storage: backend optimizations

Transaction manager uses a new getLastObjectTID method instead of
getObjectHistory, because the latter fetches the data and this is
a waste of time here.

Similarly, minimize SQL work in getObject if the object can't be found.

neo/storage/database/manager.py

@@ -207,6 +207,12 @@ class DatabaseManager(object):
         searched from unfinished transactions as well."""
         raise NotImplementedError
 
+    @fallback
+    def getLastObjectTID(self, oid):
+        """Return the latest tid of given oid or None if it does not exist"""
+        r = self.getObject(oid)
+        return r and r[0]
+
     def _getObject(self, oid, tid=None, before_tid=None):
         """
         oid (int)
@@ -241,27 +247,17 @@ class DatabaseManager(object):
                 - data_serial (packed, None)
         """
         u64 = util.u64
-        p64 = util.p64
-        oid = u64(oid)
-        if tid is not None:
-            tid = u64(tid)
-        if before_tid is not None:
-            before_tid = u64(before_tid)
-        result = self._getObject(oid, tid, before_tid)
-        if result:
-            serial, next_serial, compression, checksum, data, data_serial = \
-                result
-            assert before_tid is None or next_serial is None or \
-                   before_tid <= next_serial
-            if serial is not None:
-                serial = p64(serial)
-            if next_serial is not None:
-                next_serial = p64(next_serial)
-            if data_serial is not None:
-                data_serial = p64(data_serial)
-            return serial, next_serial, compression, checksum, data, data_serial
+        r = self._getObject(u64(oid), tid and u64(tid),
+                            before_tid and u64(before_tid))
+        try:
+            serial, next_serial, compression, checksum, data, data_serial = r
+        except TypeError:
             # See if object exists at all
-        return self._getObject(oid) and False
+            return (tid or before_tid) and self.getLastObjectTID(oid) and False
+        return (util.p64(serial),
+                None if next_serial is None else util.p64(next_serial),
+                compression, checksum, data,
+                None if data_serial is None else util.p64(data_serial))
 
     def changePartitionTable(self, ptid, cell_list, reset=False):
         """Change a part of a partition table. The list of cells is
@@ -460,7 +456,7 @@ class DatabaseManager(object):
         area as well."""
         raise NotImplementedError
 
-    def getObjectHistory(self, oid, offset = 0, length = 1):
+    def getObjectHistory(self, oid, offset, length):
         """Return a list of serials and sizes for a given object ID.
         The length specifies the maximum size of such a list. Result starts
         with latest serial, and the list must be sorted in descending order.

neo/storage/database/mysqldb.py

@@ -282,6 +282,14 @@ class MySQLDatabaseManager(DatabaseManager):
                  % (self._getPartition(oid), oid, tid)) or all and \
                q("SELECT 1 FROM tobj WHERE tid=%d AND oid=%d" % (tid, oid))
 
+    def getLastObjectTID(self, oid):
+        oid = util.u64(oid)
+        r = self.query("SELECT tid FROM obj"
+                       " WHERE partition=%d AND oid=%d"
+                       " ORDER BY tid DESC LIMIT 1"
+                       % (self._getPartition(oid), oid))
+        return util.p64(r[0][0]) if r else None
+
     def _getObject(self, oid, tid=None, before_tid=None):
         q = self.query
         partition = self._getPartition(oid)
@@ -511,7 +519,7 @@ class MySQLDatabaseManager(DatabaseManager):
             oid_list = splitOIDField(tid, oids)
             return oid_list, user, desc, ext, bool(packed), util.p64(ttid)
 
-    def getObjectHistory(self, oid, offset = 0, length = 1):
+    def getObjectHistory(self, oid, offset, length):
         # FIXME: This method doesn't take client's current ransaction id as
         # parameter, which means it can return transactions in the future of
         # client's transaction.

neo/storage/database/sqlite.py

@@ -244,6 +244,14 @@ class SQLiteDatabaseManager(DatabaseManager):
                q("SELECT 1 FROM tobj WHERE tid=? AND oid=?",
                  (tid, oid)).fetchone()
 
+    def getLastObjectTID(self, oid):
+        oid = util.u64(oid)
+        r = self.query("SELECT tid FROM obj"
+                       " WHERE partition=? AND oid=?"
+                       " ORDER BY tid DESC LIMIT 1",
+                       (self._getPartition(oid), oid)).fetchone()
+        return r and util.p64(r[0])
+
     def _getObject(self, oid, tid=None, before_tid=None):
         q = self.query
         partition = self._getPartition(oid)
@@ -461,7 +469,7 @@ class SQLiteDatabaseManager(DatabaseManager):
             return splitOIDField(tid, oids), str(user), \
                 str(description), str(ext), packed, util.p64(ttid)
 
-    def getObjectHistory(self, oid, offset=0, length=1):
+    def getObjectHistory(self, oid, offset, length):
         # FIXME: This method doesn't take client's current transaction id as
         # parameter, which means it can return transactions in the future of
         # client's transaction.

neo/storage/transactions.py

@@ -274,9 +274,7 @@ class TransactionManager(object):
                 dump(oid), dump(ttid), dump(locking_tid))
             raise ConflictError(ZERO_TID)
         if previous_serial is None:
-            history_list = self._app.dm.getObjectHistory(oid)
-            if history_list:
-                previous_serial = history_list[0][0]
+            previous_serial = self._app.dm.getLastObjectTID(oid)
         if previous_serial is not None and previous_serial != serial:
             logging.info('Resolvable conflict on %r:%r',
                 dump(oid), dump(ttid))

neo/tests/storage/testTransactions.py

@@ -189,7 +189,7 @@ class TransactionManagerTests(NeoUnitTestBase):
         serial, obj = self._getObject(1)
         next_serial = self.getNextTID(serial)
         # try to store without the last revision
-        self.app.dm = Mock({'getObjectHistory': [next_serial]})
+        self.app.dm = Mock({'getLastObjectTID': next_serial})
         self.manager.register(uuid, tid)
         self.manager.storeTransaction(tid, *txn)
         self.assertRaises(ConflictError, self.manager.storeObject,