callcount reductions and refinement for cached queries

This commit includes that we've removed the "_orm_query"
attribute from compile state as well as query context.
The attribute created reference cycles and also added
method call overhead.    As part of this change,
the interface for ORMExecuteState changes a bit, as well
as the interface for the horizontal sharding extension
which now deprecates the "query_chooser" callable
in favor of "execute_chooser", which receives the contextual
object.  This will also work more nicely when we implement
the new execution path for bulk updates and deletes.

Pre-merge execution options for statement, connection,
arguments all up front in Connection.  that way they
can be passed to the before_execute / after_execute events,
and the ExecutionContext doesn't have to merge as second
time.   Core execute is pretty close to 1.3 now.

baked wasn't using the new one()/first()/one_or_none() methods,
fixed that.

Convert non-buffered cursor strategy to be a stateless
singleton.  inline all the paths by which the strategy
gets chosen, oracle and SQL Server dialects make use of the
already-invoked post_exec() hook to establish the alternate
strategies, and this is actually much nicer than it was before.

Add caching to mapper instance processor for getters.

Identified a reference cycle per query that was showing
up as a lot of gc cleanup, fixed that.

After all that, performance not budging much.  Even
test_baked_query now runs with significantly fewer function
calls than 1.3, still 40% slower.

Basically something about the new patterns just makes
this slower and while I've walked a whole bunch of them
back, it hardly makes a dent.  that said, the performance
issues are relatively small, in the 20-40% time increase
range, and the new caching feature
does provide for regular ORM and Core queries that
are cached, and they are faster than non-cached.

Change-Id: I7b0b0d8ca550c05f79e82f75cd8eff0bbfade053

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/sqlalchemy/util/langhelpers.py b/lib/sqlalchemy/util/langhelpers.py
index f6fefc244..52debc517 100644
--- a/lib/sqlalchemy/util/langhelpers.py
+++ b/lib/sqlalchemy/util/langhelpers.py
@@ -942,6 +942,10 @@ class HasMemoized(object):
         for elem in self._memoized_keys:
             assert elem not in self.__dict__
 
+    def _set_memoized_attribute(self, key, value):
+        self.__dict__[key] = value
+        self._memoized_keys |= {key}
+
     class memoized_attribute(object):
         """A read-only @property that is only evaluated once."""
 
@@ -1260,15 +1264,20 @@ class classproperty(property):
 class hybridproperty(object):
     def __init__(self, func):
         self.func = func
+        self.clslevel = func
 
     def __get__(self, instance, owner):
         if instance is None:
-            clsval = self.func(owner)
+            clsval = self.clslevel(owner)
             clsval.__doc__ = self.func.__doc__
             return clsval
         else:
             return self.func(instance)
 
+    def classlevel(self, func):
+        self.clslevel = func
+        return self
+
 
 class hybridmethod(object):
     """Decorate a function as cls- or instance- level."""