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SteadyPg - hardened classic PyGreSQL connections.
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Implements steady connections to a PostgreSQL database
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using the classic (not DB-API 2 compliant) PyGreSQL API.
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The connections are transparently reopened when they are
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closed or the database connection has been lost or when
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they are used more often than an optional usage limit.
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Only connections which have been marked as being in a database
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transaction with a begin() call will not be silently replaced.
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A typical situation where database connections are lost
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is when the database server or an intervening firewall is
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shutdown and restarted for maintenance reasons. In such a
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case, all database connections would become unusable, even
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though the database service may be already available again.
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The "hardened" connections provided by this module will
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make the database connections immediately available again.
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This results in a steady PostgreSQL connection that can be used
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by PooledPg or PersistentPg to create pooled or persistent
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connections to a PostgreSQL database in a threaded environment
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such as the application server of "Webware for Python."
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Note, however, that the connections themselves are not thread-safe.
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For more information on PostgreSQL, see:
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https://www.postgresql.org/
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For more information on PyGreSQL, see:
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http://www.pygresql.org
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For more information on Webware for Python, see:
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https://webwareforpython.github.io/w4py/
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Usage:
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You can use the class SteadyPgConnection in the same way as you
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would use the class DB from the classic PyGreSQL API module db.
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The only difference is that you may specify a usage limit as the
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first parameter when you open a connection (set it to None
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if you prefer unlimited usage), and an optional list of commands
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that may serve to prepare the session as the second parameter,
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and you can specify whether is is allowed to close the connection
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(by default this is true). When the connection to the PostgreSQL
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database is lost or has been used too often, it will be automatically
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reset, without further notice.
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from dbutils.steady_pg import SteadyPgConnection
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db = SteadyPgConnection(10000, ["set datestyle to german"],
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host=..., dbname=..., user=..., ...)
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...
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result = db.query('...')
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...
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db.close()
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Ideas for improvement:
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* Alternatively to the maximum number of uses,
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implement a maximum time to live for connections.
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* Optionally log usage and loss of connection.
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Copyright, credits and license:
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* Contributed as supplement for Webware for Python and PyGreSQL
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by Christoph Zwerschke in September 2005
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Licensed under the MIT license.
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é )ÚDBé )Ú __version__c @ s e Zd ZdZdS )Ú SteadyPgErrorzGeneral SteadyPg error.N©Ú__name__Ú
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__module__Ú __qualname__Ú__doc__© r r úHd:\z\workplace\vscode\pyvenv\venv\Lib\site-packages\dbutils/steady_pg.pyr R s r c @ s e Zd ZdZdS )ÚInvalidConnectionz Database connection is invalid.Nr r r r r r V s r c @ s e Zd ZdZeZd"ddZdd Zdd Zd
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dd Z dd Z dd Z d#ddZd$ddZd%ddZd&ddZd d Zd d Zd d! ZdS )'ÚSteadyPgConnectionaû Class representing steady connections to a PostgreSQL database.
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Underlying the connection is a classic PyGreSQL pg API database
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connection which is reset if the connection is lost or used too often.
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Thus the resulting connection is steadier ("tough and self-healing").
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If you want the connection to be persistent in a threaded environment,
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then you should not deal with this class directly, but use either the
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PooledPg module or the PersistentPg module to get the connections.
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NTc O sf d| _ d| _|dkrd}t|ts*td|| _|| _|| _t||| _ d| _ d| _|
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¡ d| _ dS )aÅ Create a "tough" PostgreSQL connection.
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maxusage: maximum usage limit for the underlying PyGreSQL connection
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(number of uses, 0 or None means unlimited usage)
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When this limit is reached, the connection is automatically reset.
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setsession: optional list of SQL commands that may serve to prepare
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the session, e.g. ["set datestyle to ...", "set time zone ..."]
