SteadyPg - hardened classic PyGreSQL connections.
Implements steady connections to a PostgreSQL database
using the classic (not DB-API 2 compliant) PyGreSQL API.
The connections are transparently reopened when they are
closed or the database connection has been lost or when
they are used more often than an optional usage limit.
Only connections which have been marked as being in a database
transaction with a begin() call will not be silently replaced.
A typical situation where database connections are lost
is when the database server or an intervening firewall is
shutdown and restarted for maintenance reasons. In such a
case, all database connections would become unusable, even
though the database service may be already available again.
The "hardened" connections provided by this module will
make the database connections immediately available again.
This results in a steady PostgreSQL connection that can be used
by PooledPg or PersistentPg to create pooled or persistent
connections to a PostgreSQL database in a threaded environment
such as the application server of "Webware for Python."
Note, however, that the connections themselves are not thread-safe.
For more information on PostgreSQL, see:
https://www.postgresql.org/
For more information on PyGreSQL, see:
http://www.pygresql.org
For more information on Webware for Python, see:
https://webwareforpython.github.io/w4py/
Usage:
You can use the class SteadyPgConnection in the same way as you
would use the class DB from the classic PyGreSQL API module db.
The only difference is that you may specify a usage limit as the
first parameter when you open a connection (set it to None
if you prefer unlimited usage), and an optional list of commands
that may serve to prepare the session as the second parameter,
and you can specify whether is is allowed to close the connection
(by default this is true). When the connection to the PostgreSQL
database is lost or has been used too often, it will be automatically
reset, without further notice.
from dbutils.steady_pg import SteadyPgConnection
db = SteadyPgConnection(10000, ["set datestyle to german"],
host=..., dbname=..., user=..., ...)
...
result = db.query('...')
...
db.close()
Ideas for improvement:
* Alternatively to the maximum number of uses,
implement a maximum time to live for connections.
* Optionally log usage and loss of connection.
Copyright, credits and license:
* Contributed as supplement for Webware for Python and PyGreSQL
by Christoph Zwerschke in September 2005
Licensed under the MIT license.
