sqlalchemy.dialects.postgresql.psycopg2

.. dialect:: postgresql+psycopg2 :name: psycopg2 :dbapi: psycopg2 :connectstring: postgresql+psycopg2://user:password@host:port/dbname[?key=value&key=value...] :url: https://pypi.org/project/psycopg2/ .. _psycopg2_toplevel: psycopg2 Connect Arguments -------------------------- Keyword arguments that are specific to the SQLAlchemy psycopg2 dialect may be passed to :func:`_sa.create_engine()`, and include the following: * ``isolation_level``: This option, available for all PostgreSQL dialects, includes the ``AUTOCOMMIT`` isolation level when using the psycopg2 dialect. This option sets the **default** isolation level for the connection that is set immediately upon connection to the database before the connection is pooled. This option is generally superseded by the more modern :paramref:`_engine.Connection.execution_options.isolation_level` execution option, detailed at :ref:`dbapi_autocommit`. .. seealso:: :ref:`psycopg2_isolation_level` :ref:`dbapi_autocommit` * ``client_encoding``: sets the client encoding in a libpq-agnostic way, using psycopg2's ``set_client_encoding()`` method. .. seealso:: :ref:`psycopg2_unicode` * ``executemany_mode``, ``executemany_batch_page_size``, ``executemany_values_page_size``: Allows use of psycopg2 extensions for optimizing "executemany"-style queries. See the referenced section below for details. .. seealso:: :ref:`psycopg2_executemany_mode` .. tip:: The above keyword arguments are **dialect** keyword arguments, meaning that they are passed as explicit keyword arguments to :func:`_sa.create_engine()`:: engine = create_engine( "postgresql+psycopg2://scott:tiger@localhost/test", isolation_level="SERIALIZABLE", ) These should not be confused with **DBAPI** connect arguments, which are passed as part of the :paramref:`_sa.create_engine.connect_args` dictionary and/or are passed in the URL query string, as detailed in the section :ref:`custom_dbapi_args`. .. _psycopg2_ssl: SSL Connections --------------- The psycopg2 module has a connection argument named ``sslmode`` for controlling its behavior regarding secure (SSL) connections. The default is ``sslmode=prefer``; it will attempt an SSL connection and if that fails it will fall back to an unencrypted connection. ``sslmode=require`` may be used to ensure that only secure connections are established. Consult the psycopg2 / libpq documentation for further options that are available. Note that ``sslmode`` is specific to psycopg2 so it is included in the connection URI:: engine = sa.create_engine( "postgresql+psycopg2://scott:tiger@192.168.0.199:5432/test?sslmode=require" ) Unix Domain Connections ------------------------ psycopg2 supports connecting via Unix domain connections. When the ``host`` portion of the URL is omitted, SQLAlchemy passes ``None`` to psycopg2, which specifies Unix-domain communication rather than TCP/IP communication:: create_engine("postgresql+psycopg2://user:password@/dbname") By default, the socket file used is to connect to a Unix-domain socket in ``/tmp``, or whatever socket directory was specified when PostgreSQL was built. This value can be overridden by passing a pathname to psycopg2, using ``host`` as an additional keyword argument:: create_engine("postgresql+psycopg2://user:password@/dbname?host=/var/lib/postgresql") .. seealso:: `PQconnectdbParams \ <https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-PQCONNECTDBPARAMS>`_ .. _psycopg2_multi_host: Specifying multiple fallback hosts ----------------------------------- psycopg2 supports multiple connection points in the connection string. When the ``host`` parameter is used multiple times in the query section of the URL, SQLAlchemy will create a single string of the host and port information provided to make the connections. Tokens may consist of ``host::port`` or just ``host``; in the latter case, the default port is selected by libpq. In the example below, three host connections are specified, for ``HostA::PortA``, ``HostB`` connecting to the default port, and ``HostC::PortC``:: create_engine( "postgresql+psycopg2://user:password@/dbname?host=HostA:PortA&host=HostB&host=HostC:PortC" ) As an alternative, libpq query string format also may be used; this specifies ``host`` and ``port`` as single query string arguments with comma-separated lists - the default port can be chosen by indicating an empty value in the comma separated list:: create_engine( "postgresql+psycopg2://user:password@/dbname?host=HostA,HostB,HostC&port=PortA,,PortC" ) With either URL style, connections to each host is attempted based on a configurable strategy, which may be configured using the libpq ``target_session_attrs`` parameter. Per libpq this defaults to ``any`` which indicates a connection to each host is then attempted until a connection is successful. Other strategies include ``primary``, ``prefer-standby``, etc. The complete list is documented by PostgreSQL at `libpq connection strings <https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING>`_. For example, to indicate two hosts using the ``primary`` strategy:: create_engine( "postgresql+psycopg2://user:password@/dbname?host=HostA:PortA&host=HostB&host=HostC:PortC&target_session_attrs=primary" ) .. versionchanged:: 1.4.40 Port specification in psycopg2 multiple host format is repaired, previously ports were not correctly interpreted in this context. libpq comma-separated format is also now supported. .. versionadded:: 1.3.20 Support for multiple hosts in PostgreSQL connection string. .. seealso:: `libpq connection strings <https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING>`_ - please refer to this section in the libpq documentation for complete background on multiple host support. Empty DSN Connections / Environment Variable Connections --------------------------------------------------------- The psycopg2 DBAPI can connect to PostgreSQL by passing an empty DSN to the libpq client library, which by default indicates to connect to a localhost PostgreSQL database that is open for "trust" connections. This behavior can be further tailored using a particular set of environment variables which are prefixed with ``PG_...``, which are consumed by ``libpq`` to take the place of any or all elements of the connection string. For this form, the URL can be passed without any elements other than the initial scheme:: engine = create_engine('postgresql+psycopg2://') In the above form, a blank "dsn" string is passed to the ``psycopg2.connect()`` function which in turn represents an empty DSN passed to libpq. .. versionadded:: 1.3.2 support for parameter-less connections with psycopg2. .. seealso:: `Environment Variables\ <https://www.postgresql.org/docs/current/libpq-envars.html>`_ - PostgreSQL documentation on how to use ``PG_...`` environment variables for connections. .. _psycopg2_execution_options: Per-Statement/Connection Execution Options ------------------------------------------- The following DBAPI-specific options are respected when used with :meth:`_engine.Connection.execution_options`, :meth:`.Executable.execution_options`, :meth:`_query.Query.execution_options`, in addition to those not specific to DBAPIs: * ``isolation_level`` - Set the transaction isolation level for the lifespan of a :class:`_engine.Connection` (can only be set on a connection, not a statement or query). See :ref:`psycopg2_isolation_level`. * ``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. Defaults to False, meaning cursors are buffered by default. * ``max_row_buffer`` - when using ``stream_results``, an integer value that specifies the maximum number of rows to buffer at a time. This is interpreted by the :class:`.BufferedRowCursorResult`, and if omitted the buffer will grow to ultimately store 1000 rows at a time. .. versionchanged:: 1.4 The ``max_row_buffer`` size can now be greater than 1000, and the buffer will grow to that size. .. _psycopg2_batch_mode: .. _psycopg2_executemany_mode: Psycopg2 Fast Execution Helpers ------------------------------- Modern versions of psycopg2 include a feature known as `Fast Execution Helpers \ <https://initd.org/psycopg/docs/extras.html#fast-execution-helpers>`_, which have been shown in benchmarking to improve psycopg2's executemany() performance, primarily with INSERT statements, by at least an order of magnitude. SQLAlchemy implements a native form of the "insert many values" handler that will rewrite a single-row INSERT statement to accommodate for many values at