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, 15 insertions, 16 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/__init__.py b/lib/sqlalchemy/dialects/postgresql/__init__.py
index c2472fb55..85bbf8c5b 100644
--- a/lib/sqlalchemy/dialects/postgresql/__init__.py
+++ b/lib/sqlalchemy/dialects/postgresql/__init__.py
@@ -19,31 +19,16 @@ from .array import Any
 from .array import ARRAY
 from .array import array
 from .base import BIGINT
-from .base import BIT
 from .base import BOOLEAN
-from .base import BYTEA
 from .base import CHAR
-from .base import CIDR
-from .base import CreateEnumType
 from .base import DATE
 from .base import DOUBLE_PRECISION
-from .base import DropEnumType
-from .base import ENUM
 from .base import FLOAT
-from .base import INET
 from .base import INTEGER
-from .base import INTERVAL
-from .base import MACADDR
-from .base import MONEY
 from .base import NUMERIC
-from .base import OID
 from .base import REAL
-from .base import REGCLASS
 from .base import SMALLINT
 from .base import TEXT
-from .base import TIME
-from .base import TIMESTAMP
-from .base import TSVECTOR
 from .base import UUID
 from .base import VARCHAR
 from .dml import Insert
@@ -61,7 +46,21 @@ from .ranges import INT8RANGE
 from .ranges import NUMRANGE
 from .ranges import TSRANGE
 from .ranges import TSTZRANGE
-from ...util import compat
+from .types import BIT
+from .types import BYTEA
+from .types import CIDR
+from .types import CreateEnumType
+from .types import DropEnumType
+from .types import ENUM
+from .types import INET
+from .types import INTERVAL
+from .types import MACADDR
+from .types import MONEY
+from .types import OID
+from .types import REGCLASS
+from .types import TIME
+from .types import TIMESTAMP
+from .types import TSVECTOR
 
 # Alias psycopg also as psycopg_async
 psycopg_async = type(