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Path: ...!2.eu.feeder.erje.net!3.eu.feeder.erje.net!feeder.erje.net!fu-berlin.de!uni-berlin.de!not-for-mail From: Karsten Hilbert <Karsten.Hilbert@gmx.net> Newsgroups: comp.lang.python Subject: Re: psycopg2: proper positioning of .commit() within try: except: blocks Date: Sat, 7 Sep 2024 21:44:36 +0200 Lines: 69 Sender: <karsten.hilbert@gmx.net> Message-ID: <mailman.44.1725738290.2917.python-list@python.org> References: <Ztx1sZMGTnA3eLP1@hermes.hilbert.loc> <7cb50df2-9c76-477f-91c9-e149c7637104@aklaver.com> <ZtytJMhyvtExPxfF@hermes.hilbert.loc> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable X-Trace: news.uni-berlin.de xoeeCbNxFhxxwcCrVkKvrQdKn4id9nDEo+cD1+N1aGqQ== Cancel-Lock: sha1:sqPFge3q0XiS1kbdqsj+lobFSLE= sha256:Ly5nxvWmeljC3EpxfncVXgZ07gBudVePfeIYpUg3XG8= Return-Path: <karsten.hilbert@gmx.net> X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org Authentication-Results: mail.python.org; dkim=pass reason="2048-bit key; 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In fact in that codebase all transactions -- running concurrently or not -- are set to SERIALIZABLE. They are not psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT, for that matter. > > curs =3D conn.cursor() > > try: > > curs.execute(SOME_SQL) > > except PSYCOPG2-Exception: > > some logging being done, and, yes, I > > can safely inhibit propagation^1 > > finally: > > conn.commit() # will rollback, if SOME_SQL failed > > It will if you use with conn:, otherwise it up to you to do the rollback= () > > Are you are doing a rollback() in except PSYCOPG2-Exception: ? No I don't but - to my understanding - an ongoing transaction is being closed upon termination of the hosting connection. Unless .commit() is explicitely being issued somewhere in the code that closing of a transaction will amount to a ROLLBACK. In case of SQL having failed within a given transaction a COMMIT will fail-but-rollback, too (explicit ROLLBACK would succeed while a COMMIT would fail and, in-effect, roll back). IOW, when SOME_SQL has failed it won't matter that I close the connection with conn.commit() and it won't matter that conn.commit() runs a COMMIT on the database -- an open transaction having run that failed SQL will still roll back as if ROLLBACK had been issued. Or else my mental model is wrong. https://www.psycopg.org/docs/connection.html#connection.close In the particular case I was writing about the SQL itself succeeded but then the COMMIT failed due to serialization. I was wondering about where to best place any needed conn.commit(). My knee-jerk reaction was to then put it last in the try: block... All this is probably more related to Python than to PostgreSQL. Thanks, Karsten =2D- GPG 40BE 5B0E C98E 1713 AFA6 5BC0 3BEA AC80 7D4F C89B