rearchitect reflection for batched performance

Rearchitected the schema reflection API to allow some dialects to make use
of high performing batch queries to reflect the schemas of many tables at
once using much fewer queries. The new performance features are targeted
first at the PostgreSQL and Oracle backends, and may be applied to any
dialect that makes use of SELECT queries against system catalog tables to
reflect tables (currently this omits the MySQL and SQLite dialects which
instead make use of parsing the "CREATE TABLE" statement, however these
dialects do not have a pre-existing performance issue with reflection. MS
SQL Server is still a TODO).

The new API is backwards compatible with the previous system, and should
require no changes to third party dialects to retain compatibility;
third party dialects can also opt into the new system by implementing
batched queries for schema reflection.

Along with this change is an updated reflection API that is fully
:pep:`484` typed, features many new methods and some changes.

Fixes: #4379
Change-Id: I897ec09843543aa7012bcdce758792ed3d415d08

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/typing.py b/lib/sqlalchemy/util/typing.py
index eb625e06e..4e76554c7 100644
--- a/lib/sqlalchemy/util/typing.py
+++ b/lib/sqlalchemy/util/typing.py
@@ -78,11 +78,13 @@ if typing.TYPE_CHECKING or compat.py38:
     from typing import Protocol as Protocol
     from typing import TypedDict as TypedDict
     from typing import Final as Final
+    from typing import final as final
 else:
     from typing_extensions import Literal as Literal  # noqa: F401
     from typing_extensions import Protocol as Protocol  # noqa: F401
     from typing_extensions import TypedDict as TypedDict  # noqa: F401
     from typing_extensions import Final as Final  # noqa: F401
+    from typing_extensions import final as final  # noqa: F401
 
 typing_get_args = get_args
 typing_get_origin = get_origin