perf tweaks

- avoid abc checks in distill_20
- ColumnEntity subclasses are unique to their compile state and
have no querycontext specific state.  They can do a simple memoize of their
fetch_column without using attributes, and they can memoize their
_getter() too so that it goes into the cache, just like
instance_processor() does.
- unify ORMColumnEntity and RawColumnEntity for the row processor part,
add some test coverage for the case where it is used in a from_statement
- do a faster generate if there are no memoized entries
- query._params is always immutabledict
Change-Id: I1e2dfe607a1749b5b434fc11f9348ee631501dfa

1 files changed, 8 insertions, 2 deletions

diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index 5f2ce8f14..4c603b6dd 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -495,8 +495,14 @@ class Generative(HasMemoized):
 
     def _generate(self):
         skip = self._memoized_keys
-        s = self.__class__.__new__(self.__class__)
-        s.__dict__ = {k: v for k, v in self.__dict__.items() if k not in skip}
+        cls = self.__class__
+        s = cls.__new__(cls)
+        if skip:
+            s.__dict__ = {
+                k: v for k, v in self.__dict__.items() if k not in skip
+            }
+        else:
+            s.__dict__ = self.__dict__.copy()
         return s