- New features added to support engine/pool plugins with advanced

functionality.   Added a new "soft invalidate" feature to the
connection pool at the level of the checked out connection wrapper
as well as the :class:`._ConnectionRecord`.  This works similarly
to a modern pool invalidation in that connections aren't actively
closed, but are recycled only on next checkout; this is essentially
a per-connection version of that feature.  A new event
:class:`.PoolEvents.soft_invalidate` is added to complement it.
fixes #3379

- Added new flag
:attr:`.ExceptionContext.invalidate_pool_on_disconnect`.
Allows an error handler within :meth:`.ConnectionEvents.handle_error`
to maintain a "disconnect" condition, but to handle calling invalidate
on individual connections in a specific manner within the event.

- Added new event :class:`.DialectEvents.do_connect`, which allows
interception / replacement of when the :meth:`.Dialect.connect`
hook is called to create a DBAPI connection.  Also added
dialect plugin hooks :meth:`.Dialect.get_dialect_cls` and
:meth:`.Dialect.engine_created` which allow external plugins to
add events to existing dialects using entry points.
fixes #3355

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/sqlalchemy/engine/base.py b/lib/sqlalchemy/engine/base.py
index 5921ab9ba..af310c450 100644
--- a/lib/sqlalchemy/engine/base.py
+++ b/lib/sqlalchemy/engine/base.py
@@ -1254,6 +1254,8 @@ class Connection(Connectable):
             if context:
                 context.is_disconnect = self._is_disconnect
 
+        invalidate_pool_on_disconnect = True
+
         if self._reentrant_error:
             util.raise_from_cause(
                 exc.DBAPIError.instance(statement,
@@ -1316,6 +1318,11 @@ class Connection(Connectable):
                     sqlalchemy_exception.connection_invalidated = \
                         self._is_disconnect = ctx.is_disconnect
 
+                # set up potentially user-defined value for
+                # invalidate pool.
+                invalidate_pool_on_disconnect = \
+                    ctx.invalidate_pool_on_disconnect
+
             if should_wrap and context:
                 context.handle_dbapi_exception(e)
 
@@ -1340,7 +1347,8 @@ class Connection(Connectable):
                 del self._is_disconnect
                 if not self.invalidated:
                     dbapi_conn_wrapper = self.__connection
-                    self.engine.pool._invalidate(dbapi_conn_wrapper, e)
+                    if invalidate_pool_on_disconnect:
+                        self.engine.pool._invalidate(dbapi_conn_wrapper, e)
                     self.invalidate(e)
             if self.should_close_with_result:
                 self.close()