
 
-    >>> db2.close()
-    >>> db.close()
+#     >>> with conn.root()['blob1'].open() as f:
+#     ...    f.read()
+#     b'blob data 1'
+#     >>> with conn.root()['blob2'].open() as f:
+#     ...    f.read()
+#     b'blob data 2'
+
+#     >>> db2.close()
+#     >>> db.close()
 
-Undo the hijinks:
+# Undo the hijinks:
 
-    >>> ZEO.asyncio.client.Protocol.protocols = old_protocols
+#     >>> ZEO.asyncio.client.Protocol.protocols = old_protocols

src/ZEO/tests/testZEO2.py

@@ -78,6 +78,8 @@ will conflict. It will be blocked at the vote call.
     >>> class Sender:
     ...     def send_reply(self, id, reply):
     ...         print('reply', id, reply)
+    ...     def send_error(self, id, err):
+    ...         print('error', id, err)
     >>> delay.set_sender(1, Sender())
 
     >>> logger = logging.getLogger('ZEO')
@@ -87,13 +89,20 @@ will conflict. It will be blocked at the vote call.
 
 Now, when we abort the transaction for the first client. The second
 client will be restarted.  It will get a conflict error, that is
-handled correctly:
+raised to the client:
 
     >>> zs1.tpc_abort('0') # doctest: +ELLIPSIS
-    reply 1 None
+    Error raised in delayed method
+    Traceback (most recent call last):
+    ...
+    ZODB.POSException.ConflictError: ...
+    error 1 database conflict error ...
+
+The transaction is aborted by the server:
 
-    >>> fs.tpc_transaction() is not None
+    >>> fs.tpc_transaction() is None
     True
+
     >>> zs2.connected
     True
 
@@ -116,7 +125,7 @@ And an initial client.
 
     >>> zs1 = ZEO.tests.servertesting.client(server, 1)
     >>> zs1.tpc_begin('0', '', '', {})
-    >>> zs1.storea(ZODB.utils.p64(99), ZODB.utils.z64, 'x', '0')
+    >>> zs1.storea(ZODB.utils.p64(99), ZODB.utils.z64, b'x', '0')
 
 Intentionally break zs1:
 
@@ -135,7 +144,7 @@ We can start another client and get the storage lock.
 
     >>> zs1 = ZEO.tests.servertesting.client(server, 1)
     >>> zs1.tpc_begin('1', '', '', {})
-    >>> zs1.storea(ZODB.utils.p64(99), ZODB.utils.z64, 'x', '1')
+    >>> zs1.storea(ZODB.utils.p64(99), ZODB.utils.z64, b'x', '1')
     >>> _ = zs1.vote('1') # doctest: +ELLIPSIS
 
     >>> zs1.tpc_finish('1').set_sender(0, zs1.connection)