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, 16 insertions, 3 deletions

diff --git a/test/sql/test_resultset.py b/test/sql/test_resultset.py
index 0eff94635..6428b7dbe 100644
--- a/test/sql/test_resultset.py
+++ b/test/sql/test_resultset.py
@@ -579,7 +579,7 @@ class CursorResultTest(fixtures.TablesTest):
             lambda r: r._getter("user"),
             lambda r: r.keys(),
             lambda r: r.columns("user"),
-            lambda r: r.cursor_strategy.fetchone(r),
+            lambda r: r.cursor_strategy.fetchone(r, r.cursor),
         ]:
             trans = conn.begin()
             result = conn.execute(users.insert(), user_id=1)
@@ -2130,8 +2130,21 @@ class AlternateCursorResultTest(fixtures.TablesTest):
         self.table = self.tables.test
 
         class ExcCtx(default.DefaultExecutionContext):
-            def get_result_cursor_strategy(self, result):
-                return cls.create(result)
+            def post_exec(self):
+                if cls is _cursor.CursorFetchStrategy:
+                    pass
+                elif cls is _cursor.BufferedRowCursorFetchStrategy:
+                    self.cursor_fetch_strategy = cls(
+                        self.cursor, self.execution_options
+                    )
+                elif cls is _cursor.FullyBufferedCursorFetchStrategy:
+                    self.cursor_fetch_strategy = cls(
+                        self.cursor,
+                        self.cursor.description,
+                        self.cursor.fetchall(),
+                    )
+                else:
+                    assert False
 
         self.patcher = patch.object(
             self.engine.dialect, "execution_ctx_cls", ExcCtx