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, 18 deletions

diff --git a/lib/sqlalchemy/engine/events.py b/lib/sqlalchemy/engine/events.py
index 293c7afdd..ef760bb54 100644
--- a/lib/sqlalchemy/engine/events.py
+++ b/lib/sqlalchemy/engine/events.py
@@ -184,15 +184,11 @@ class ConnectionEvents(event.Events):
          :meth:`_engine.Connection.execute`.
         :param multiparams: Multiple parameter sets, a list of dictionaries.
         :param params: Single parameter set, a single dictionary.
-        :param execution_options: dictionary of per-execution execution
-         options passed along with the statement, if any.  This only applies to
-         the the SQLAlchemy 2.0 version of  :meth:`_engine.Connection.execute`
-         .   To
-         view all execution options associated with the connection, access the
-         :meth:`_engine.Connection.get_execution_options`
-         method to view the fixed
-         execution options dictionary, then consider elements within this local
-         dictionary to be unioned into that dictionary.
+        :param execution_options: dictionary of execution
+         options passed along with the statement, if any.  This is a merge
+         of all options that will be used, including those of the statement,
+         the connection, and those passed in to the method itself for
+         the 2.0 style of execution.
 
          .. versionadded: 1.4
 
@@ -231,15 +227,11 @@ class ConnectionEvents(event.Events):
          :meth:`_engine.Connection.execute`.
         :param multiparams: Multiple parameter sets, a list of dictionaries.
         :param params: Single parameter set, a single dictionary.
-        :param execution_options: dictionary of per-execution execution
-         options passed along with the statement, if any.  This only applies to
-         the the SQLAlchemy 2.0 version of  :meth:`_engine.Connection.execute`
-         .   To
-         view all execution options associated with the connection, access the
-         :meth:`_engine.Connection.get_execution_options`
-         method to view the fixed
-         execution options dictionary, then consider elements within this local
-         dictionary to be unioned into that dictionary.
+        :param execution_options: dictionary of execution
+         options passed along with the statement, if any.  This is a merge
+         of all options that will be used, including those of the statement,
+         the connection, and those passed in to the method itself for
+         the 2.0 style of execution.
 
          .. versionadded: 1.4