Optimize loadBefore for tests.

CHANGES.rst

@@ -7,7 +7,11 @@
 
 - Eliminate runtime dependency on ZEO. See :issue:`293`.
 
-- Fix a rare race condition allocating OIDs on MySQL. See :issue:`283`.
+- Fix a rare race condition allocating OIDs on MySQL. See
+  :issue:`283`.
+
+- Optimize the ``loadBefore`` method. It appears to be mostly used in
+  the tests.
 
 3.0a6 (2019-07-29)
 ==================

src/relstorage/storage/__init__.py

@@ -137,9 +137,6 @@ class RelStorage(LegacyMethodsMixin,
 
     _oids = ReadOnlyOIDs()
 
-
-    __initting = True
-
     # Attributes in our dictionary that shouldn't have stale()/no_longer_stale()
     # called on them. At this writing, it's just the type object.
     _STALE_IGNORED_ATTRS = (
@@ -264,17 +261,6 @@ def __init__(self, adapter, name=None, create=None,
             storer = BlobStorer(self.blobhelper, self._store_connection)
             copy_storage_methods(self, storer)
 
-        self.__initting = False
-
-    # __setattr__ is here during refactoring to help us make sure we're setting what we
-    # want to set.
-    # XXX: Remove before release.
-    def __setattr__(self, name, value):
-        # undo is special cased for reltestbase._make_readonly
-        if not self.__initting and name not in dir(self) and name != 'undo':
-            raise AttributeError("Cannot set %s" % name)
-        object.__setattr__(self, name, value)
-
     def __repr__(self):
         return "<%s at %x keep_history=%s phase=%r cache=%r>" % (
             self.__class__.__name__,

src/relstorage/storage/load.py

@@ -28,6 +28,7 @@
 
 from ZODB.utils import p64 as int64_to_8bytes
 from ZODB.utils import u64 as bytes8_to_int64
+from ZODB.utils import maxtid
 
 from relstorage.cache.interfaces import CacheConsistencyError
 from .util import storage_method
@@ -187,12 +188,32 @@ def loadSerial(self, oid, serial):
     @storage_method
     @Metric(method=True, rate=0.1)
     def loadBefore(self, oid, tid):
-        """Return the most recent revision of oid before tid committed."""
+        """
+        Return the most recent revision of oid before tid committed.
+        """
+        if tid is maxtid or tid == maxtid:
+            # This is probably from ZODB.utils.load_current(), which
+            # is really trying to just get the current state of the
+            # object. So return that, formatted in the way this method
+            # returns it: (state, tid of state, tid_after_state) where
+            # tid_after_state will naturally be None
+            return self.load(oid) + (None,)
         oid_int = bytes8_to_int64(oid)
 
+        # TODO: This makes three separate queries, and also bypasses the cache.
+        # We should be able to fix at least the multiple queries.
+
         if self.store_connection:
             # Allow loading data from later transactions
             # for conflict resolution.
+
+            # XXX: This doesn't seem to be used in conflict
+            # resolution. ZODB.ConflictResolution.tryToResolveConflict
+            # calls loadSerial(); About the only call in ZODB to
+            # loadBefore() is from BlobStorage.undo() (which
+            # RelStorage does not extend). Mixing and matching calls
+            # between connections using different isolation levels
+            # isn't great. Can we stop doing this?
             cursor = self.store_connection.cursor
         else:
             cursor = self.load_connection.cursor