once within an extended VALUES clause; this handler is equivalent to psycopg2's ``execute_values()`` handler; an overview of this feature and its configuration are at :ref:`engine_insertmanyvalues`. .. versionadded:: 2.0 Replaced psycopg2's ``execute_values()`` fast execution helper with a native SQLAlchemy mechanism referred towards as :ref:`insertmanyvalues <engine_insertmanyvalues>`. The psycopg2 dialect retains the ability to use the psycopg2-specific ``execute_batch()`` feature, although it is not expected that this is a widely used feature. The use of this extension may be enabled using the ``executemany_mode`` flag which may be passed to :func:`_sa.create_engine`:: engine = create_engine( "postgresql+psycopg2://scott:tiger@host/dbname", executemany_mode='values_plus_batch') Possible options for ``executemany_mode`` include: * ``values_only`` - this is the default value. SQLAlchemy's native :ref:`insertmanyvalues <engine_insertmanyvalues>` handler is used for qualifying INSERT statements, assuming :paramref:`_sa.create_engine.use_insertmanyvalues` is left at its default value of ``True``. This handler rewrites simple INSERT statements to include multiple VALUES clauses so that many parameter sets can be inserted with one statement. * ``'values_plus_batch'``- SQLAlchemy's native :ref:`insertmanyvalues <engine_insertmanyvalues>` handler is used for qualifying INSERT statements, assuming :paramref:`_sa.create_engine.use_insertmanyvalues` is left at its default value of ``True``. Then, psycopg2's ``execute_batch()`` handler is used for qualifying UPDATE and DELETE statements when executed with multiple parameter sets. When using this mode, the :attr:`_engine.CursorResult.rowcount` attribute will not contain a value for executemany-style executions against UPDATE and DELETE statements. .. versionchanged:: 2.0 Removed the ``'batch'`` and ``'None'`` options from psycopg2 ``executemany_mode``. Control over batching for INSERT statements is now configured via the :paramref:`_sa.create_engine.use_insertmanyvalues` engine-level parameter. The term "qualifying statements" refers to the statement being executed being a Core :func:`_expression.insert`, :func:`_expression.update` or :func:`_expression.delete` construct, and **not** a plain textual SQL string or one constructed using :func:`_expression.text`. It also may **not** be a special "extension" statement such as an "ON CONFLICT" "upsert" statement. When using the ORM, all insert/update/delete statements used by the ORM flush process are qualifying. The "page size" for the psycopg2 "batch" strategy can be affected by using the ``executemany_batch_page_size`` parameter, which defaults to 100. For the "insertmanyvalues" feature, the page size can be controlled using the :paramref:`_sa.create_engine.insertmanyvalues_page_size` parameter, which defaults to 1000. An example of modifying both parameters is below:: engine = create_engine( "postgresql+psycopg2://scott:tiger@host/dbname", executemany_mode='values_plus_batch', insertmanyvalues_page_size=5000, executemany_batch_page_size=500) .. seealso:: :ref:`engine_insertmanyvalues` - background on "insertmanyvalues" :ref:`tutorial_multiple_parameters` - General information on using the :class:`_engine.Connection` object to execute statements in such a way as to make use of the DBAPI ``.executemany()`` method. .. _psycopg2_unicode: Unicode with Psycopg2 ---------------------- The psycopg2 DBAPI driver supports Unicode data transparently. The client character encoding can be controlled for the psycopg2 dialect in the following ways: * For PostgreSQL 9.1 and above, the ``client_encoding`` parameter may be passed in the database URL; this parameter is consumed by the underlying ``libpq`` PostgreSQL client library:: engine = create_engine("postgresql+psycopg2://user:pass@host/dbname?client_encoding=utf8") Alternatively, the above ``client_encoding`` value may be passed using :paramref:`_sa.create_engine.connect_args` for programmatic establishment with ``libpq``:: engine = create_engine( "postgresql+psycopg2://user:pass@host/dbname", connect_args={'client_encoding': 'utf8'} ) * For all PostgreSQL versions, psycopg2 supports a client-side encoding value that will be passed to database