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, 4 insertions, 10 deletions

diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index bb606a4d6..6415d4b37 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -470,12 +470,7 @@ class CompileState(object):
             return None
 
     @classmethod
-    def _get_plugin_compile_state_cls(cls, statement, plugin_name):
-        statement_plugin_name = statement._propagate_attrs.get(
-            "compile_state_plugin", "default"
-        )
-        if statement_plugin_name != plugin_name:
-            return None
+    def _get_plugin_class_for_plugin(cls, statement, plugin_name):
         try:
             return cls.plugins[(plugin_name, statement.__visit_name__)]
         except KeyError:
@@ -607,9 +602,6 @@ class Executable(Generative):
     def _disable_caching(self):
         self._cache_enable = HasCacheKey()
 
-    def _get_plugin_compile_state_cls(self, plugin_name):
-        return CompileState._get_plugin_compile_state_cls(self, plugin_name)
-
     @_generative
     def options(self, *options):
         """Apply options to this statement.
@@ -735,7 +727,9 @@ class Executable(Generative):
                 "to execute this construct." % label
             )
             raise exc.UnboundExecutionError(msg)
-        return e._execute_clauseelement(self, multiparams, params)
+        return e._execute_clauseelement(
+            self, multiparams, params, util.immutabledict()
+        )
 
     @util.deprecated_20(
         ":meth:`.Executable.scalar`",