Convert execution to move through Session

This patch replaces the ORM execution flow with a
single pathway through Session.execute() for all queries,
including Core and ORM.

Currently included is full support for ORM Query,
Query.from_statement(), select(), as well as the
baked query and horizontal shard systems.  Initial
changes have also been made to the dogpile caching
example, which like baked query makes use of a
new ORM-specific execution hook that replaces the
use of both QueryEvents.before_compile() as well
as Query._execute_and_instances() as the central
ORM interception hooks.

select() and Query() constructs alike can be passed to
Session.execute() where they will return ORM
results in a Results object.   This API is currently
used internally by Query.   Full support for
Session.execute()->results to behave in a fully
2.0 fashion will be in later changesets.

bulk update/delete with ORM support will also
be delivered via the update() and delete()
constructs, however these have not yet been adapted
to the new system and may follow in a subsequent
update.

Performance is also beginning to lag as of this
commit and some previous ones.   It is hoped that
a few central functions such as the coercions
functions can be rewritten in C to re-gain
performance.  Additionally, query caching
is now available and some subsequent patches
will attempt to cache more of the per-execution
work from the ORM layer, e.g. column getters
and adapters.

This patch also contains initial "turn on" of the
caching system enginewide via the query_cache_size
parameter to create_engine(). Still defaulting at
zero for "no caching".   The caching system still
needs adjustments in order to gain adequate performance.

Change-Id: I047a7ebb26aa85dc01f6789fac2bff561dcd555d

1 files changed, 23 insertions, 0 deletions

diff --git a/examples/performance/short_selects.py b/examples/performance/short_selects.py
index db8ab8789..38bc1508a 100644
--- a/examples/performance/short_selects.py
+++ b/examples/performance/short_selects.py
@@ -82,6 +82,29 @@ def test_orm_query_cols_only(n):
         ).one()
 
 
+cache = {}
+
+
+@Profiler.profile
+def test_cached_orm_query(n):
+    """test new style cached queries of the full entity."""
+    s = Session(bind=engine)
+    for id_ in random.sample(ids, n):
+        stmt = s.query(Customer).filter(Customer.id == id_)
+        s.execute(stmt, execution_options={"compiled_cache": cache}).one()
+
+
+@Profiler.profile
+def test_cached_orm_query_cols_only(n):
+    """test new style cached queries of the full entity."""
+    s = Session(bind=engine)
+    for id_ in random.sample(ids, n):
+        stmt = s.query(
+            Customer.id, Customer.name, Customer.description
+        ).filter(Customer.id == id_)
+        s.execute(stmt, execution_options={"compiled_cache": cache}).one()
+
+
 @Profiler.profile
 def test_baked_query(n):
     """test a baked query of the full entity."""