connections when they are first established. The SQLAlchemy psycopg2 dialect supports this using the ``client_encoding`` parameter passed to :func:`_sa.create_engine`:: engine = create_engine( "postgresql+psycopg2://user:pass@host/dbname", client_encoding="utf8" ) .. tip:: The above ``client_encoding`` parameter admittedly is very similar in appearance to usage of the parameter within the :paramref:`_sa.create_engine.connect_args` dictionary; the difference above is that the parameter is consumed by psycopg2 and is passed to the database connection using ``SET client_encoding TO 'utf8'``; in the previously mentioned style, the parameter is instead passed through psycopg2 and consumed by the ``libpq`` library. * A common way to set up client encoding with PostgreSQL databases is to ensure it is configured within the server-side postgresql.conf file; this is the recommended way to set encoding for a server that is consistently of one encoding in all databases:: # postgresql.conf file # client_encoding = sql_ascii # actually, defaults to database # encoding client_encoding = utf8 Transactions ------------ The psycopg2 dialect fully supports SAVEPOINT and two-phase commit operations. .. _psycopg2_isolation_level: Psycopg2 Transaction Isolation Level ------------------------------------- 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:`_sa.create_engine` , as well as the ``isolation_level`` argument used by :meth:`_engine.Connection.execution_options`. When using the psycopg2 dialect , these options make use of psycopg2's ``set_isolation_level()`` connection method, rather than 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`` .. seealso:: :ref:`postgresql_isolation_level` :ref:`pg8000_isolation_level` NOTICE logging --------------- The psycopg2 dialect will log PostgreSQL NOTICE messages via the ``sqlalchemy.dialects.postgresql`` logger. When this logger is set to the ``logging.INFO`` level, notice messages will be logged:: import logging logging.getLogger('sqlalchemy.dialects.postgresql').setLevel(logging.INFO) Above, it is assumed that logging is configured externally. If this is not the case, configuration such as ``logging.basicConfig()`` must be utilized:: import logging logging.basicConfig() # log messages to stdout logging.getLogger('sqlalchemy.dialects.postgresql').setLevel(logging.INFO) .. seealso:: `Logging HOWTO <https://docs.python.org/3/howto/logging.html>`_ - on the python.org website .. _psycopg2_hstore: HSTORE type ------------ The ``psycopg2`` DBAPI includes an extension to natively handle marshalling of the HSTORE type. The SQLAlchemy psycopg2 dialect will enable this extension by default when psycopg2 version 2.4 or greater is used, and it is detected that the target database has the HSTORE type set up for use. In other words, when the dialect makes the first connection, a sequence like the following is performed: 1. Request the available HSTORE oids using ``psycopg2.extras.HstoreAdapter.get_oids()``. If this function returns a list of HSTORE identifiers, we then determine that the ``HSTORE`` extension is present. This function is **skipped** if the version of psycopg2 installed is less than version 2.4. 2. If the ``use_native_hstore`` flag is at its default of ``True``, and we've detected that ``HSTORE`` oids are available, the ``psycopg2.extensions.register_hstore()`` extension is invoked for all connections. The ``register_hstore()`` extension has the effect of **all Python dictionaries being accepted as parameters regardless of the type of target column in SQL**. The dictionaries are converted by this extension into a textual HSTORE expression. If this behavior is not desired, disable the use of the hstore extension by setting ``use_native_hstore`` to ``False`` as follows:: engine = create_engine("postgresql+psycopg2://scott:tiger@localhost/test", use_native_hstore=False) The ``HSTORE`` type is **still supported** when the ``psycopg2.extensions.register_hstore()`` extension is not used. It merely means that the coercion between Python dictionaries and the HSTORE string format, on both the parameter side and the result side, will take place within SQLAlchemy's own marshalling logic, and not that of ``psycopg2`` which may be more performant.