libpq-dev

Overview

The libpq-dev library is built following Debian's libpq-dev package idea: it contains a minimal set of PostgreSQL binaries and headers required for building 3rd-party applications for PostgreSQL_.

Moreover this package provides even smaller subset of binaries than Debian's libpq-dev package and was designed this way on purpose. The main goal is to provide all requirements for building Psycopg2.

This package is meant to be built as platform-specific binary Python wheels, contains only PostgreSQL binaries and 0 Python code.

Rationale

The Psycopg2 library is built as a wrapper around libpq and mostly written in C. It is distributed as an sdist and being built during installation. For this reason it requires some PostgreSQL binaries and headers to be present during installation.

For simple environments where database server and application server combine the same host it is not an issue but it might be a different case for distributed systems. This leads to the need to install some of PostgreSQL_ binaries on the application server as well.

On top of that there might be a situation when single application server needs to host several applications that use different versions of PostgreSQL and thus Psycopg2 needs to be built against different versions_ of libpq.

Contents

The package contains:

- **pg_config**
- **libpq.a** (static build of ``libpq``)
- a number of additional headers

For full list of files please take a look into setup.cfg/[files]/data_files.

Once more, 0 Python sources or any other stuff.

Usage

The usage is pretty simple and straight forward: install libpq-dev of required version (the same version as your PostgreSQL version) before installing Psycopg2_.

::

$ pip install libpq-dev==9.4.3

$ pip install psycopg2

Please note that Psycopg2 prefers static linking against libpq so if you distributing your application and all its dependencies with wheels or something like Platter then you don't need need to ship libpq-dev as long as you have Psycopg2_ wheel built with it.

Limitation and Known Issues

Currently libpq-dev is being built only for Linux with Python 2.7, 3.3, 3.4 from PostgreSQL 9.* sources.

If there will be demand for other platforms, Python versions or older PostgreSQL versions new builds will be added.

Also please note that there is known issue with PIP and some Python packages (including Psycopg2) that doesn't allow you to do:

::

$ pip install libpq-dev==9.4.3 psycopg2

or put these names into requirements.txt and then run pip install -r requirements.txt. This is because Psycopg2_ requires pg_config and other PostgreSQL binaries to be present in order to run egg_info command (which is executed by PIP during normal installation process).

Unfortunately there is nothing we can do about it right now but we hope that either this will be handled somehow in future PIP releases or fixed in Psycopg2_.

Further Development

We assume that there might be demand in builds for additional platforms or Python versions.

Also there may be other Python libraries that may be used with this package. In case this package is missing some binaries requried by libraries other that Pscyopg2_ they will be added.

.. _Debian's libpq-dev package: https://packages.debian.org/sid/libpq-dev .. _PostgreSQL: http://www.postgresql.org/ .. _Psycopg2: https://pypi.python.org/pypi/psycopg2 .. _platform-specific: https://packaging.python.org/en/latest/distributing.html#platform-wheels .. _Python wheels: http://pythonwheels.com/ .. _built against different versions: http://www.leeladharan.com/importerror-psycopg-so:-undefined-symbol:-lo-truncate64 .. _Platter: http://platter.pocoo.org/ .. _known issue with PIP: https://github.com/pypa/pip/issues/25