Try to measure new style caching in the ORM, take two

Supercedes: If78fbb557c6f2cae637799c3fec2cbc5ac248aaf

Trying to see if by making the cache key memoized, we
still can have the older "identity" form of caching
which is the cheapest of all, at the same time as the
newer "cache key each time" version that is not nearly
as cheap; but still much cheaper than no caching at all.

Also needed is a per-execution update of _keymap when
we invoke from a cached select, so that Column objects
that are anonymous or otherwise adapted will match up.
this is analogous to the adaption of bound parameters
from the cache key.

Adds test coverage for the keymap / construct_params()
 changes related to caching.  Also hones performance
to a large extent for statement construction and
cache key generation.

Also includes a new memoized attribute
approach that vastly simplifies the previous approach
of "group_expirable_memoized_property" and finally
integrates cleanly with _clone(), _generate(), etc.
no more hardcoding of attributes is needed, as well
as that most _reset_memoization() calls are no longer
needed as the reset is inherent in a _generate() call;
this also has dramatic performance improvements.

Change-Id: I95c560ffcbfa30b26644999412fb6a385125f663

1 files changed, 2 insertions, 3 deletions

diff --git a/lib/sqlalchemy/sql/functions.py b/lib/sqlalchemy/sql/functions.py
index 6004f6b51..7973871f3 100644
--- a/lib/sqlalchemy/sql/functions.py
+++ b/lib/sqlalchemy/sql/functions.py
@@ -17,6 +17,7 @@ from . import sqltypes
 from . import util as sqlutil
 from .base import ColumnCollection
 from .base import Executable
+from .base import HasMemoized
 from .elements import _type_from_args
 from .elements import BinaryExpression
 from .elements import BindParameter
@@ -85,8 +86,6 @@ class FunctionElement(Executable, ColumnElement, FromClause):
 
     _has_args = False
 
-    _memoized_property = FromClause._memoized_property
-
     def __init__(self, *clauses, **kwargs):
         r"""Construct a :class:`.FunctionElement`.
 
@@ -141,7 +140,7 @@ class FunctionElement(Executable, ColumnElement, FromClause):
         col = self.label(None)
         return ColumnCollection(columns=[(col.key, col)])
 
-    @_memoized_property
+    @HasMemoized.memoized_attribute
     def clauses(self):
         """Return the underlying :class:`.ClauseList` which contains
         the arguments for this :class:`.FunctionElement`.