Barry Warsaw pushed to branch master at mailman / Mailman
Commits:
856d239e by Mark Sapiro at 2017-03-27T11:36:55-07:00
Implement SQLAlchemy pre-ping to detect dropped connections.
- - - - -
21385905 by Barry Warsaw at 2017-03-27T21:06:46+00:00
Merge branch 'sa-ping' into 'master'
Implement SQLAlchemy pre-ping to detect dropped connections.
Closes #313
See merge request !254
- - - - -
2 changed files:
- src/mailman/database/base.py
- src/mailman/docs/NEWS.rst
Changes:
=====================================
src/mailman/database/base.py
=====================================
--- a/src/mailman/database/base.py
+++ b/src/mailman/database/base.py
@@ -23,7 +23,7 @@ from mailman.config import config
from mailman.interfaces.database import IDatabase
from mailman.utilities.string import expand
from public import public
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, event, exc, select
from sqlalchemy.orm import sessionmaker
from zope.interface import implementer
@@ -107,3 +107,43 @@ class SABaseDatabase:
session = sessionmaker(bind=self.engine)
self.store = session()
self.store.commit()
+ # This is from the Dealing with Disconnects section at
+ # <http://docs.sqlalchemy.org/en/latest/core/pooling.html>. It
+ # establishes connection pinging to deal with lost connections due to
+ # database server restarts or other outside events.
+ #
+ # XXX This can all be removed once SQLAlchemy 1.2 is released, and we
+ # pass `pool_pre_ping=True` to create_engine().
+ @event.listens_for(self.engine, 'engine_connect') # noqa: E306
+ def ping_connection(connection, branch): # pragma: no cover
+ if branch:
+ # "branch" refers to a sub-connection of a connection;
+ # we don't want to bother pinging on these.
+ return
+ # Turn off "close with result". This flag is only used with
+ # "connectionless" execution, otherwise will be False in any case.
+ old_scwr = connection.should_close_with_result
+ connection.should_close_with_result = False
+ try:
+ # Run a SELECT 1. Use a core select() so that the SELECT of a
+ # scalar value without a table is appropriately formatted for
+ # the backend.
+ connection.scalar(select([1]))
+ except exc.DBAPIError as error:
+ # Catch SQLAlchemy's DBAPIError, which is a wrapper for the
+ # DBAPI's exception. It includes a .connection_invalidated
+ # attribute which specifies if this connection is a
+ # "disconnect" condition, which is based on inspection of the
+ # original exception by the dialect in use.
+ if error.connection_invalidated:
+ # Run the same SELECT again - the connection will
+ # re-validate itself and establish a new connection. The
+ # disconnect detection here also causes the whole
+ # connection pool to be invalidated so that all stale
+ # connections are discarded.
+ connection.scalar(select([1]))
+ else:
+ raise
+ finally:
+ # Restore "close with result".
+ connection.should_close_with_result = old_scwr
=====================================
src/mailman/docs/NEWS.rst
=====================================
--- a/src/mailman/docs/NEWS.rst
+++ b/src/mailman/docs/NEWS.rst
@@ -140,6 +140,9 @@ Command line
Database
--------
* MySQL is now an officially supported database. Given by Abhilash Raj.
+ * Fix a problem with tracebacks when a PostgreSQL database is power cycled
+ while Mailman is still running. This ports an upstream SQLAlchemy fix to
+ Mailman in lieu of a future SQLAlchemy 1.2 release. (Closes: #313)
Interfaces
----------
View it on GitLab:
https://gitlab.com/mailman/mailman/compare/775216d81ba75e00bfcbb482e075f473d12e99c4...213859054668ad64c0ea66f188beb1c239e4a0c0
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