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

3 files changed, 23 insertions, 38 deletions

diff --git a/lib/sqlalchemy/dialects/mssql/base.py b/lib/sqlalchemy/dialects/mssql/base.py
index 3345d555f..5e0704597 100644
--- a/lib/sqlalchemy/dialects/mssql/base.py
+++ b/lib/sqlalchemy/dialects/mssql/base.py
@@ -1529,8 +1529,7 @@ class MSExecutionContext(default.DefaultExecutionContext):
         elif (
             self.isinsert or self.isupdate or self.isdelete
         ) and self.compiled.returning:
-            fbcr = _cursor.FullyBufferedCursorFetchStrategy
-            self._result_strategy = fbcr.create_from_buffer(
+            self.cursor_fetch_strategy = _cursor.FullyBufferedCursorFetchStrategy(  # noqa
                 self.cursor, self.cursor.description, self.cursor.fetchall()
             )
 
@@ -1571,14 +1570,6 @@ class MSExecutionContext(default.DefaultExecutionContext):
             except Exception:
                 pass
 
-    def get_result_cursor_strategy(self, result):
-        if self._result_strategy:
-            return self._result_strategy
-        else:
-            return super(MSExecutionContext, self).get_result_cursor_strategy(
-                result
-            )
-
 
 class MSSQLCompiler(compiler.SQLCompiler):
     returning_precedes_values = True
diff --git a/lib/sqlalchemy/dialects/oracle/cx_oracle.py b/lib/sqlalchemy/dialects/oracle/cx_oracle.py
index c61a1cc0a..4aae059dd 100644
--- a/lib/sqlalchemy/dialects/oracle/cx_oracle.py
+++ b/lib/sqlalchemy/dialects/oracle/cx_oracle.py
@@ -696,6 +696,27 @@ class OracleExecutionContext_cx_oracle(OracleExecutionContext):
 
         self._generate_cursor_outputtype_handler()
 
+    def post_exec(self):
+        if self.compiled and self.out_parameters and self.compiled.returning:
+            # create a fake cursor result from the out parameters. unlike
+            # get_out_parameter_values(), the result-row handlers here will be
+            # applied at the Result level
+            returning_params = [
+                self.dialect._returningval(self.out_parameters["ret_%d" % i])
+                for i in range(len(self.out_parameters))
+            ]
+
+            fetch_strategy = _cursor.FullyBufferedCursorFetchStrategy(
+                self.cursor,
+                [
+                    (getattr(col, "name", col.anon_label), None)
+                    for col in self.compiled.returning
+                ],
+                initial_buffer=[tuple(returning_params)],
+            )
+
+            self.cursor_fetch_strategy = fetch_strategy
+
     def create_cursor(self):
         c = self._dbapi_connection.cursor()
         if self.dialect.arraysize:
@@ -714,29 +735,6 @@ class OracleExecutionContext_cx_oracle(OracleExecutionContext):
             for name in out_param_names
         ]
 
-    def get_result_cursor_strategy(self, result):
-        if self.compiled and self.out_parameters and self.compiled.returning:
-            # create a fake cursor result from the out parameters. unlike
-            # get_out_parameter_values(), the result-row handlers here will be
-            # applied at the Result level
-            returning_params = [
-                self.dialect._returningval(self.out_parameters["ret_%d" % i])
-                for i in range(len(self.out_parameters))
-            ]
-
-            return _cursor.FullyBufferedCursorFetchStrategy(
-                result.cursor,
-                [
-                    (getattr(col, "name", col.anon_label), None)
-                    for col in result.context.compiled.returning
-                ],
-                initial_buffer=[tuple(returning_params)],
-            )
-        else:
-            return super(
-                OracleExecutionContext_cx_oracle, self
-            ).get_result_cursor_strategy(result)
-
 
 class OracleDialect_cx_oracle(OracleDialect):
     execution_ctx_cls = OracleExecutionContext_cx_oracle
diff --git a/lib/sqlalchemy/dialects/postgresql/psycopg2.py b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
index 9585dd467..a9408bcb0 100644
--- a/lib/sqlalchemy/dialects/postgresql/psycopg2.py
+++ b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
@@ -592,13 +592,9 @@ class PGExecutionContext_psycopg2(PGExecutionContext):
         ident = "c_%s_%s" % (hex(id(self))[2:], hex(_server_side_id())[2:])
         return self._dbapi_connection.cursor(ident)
 
-    def get_result_cursor_strategy(self, result):
+    def post_exec(self):
         self._log_notices(self.cursor)
 
-        return super(PGExecutionContext, self).get_result_cursor_strategy(
-            result
-        )
-
     def _log_notices(self, cursor):
         # check also that notices is an iterable, after it's already
         # established that we will be iterating through it.  This is to get