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, 9 insertions, 9 deletions

diff --git a/test/dialect/mysql/test_reflection.py b/test/dialect/mysql/test_reflection.py
index f414c9c37..846001347 100644
--- a/test/dialect/mysql/test_reflection.py
+++ b/test/dialect/mysql/test_reflection.py
@@ -33,9 +33,9 @@ from sqlalchemy import UniqueConstraint
 from sqlalchemy.dialects.mysql import base as mysql
 from sqlalchemy.dialects.mysql import reflection as _reflection
 from sqlalchemy.schema import CreateIndex
-from sqlalchemy.testing import assert_raises_message
 from sqlalchemy.testing import AssertsCompiledSQL
 from sqlalchemy.testing import eq_
+from sqlalchemy.testing import expect_raises_message
 from sqlalchemy.testing import expect_warnings
 from sqlalchemy.testing import fixtures
 from sqlalchemy.testing import is_
@@ -558,6 +558,10 @@ class ReflectionTest(fixtures.TestBase, AssertsCompiledSQL):
             )
 
     def test_skip_not_describable(self, metadata, connection):
+        """This test is the only one that test the _default_multi_reflect
+        behaviour with UnreflectableTableError
+        """
+
         @event.listens_for(metadata, "before_drop")
         def cleanup(*arg, **kw):
             with testing.db.begin() as conn:
@@ -579,14 +583,10 @@ class ReflectionTest(fixtures.TestBase, AssertsCompiledSQL):
             m.reflect(views=True, bind=conn)
         eq_(m.tables["test_t2"].name, "test_t2")
 
-        assert_raises_message(
-            exc.UnreflectableTableError,
-            "references invalid table",
-            Table,
-            "test_v",
-            MetaData(),
-            autoload_with=conn,
-        )
+        with expect_raises_message(
+            exc.UnreflectableTableError, "references invalid table"
+        ):
+            Table("test_v", MetaData(), autoload_with=conn)
 
     @testing.exclude("mysql", "<", (5, 0, 0), "no information_schema support")
     def test_system_views(self):