Deprecate engine-wise ss cursors; repair mariadbconnector

The server_side_cursors engine-wide feature relies upon
regexp parsing of statements a well as general guessing as
to when the feature should be used.   This is not within the
2.0 way of doing things and should be removed.

Additionally, mariadbconnector defaults to unbuffered cursors;
add new cursor hooks so that mariadbconnector can specify
buffered or unbuffered cursors without too much difficulty.
This will also correctly default mariadbconnector to buffered
cursors which should repair the segfaults we've been getting.

Try to restore the assert_raises that was removed in
5b6dfc0c38bf1f01da4b8 to see if mariadbconnector segfaults
are resolved.

Change-Id: I77f1c972c742e40694972f578140bb0cac8c39eb

1 files changed, 30 insertions, 1 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 3ef87620f..5e81586b4 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -112,6 +112,34 @@ The CREATE TABLE for the above :class:`_schema.Table` object would be:
            PRIMARY KEY (id)
        )
 
+.. _postgresql_ss_cursors:
+
+Server Side Cursors
+-------------------
+
+Server-side cursor support is available for the psycopg2, asyncpg
+dialects and may also be available in others.
+
+Server side cursors are enabled on a per-statement basis by using the
+:paramref:`.Connection.execution_options.stream_results` connection execution
+option::
+
+    with engine.connect() as conn:
+        result = conn.execution_options(stream_resuls=True).execute(text("select * from table"))
+
+Note that some kinds of SQL statements may not be supported with
+server side cursors; generally, only SQL statements that return rows should be
+used with this option.
+
+.. deprecated:: 1.4  The dialect-level server_side_cursors flag is deprecated
+   and will be removed in a future release.  Please use the
+   :paramref:`_engine.Connection.stream_results` execution option for
+   unbuffered cursor support.
+
+.. seealso::
+
+    :ref:`engine_stream_results`
+
 .. _postgresql_isolation_level:
 
 Transaction Isolation Level
@@ -1075,7 +1103,8 @@ E.g.::
     )
 
 
-"""
+"""  # noqa E501
+
 from collections import defaultdict
 import datetime as dt
 import re