From: Mike Bayer Date: Tue, 18 Jun 2013 03:12:04 +0000 (-0400) Subject: fix up the isolation level docs which were a mess X-Git-Tag: rel_0_8_2~40 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2bb1a3f8b4329e8aa026114daf95a8e1afc6a1c6;p=thirdparty%2Fsqlalchemy%2Fsqlalchemy.git fix up the isolation level docs which were a mess --- diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py index 49f097c580..8c9af5bcf6 100644 --- a/lib/sqlalchemy/dialects/postgresql/base.py +++ b/lib/sqlalchemy/dialects/postgresql/base.py @@ -41,24 +41,40 @@ case. To force the usage of RETURNING by default off, specify the flag ``implicit_returning=False`` to :func:`.create_engine`. +.. _postgresql_isolation_level: + Transaction Isolation Level --------------------------- -:func:`.create_engine` accepts an ``isolation_level`` parameter which results -in the command ``SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL -`` being invoked for every new connection. Valid values for this -parameter include ``READ COMMITTED``, ``READ UNCOMMITTED``, ``REPEATABLE READ``, -and ``SERIALIZABLE``:: +All Postgresql dialects support setting of transaction isolation level +both via a dialect-specific parameter ``isolation_level`` +accepted by :func:`.create_engine`, +as well as the ``isolation_level`` argument as passed to :meth:`.Connection.execution_options`. +When using a non-psycopg2 dialect, this feature works by issuing the +command ``SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL +`` for each new connection. + +To set isolation level using :func:`.create_engine`:: engine = create_engine( "postgresql+pg8000://scott:tiger@localhost/test", isolation_level="READ UNCOMMITTED" ) -When using the psycopg2 dialect, a psycopg2-specific method of setting -transaction isolation level is used, but the API of ``isolation_level`` -remains the same. The psycopg2 dialect also includes support -for ``AUTOCOMMIT`` isolation - see :ref:`psycopg2_isolation`. +To set using per-connection execution options:: + + connection = engine.connect() + connection = connection.execution_options(isolation_level="READ COMMITTED") + +Valid values for ``isolation_level`` include: + +* ``READ COMMITTED`` +* ``READ UNCOMMITTED`` +* ``REPEATABLE READ`` +* ``SERIALIZABLE`` + +The :mod:`~sqlalchemy.dialects.postgresql.psycopg2` dialect also offers the special level ``AUTOCOMMIT``. See +:ref:`psycopg2_isolation_level` for details. Remote / Cross-Schema Table Introspection diff --git a/lib/sqlalchemy/dialects/postgresql/psycopg2.py b/lib/sqlalchemy/dialects/postgresql/psycopg2.py index 188fb3c11a..93d834fee1 100644 --- a/lib/sqlalchemy/dialects/postgresql/psycopg2.py +++ b/lib/sqlalchemy/dialects/postgresql/psycopg2.py @@ -17,7 +17,7 @@ psycopg2 Connect Arguments psycopg2-specific keyword arguments which are accepted by :func:`.create_engine()` are: -* *server_side_cursors* - Enable the usage of "server side cursors" for SQL +* ``server_side_cursors``: Enable the usage of "server side cursors" for SQL statements which support this feature. What this essentially means from a psycopg2 point of view is that the cursor is created using a name, e.g. ``connection.cursor('some name')``, which has the effect that result rows are @@ -28,8 +28,12 @@ psycopg2-specific keyword arguments which are accepted by time are fetched over the wire to reduce conversational overhead. Note that the ``stream_results=True`` execution option is a more targeted way of enabling this mode on a per-execution basis. -* *use_native_unicode* - Enable the usage of Psycopg2 "native unicode" mode - per connection. True by default. +* ``use_native_unicode``: Enable the usage of Psycopg2 "native unicode" mode + per connection. True by default. +* ``isolation_level``: This option, available for all Posgtresql dialects, + includes the ``AUTOCOMMIT`` isolation level when using the psycopg2 + dialect. See :ref:`psycopg2_isolation_level`. + Unix Domain Connections ------------------------ @@ -60,13 +64,11 @@ The following DBAPI-specific options are respected when used with * isolation_level - Set the transaction isolation level for the lifespan of a :class:`.Connection` (can only be set on a connection, not a statement - or query). This includes the options ``SERIALIZABLE``, ``READ COMMITTED``, - ``READ UNCOMMITTED``, ``REPEATABLE READ``, and ``AUTOCOMMIT``. - - .. versionadded:: 0.8.2 support for AUTOCOMMIT isolation level when using - psycopg2. + or query). See :ref:`psycopg2_isolation_level`. -* stream_results - Enable or disable usage of server side cursors. +* stream_results - Enable or disable usage of psycopg2 server side cursors - + this feature makes use of "named" cursors in combination with special + result handling methods so that result rows are not fully buffered. If ``None`` or not set, the ``server_side_cursors`` option of the :class:`.Engine` is used. @@ -117,16 +119,31 @@ Transactions The psycopg2 dialect fully supports SAVEPOINT and two-phase commit operations. -.. _psycopg2_isolation: +.. _psycopg2_isolation_level: -Transaction Isolation Level ---------------------------- +Psycopg2 Transaction Isolation Level +------------------------------------- -The ``isolation_level`` parameter of :func:`.create_engine` here makes use +As discussed in :ref:`postgresql_isolation_level`, +all Postgresql dialects support setting of transaction isolation level +both via the ``isolation_level`` parameter passed to :func:`.create_engine`, +as well as the ``isolation_level`` argument used by :meth:`.Connection.execution_options`. +When using the psycopg2 dialect, these options make use of psycopg2's ``set_isolation_level()`` connection method, rather than -issuing a ``SET SESSION CHARACTERISTICS`` command. This because psycopg2 -resets the isolation level on each new transaction, and needs to know -at the API level what level should be used. +emitting a Postgresql directive; this is because psycopg2's API-level +setting is always emitted at the start of each transaction in any case. + +The psycopg2 dialect supports these constants for isolation level: + +* ``READ COMMITTED`` +* ``READ UNCOMMITTED`` +* ``REPEATABLE READ`` +* ``SERIALIZABLE`` +* ``AUTOCOMMIT`` + +.. versionadded:: 0.8.2 support for AUTOCOMMIT isolation level when using + psycopg2. + NOTICE logging ---------------