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- Committer: Federico Di Gregorio
- Date: 2004-10-29 16:15:45 UTC
- Revision ID: fog-a4e5ae2c65dfd04775bcecac32ed8e8dda664017
Undo of wrong commit of 1.1.x source code over 2.x.
added
removed
README
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psycopg - Python-PostgreSQL Database Adapter
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psycopg is a PostgreSQL database adapter for the Python programming language
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(just like pygresql and popy.) It was written from scratch with the aim of
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being very small and fast, and stable as a rock. The main advantages of
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psycopg are that it supports (well... *will* support) the full Python
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DBAPI-2.0 and being thread safe at level 2.
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psycopg is different from the other database adapter because it was designed
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for heavily multi-threaded applications that create and destroy lots of
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cursors and make a conspicuous number of concurrent INSERTs or UPDATEs.
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Every open Python connection keeps a pool of real (UNIX or TCP/IP) connections
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to the database. Every time a new cursor is created, a new connection does not
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need to be opened; instead one of the unused connections from the pool is
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used. That makes psycopg very fast in typical client-server applications that
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create a servicing thread every time a client request arrives.
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psycopg now support the Python DBAPI-2.0 completely. There are confirmed
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reports of psycopg compiling and running on Linux and FreeBSD on i386, Solaris
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and MacOS X.
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Extensions to the Python DBAPI-2.0
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----------------------------------
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psycopg offers some little extensions on the Python DBAPI-2.0. Note that the
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extension do not make psycopg incompatible and you can still use it without
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ever knowing the extensions are here.
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The DBAPI-2.0 mandates that cursors derived from the same connection are not
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isolated, i.e., changes done to the database by one of them should be
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immediately visible by all the others. This is done by serializing the queries
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on the same physical connection to the database (PGconn struct in C.)
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Serializing queries when the network latencies are hight (and network speed is
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low) dramatically lowers performance, so it is possible to put a connection
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into not-serialized mode, by calling the .serialize() method giving it a
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0-value argument or by creating a connection using the following code:
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conn = psycopg.connect("dbname=...", serialize=0)
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After that every cursor will get its own physical connection to the database
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and multiple threads will go at full speed. Note that this feature makes the
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new cursors non-compliant respect to the DBAPI-2.0.
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The main extension is that we support (on not-serialized cursors) per-cursor
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commits. If you do a commit() on the connection all the changes on all the
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cursors derived from that connection are committed to the database (in random
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order, so take your care.) But you can also call commit() on a single cursor
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to commit just the operations done on that cursor. Pretty nice.
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Note that you *do have* to call .commit() on the cursors or on the connection
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if you want to change your database. Note also that you *do have* to call
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commit() on a cursor even before a SELECT if you want to see the changes
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apported by other threads to the database.
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Also note that you *can't* (I repeat: *you* *can't*) call .commit() on cursor
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derived from a serialized connection: trying that will give you an exception
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with the message: "serialized connection: cannot commit on this cursor". If
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you want to use the per-cursor commit feature you need to create a
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non-serialized connection, as explained above.
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From version 0.4.1 psycopg supports autocommit mode. You can set the default
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mode for new cursor by setting the 'autocommit' variable to 0 or 1 on the
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connection before creating a new cursor with the cursor() method. On an
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already created cursor you can change the commit mode by calling the
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autocommit() method. Giving no arguments or 1 switches autocommit on, 0
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switches it off.
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Obviously everything said about commit is valid for rollbacks too.
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The type system
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---------------
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The DBAPI-2.0 specify that should be possible to check for the column type
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reported in the second field of the description tuple of the cursor used for a
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SELECT using 'singletons' like NUMBER, STRING, etc. While this is fully
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supported by psycopg from release 0.3 on, we went forward and implemented
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support for custom typecasting from PostgreSQL to Python types using
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user-defined functions. See the examples test/check_types.py and
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doc/examples/usercast.py for more information. In particular usercast_test.py
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shows how to implement a callback that translates the PostgreSQL box type to
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an ad-hoc Python class with instances created automagically on SELECT.
