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Introductory docs section on transaction control improved

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Added big fat warning about idle in transaction and reference to
set_session().
This commit is contained in:
Daniele Varrazzo 2011-06-08 14:38:57 +01:00
parent d2b28abced
commit d76d136b4f
2 changed files with 18 additions and 8 deletions
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2
doc/src/connection.rst
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@ -396,7 +396,7 @@ The ``connection`` class
.. warning:: .. warning::
By default, any query execution, including a simple :sql:`SELECT` By default, any query execution, including a simple :sql:`SELECT`
will start a transaction: for long-running program, if no further will start a transaction: for long-running programs, if no further
action is taken, the session will remain "idle in transaction", a action is taken, the session will remain "idle in transaction", a
condition non desiderable for several reasons (locks are held by condition non desiderable for several reasons (locks are held by
the session, tables bloat...). For long lived scripts, either the session, tables bloat...). For long lived scripts, either

24
doc/src/usage.rst
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@ -489,7 +489,7 @@ rounded to the nearest minute, with an error of up to 30 seconds.
versions use `psycopg2.extras.register_tstz_w_secs()`. versions use `psycopg2.extras.register_tstz_w_secs()`.
.. index:: Transaction, Begin, Commit, Rollback, Autocommit .. index:: Transaction, Begin, Commit, Rollback, Autocommit, Read only
.. _transactions-control: .. _transactions-control:
@ -503,7 +503,7 @@ The following database commands will be executed in the context of the same
transaction -- not only the commands issued by the first cursor, but the ones transaction -- not only the commands issued by the first cursor, but the ones
issued by all the cursors created by the same connection. Should any command issued by all the cursors created by the same connection. Should any command
fail, the transaction will be aborted and no further command will be executed fail, the transaction will be aborted and no further command will be executed
until a call to the `connection.rollback()` method. until a call to the `~connection.rollback()` method.
The connection is responsible to terminate its transaction, calling either the The connection is responsible to terminate its transaction, calling either the
`~connection.commit()` or `~connection.rollback()` method. Committed `~connection.commit()` or `~connection.rollback()` method. Committed
@ -516,13 +516,23 @@ It is possible to set the connection in *autocommit* mode: this way all the
commands executed will be immediately committed and no rollback is possible. A commands executed will be immediately committed and no rollback is possible. A
few commands (e.g. :sql:`CREATE DATABASE`, :sql:`VACUUM`...) require to be run few commands (e.g. :sql:`CREATE DATABASE`, :sql:`VACUUM`...) require to be run
outside any transaction: in order to be able to run these commands from outside any transaction: in order to be able to run these commands from
Psycopg, the session must be in autocommit mode. Read the documentation for Psycopg, the session must be in autocommit mode: you can use the
`connection.set_isolation_level()` to know how to change the commit mode. `~connection.autocommit` property (`~connection.set_isolation_level()` in
older versions).
.. note:: .. warning::
From version 2.4.2 you can use the `~connection.autocommit` property to By default even a simple :sql:`SELECT` will start a transaction: in
switch a connection in autocommit mode. long-running programs, if no further action is taken, the session will
remain "idle in transaction", a condition non desiderable for several
reasons (locks are held by the session, tables bloat...). For long lived
scripts, either ensure to terminate a transaction as soon as possible or
use an autocommit connection.
A few other transaction properties can be set session-wide by the
`!connection`: for instance it is possible to have read-only transactions or
change the isolation level. See the `~connection.set_session()` method for all
the details.
.. index:: .. index::