- for #3230, scale back the check to only look at columns that

already have more than one ForeignKeyConstraint referring to them.
This limits the check to what we hope is the most common case,
but we benefit that the memory and config-time impact is scaled back
dramatically.

diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index 4a6159144a9c7b2783d5b3de56d26dadcd435411..86f1b3f827d34f1fe226cecd0c6db649d6f94eb8 100644 (file)
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -2521,32 +2521,37 @@ class JoinCondition(object):
         self.secondary_synchronize_pairs = \
             self._deannotate_pairs(secondary_sync_pairs)
 
-    _track_sync_targets = weakref.WeakKeyDictionary()
+    _track_overlapping_sync_targets = weakref.WeakKeyDictionary()
 
     def _warn_for_conflicting_sync_targets(self):
         if not self.support_sync:
             return
 
-        # totally complex code that takes place for virtually all
-        # relationships, detecting an incredibly rare edge case,
-        # and even then, all just to emit a warning.
         # we would like to detect if we are synchronizing any column
         # pairs in conflict with another relationship that wishes to sync
-        # an entirely different column to the same target.  This is typically
-        # when using complex overlapping composite foreign keys.
+        # an entirely different column to the same target.   This is a
+        # very rare edge case so we will try to minimize the memory/overhead
+        # impact of this check
         for from_, to_ in [
-            (from_, to_)
-            for (from_, to_) in self.synchronize_pairs
+            (from_, to_) for (from_, to_) in self.synchronize_pairs
         ] + [
-            (from_, to_) for
-            (from_, to_) in self.secondary_synchronize_pairs
+            (from_, to_) for (from_, to_) in self.secondary_synchronize_pairs
         ]:
-            if to_ not in self._track_sync_targets:
-                self._track_sync_targets[to_] = weakref.WeakKeyDictionary(
-                    {self.prop: from_})
+            # save ourselves a ton of memory and overhead by only
+            # considering columns that are subject to a overlapping
+            # FK constraints at the core level.   This condition can arise
+            # if multiple relationships overlap foreign() directly, but
+            # we're going to assume it's typically a ForeignKeyConstraint-
+            # level configuration that benefits from this warning.
+            if len(to_.foreign_keys) < 2:
+                continue
+
+            if to_ not in self._track_overlapping_sync_targets:
+                self._track_overlapping_sync_targets[to_] = \
+                    weakref.WeakKeyDictionary({self.prop: from_})
             else:
                 other_props = []
-                prop_to_from = self._track_sync_targets[to_]
+                prop_to_from = self._track_overlapping_sync_targets[to_]
                 for pr, fr_ in prop_to_from.items():
                     if pr.mapper in mapperlib._mapper_registry and \
                         fr_ is not from_ and \
@@ -2568,7 +2573,7 @@ class JoinCondition(object):
                                 for (pr, fr_) in other_props)
                         )
                     )
-                self._track_sync_targets[to_][self.prop] = from_
+                self._track_overlapping_sync_targets[to_][self.prop] = from_
 
     @util.memoized_property
     def remote_columns(self):