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closeable: if this is set to false, then closing the connection will
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be silently ignored, but by default the connection can be closed
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args, kwargs: the parameters that shall be used to establish
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the PostgreSQL connections with PyGreSQL using pg.DB()
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NTr z$'maxusage' must be an integer value.F) Ú_conÚ_closedÚ
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isinstanceÚbaseintÚ TypeErrorÚ _maxusageÚ_setsession_sqlÚ
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_closeableÚ PgConnectionÚ _transactionÚ _setsessionÚ_usage)ÚselfZmaxusageZ
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setsessionZ closeableÚargsÚkwargsr r r Ú__init__h s
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zSteadyPgConnection.__init__c C s | ¡ | S )z9Enter the runtime context. This will start a transaction.)Úbegin©r r r r Ú __enter__ s z SteadyPgConnection.__enter__c G s: |d dkr.|d dkr.|d dkr.| ¡ n| ¡ dS )z8Exit the runtime context. This will end the transaction.r Nr é )ÚcommitÚrollback)r Úexcr r r Ú__exit__ s $
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zSteadyPgConnection.__exit__c C s" | j r | j D ]}| j |¡ q dS )z1Execute the SQL commands for session preparation.N)r r Úquery)r Úsqlr r r r s
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z SteadyPgConnection._setsessionc C s: | j s6z| j ¡ W n tk
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r( Y nX d| _d| _ dS )z§Close the tough connection.
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You can always close a tough connection with this method
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and it will not complain if you close it more than once.
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FTN)r r ÚcloseÚ Exceptionr r r r r Ú_close s zSteadyPgConnection._closec C s" | j r| ¡ n| jr | ¡ dS )a] Close the tough connection.
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You are allowed to close a tough connection by default
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and it will not complain if you close it more than once.
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You can disallow closing connections by setting
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the closeable parameter to something false. In this case,
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closing tough connections will be silently ignored.
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N)r r+ r Úresetr r r r r) ¨ s
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zSteadyPgConnection.closec C st z| j ¡ W nF tk
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rN Y nX Y n X d| _d| _| ¡ d| _dS )ziReopen the tough connection.
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It will not complain if the connection cannot be reopened.
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Fr$ r N) r Úreopenr* Z _transcationr r' r r r r r r r r- · s zSteadyPgConnection.reopenc C s z"| j ¡ d| _| ¡ d| _W nX tk
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rn Y nX Y nX Y nX dS )z«Reset the tough connection.
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If a reset is not possible, tries to reopen the connection.
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It will not complain if the connection is already closed.
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Fr N)r r, r r r r* r- r$ r r r r r, Ë s
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zSteadyPgConnection.resetc C sP d| _ z | jj}W n$ tk
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r6 | j |p.d¡ Y S X |rF||dS | S dS )zBegin a transaction.Tr ©r( N)r r r ÚAttributeErrorr' )r r( r r r r r ß s
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zSteadyPgConnection.beginc C sP d| _ z | jj}W n$ tk
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r6 | j |p.d¡ Y S X |rF||dS | S dS )ú Commit the current transaction.FÚendr. N)r r r1 r/ r' )r r( r1 r r r r1 í s
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zSteadyPgConnection.endc C sP d| _ z | jj}W n$ tk
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r6 | j |p.d¡ Y S X |rF||dS | S dS )z!Rollback the current transaction.Fr$ r. N)r r r$ r/ r' )r r( r$ r r r r$ s
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zSteadyPgConnection.rollbackc s fdd}|S )a Return a "tough" version of a connection class method.
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The tough version checks whether the connection is bad (lost)
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and automatically and transparently tries to reset the connection
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if this is the case (for instance, the database has been restarted).
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r |rxd_ n jjjr n ¡ | |}Y nX jd7 _|S )NFr ) r r ÚdbÚstatusr r r/ r* r, )r r Z transactionÚresult©Úmethodr r r Ú tough_method s.
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Inherit the members of the standard connection class.
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Some methods are made "tougher" than in the standard version.
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r Y nX dS )z Delete the steady connection.N)r+ r* r r r r Ú__del__C s zSteadyPgConnection.__del__)NNT)N)N)N)N)r r r r
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