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, 17 insertions, 0 deletions

diff --git a/lib/sqlalchemy/engine/create.py b/lib/sqlalchemy/engine/create.py
index e683b6297..4c912349e 100644
--- a/lib/sqlalchemy/engine/create.py
+++ b/lib/sqlalchemy/engine/create.py
@@ -435,6 +435,23 @@ def create_engine(url, **kwargs):
 
         .. versionadded:: 1.2.3
 
+    :param query_cache_size: size of the cache used to cache the SQL string
+     form of queries.  Defaults to zero, which disables caching.
+
+     Caching is accomplished on a per-statement basis by generating a
+     cache key that represents the statement's structure, then generating
+     string SQL for the current dialect only if that key is not present
+     in the cache.   All statements support caching, however some features
+     such as an INSERT with a large set of parameters will intentionally
+     bypass the cache.   SQL logging will indicate statistics for each
+     statement whether or not it were pull from the cache.
+
+     .. seealso::
+
+        ``engine_caching`` - TODO: this will be an upcoming section describing
+        the SQL caching system.
+
+     .. versionadded:: 1.4
 
     """  # noqa