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Compile-time configuration options
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----------------------------------
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To build psycopg you will need a C compiler (gcc), the Python development
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files (headers and libraries), the PostgreSQL header and libraries and the
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mxDateTime header files (and the mxDateTime Python package installed, version
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>= 2.0.0, of curse.)
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The following options are specific to psycopg and can be set when running
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configure before issuing 'make' to compile the package.
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--with-postgres-libraries=DIR
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PostgreSQL 7.x libraries (libpq.so) are in directory DIR
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--with-postgres-includes=DIR
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PostgreSQL 7.x header files are located in directory DIR
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--with-mxdatetime-includes=DIR
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MXDateTime Python extension header files are located in directory DIR
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--with-zope=DIR
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install the ZPsycopgDA Zope Product into DIR (use 'make install-zope')
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--enable-devel[=yes/no]
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Enable developer features like debugging output and extra assertions.
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Some random notes about python versions and paths:
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1/ If possible, don't use the configure arguments --with-python-prefix
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and --with-python-exec-prefix; the configure script is able to guess
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the correct values from you python installation.
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2/ If you have more than one Python version installed, use the arguments
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--with-python (giving it the *full*, *absolute* path to the Python
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interpreter) and --with-python-version (giving it the corresponding
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version, like 1.5 or 2.1.)
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Common problems while building psycopg:
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1/ if your compiler does not find some postgres headers try copying all the
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headers from the postgres _source_ distribution to a single place. Also,
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if building postgresql from source, make sure to install all headers by
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the "make install-all-headers" target.
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2/ if you have the same problem with mx.DateTime, try using the source
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directory again; the install script does not copy all the headers, same
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way as postgres install procedure does.
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3/ under MacOS X you may need to run the runlib program on the posgres
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installed libraries before trying to compile psycopg. Also, if you
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get compilation errors there is a change your python was not compiled
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correctly and psycopg is grabbing the wrong compile-time options from
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python's Makefile. try setting the OPT and LDFLAG environment variables
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to something usefull, as in the next example:
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OPT="-no-cpp-precomp" LDFLAGS="-flat-namespace" ./configure ...
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psycopg is a PostgreSQL database adapter for the Python programming
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language. This is version 2, a complete rewrite of the original code to
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provide new-style classes for connection and cursor objects and other sweet
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candies. Like the original, psycopg 2 was written with the aim of being
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very small and fast, and stable as a rock.
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psycopg is different from the other database adapter because it was
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designed for heavily multi-threaded applications that create and destroy
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lots of cursors and make a conspicuous number of concurrent INSERTs or
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UPDATEs. psycopg 2 also provide full asycronous operations for the really
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brave programmer.
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There are confirmed reports of psycopg 1.x compiling and running on Linux
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and FreeBSD on i386, Solaris, MacOS X and win32 architectures. psycopg 2
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does not introduce build-wise incompatible changes so it should be able to
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compile on all architectures just as its predecessor did.
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Now go read the INSTALL file. More information about psycopg extensions to
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the DBAPI-2.0 is available in the files located in the doc/ direcory.
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Licence
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-------
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version. See file COPYING for details.
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As a special exception, specific permission is granted for the GPLed
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code in this distribition to be linked to OpenSSL and PostgreSQL libpq
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without invoking GPL clause 2(b).
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If you prefer you can use the Zope Database Adapter ZPsycopgDA (i.e.,
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every file inside the ZPsycopgDA directory) user the ZPL license as
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published on the Zope web site, http://www.zope.org/Resources/ZPL.
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psycopg is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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As a special exception, specific permission is granted for the GPLed code in
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this distribition to be linked to OpenSSL and PostgreSQL libpq without
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invoking GPL clause 2(b).
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If you prefer you can use the Zope Database Adapter ZPsycopgDA (i.e., every
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file inside the ZPsycopgDA directory) under the ZPL license as published on
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the Zope web site, http://www.zope.org/Resources/ZPL. The ZPL is perfectly
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compatible with the GPL
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psycopg is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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details.
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