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>Chapter 35. Extending <ACRONYM
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>SQL</ACRONYM
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="EXTEND-PGXS"
>35.16. Extension Building Infrastructure</A
></H1
><P
>    If you are thinking about distributing your
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension modules, setting up a
    portable build system for them can be fairly difficult.  Therefore
    the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation provides a build
    infrastructure for extensions, called <ACRONYM
CLASS="ACRONYM"
>PGXS</ACRONYM
>, so
    that simple extension modules can be built simply against an
    already installed server.  <ACRONYM
CLASS="ACRONYM"
>PGXS</ACRONYM
> is mainly intended
    for extensions that include C code, although it can be used for
    pure-SQL extensions too.  Note that <ACRONYM
CLASS="ACRONYM"
>PGXS</ACRONYM
> is not
    intended to be a universal build system framework that can be used
    to build any software interfacing to <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>;
    it simply automates common build rules for simple server extension
    modules.  For more complicated packages, you might need to write your
    own build system.
   </P
><P
>    To use the <ACRONYM
CLASS="ACRONYM"
>PGXS</ACRONYM
> infrastructure for your extension,
    you must write a simple makefile.
    In the makefile, you need to set some variables
    and finally include the global <ACRONYM
CLASS="ACRONYM"
>PGXS</ACRONYM
> makefile.
    Here is an example that builds an extension module named
    <TT
CLASS="LITERAL"
>isbn_issn</TT
>, consisting of a shared library containing
    some C code, an extension control file, a SQL script, and a documentation
    text file:
</P><PRE
CLASS="PROGRAMLISTING"
>MODULES = isbn_issn
EXTENSION = isbn_issn
DATA = isbn_issn--1.0.sql
DOCS = README.isbn_issn

PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)</PRE
><P>
    The last three lines should always be the same.  Earlier in the
    file, you assign variables or add custom
    <SPAN
CLASS="APPLICATION"
>make</SPAN
> rules.
   </P
><P
>    Set one of these three variables to specify what is built:

    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="VARNAME"
>MODULES</TT
></DT
><DD
><P
>        list of shared-library objects to be built from source files with same
        stem (do not include library suffixes in this list)
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>MODULE_big</TT
></DT
><DD
><P
>        a shared library to build from multiple source files
        (list object files in <TT
CLASS="VARNAME"
>OBJS</TT
>)
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>PROGRAM</TT
></DT
><DD
><P
>        an executable program to build
        (list object files in <TT
CLASS="VARNAME"
>OBJS</TT
>)
       </P
></DD
></DL
></DIV
><P>

    The following variables can also be set:

    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="VARNAME"
>EXTENSION</TT
></DT
><DD
><P
>        extension name(s); for each name you must provide an
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>extension</I
></TT
>.control</TT
> file,
        which will be installed into
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/share/extension</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>MODULEDIR</TT
></DT
><DD
><P
>        subdirectory of <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/share</TT
>
        into which DATA and DOCS files should be installed
        (if not set, default is <TT
CLASS="LITERAL"
>extension</TT
> if
        <TT
CLASS="VARNAME"
>EXTENSION</TT
> is set,
        or <TT
CLASS="LITERAL"
>contrib</TT
> if not)
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>DATA</TT
></DT
><DD
><P
>        random files to install into <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/share/$MODULEDIR</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>DATA_built</TT
></DT
><DD
><P
>        random files to install into
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/share/$MODULEDIR</TT
>,
        which need to be built first
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>DATA_TSEARCH</TT
></DT
><DD
><P
>        random files to install under
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/share/tsearch_data</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>DOCS</TT
></DT
><DD
><P
>        random files to install under
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/doc/$MODULEDIR</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>SCRIPTS</TT
></DT
><DD
><P
>        script files (not binaries) to install into
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/bin</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>SCRIPTS_built</TT
></DT
><DD
><P
>        script files (not binaries) to install into
        <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>prefix</I
></TT
>/bin</TT
>,
        which need to be built first
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>REGRESS</TT
></DT
><DD
><P
>        list of regression test cases (without suffix), see below
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>REGRESS_OPTS</TT
></DT
><DD
><P
>        additional switches to pass to <SPAN
CLASS="APPLICATION"
>pg_regress</SPAN
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>EXTRA_CLEAN</TT
></DT
><DD
><P
>        extra files to remove in <TT
CLASS="LITERAL"
>make clean</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>PG_CPPFLAGS</TT
></DT
><DD
><P
>        will be added to <TT
CLASS="VARNAME"
>CPPFLAGS</TT
>
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>PG_LIBS</TT
></DT
><DD
><P
>        will be added to <TT
CLASS="VARNAME"
>PROGRAM</TT
> link line
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>SHLIB_LINK</TT
></DT
><DD
><P
>        will be added to <TT
CLASS="VARNAME"
>MODULE_big</TT
> link line
       </P
></DD
><DT
><TT
CLASS="VARNAME"
>PG_CONFIG</TT
></DT
><DD
><P
>        path to <SPAN
CLASS="APPLICATION"
>pg_config</SPAN
> program for the
        <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation to build against
        (typically just <TT
CLASS="LITERAL"
>pg_config</TT
> to use the first one in your
        <TT
CLASS="VARNAME"
>PATH</TT
>)
       </P
></DD
></DL
></DIV
><P>
   </P
><P
>    Put this makefile as <TT
CLASS="LITERAL"
>Makefile</TT
> in the directory
    which holds your extension. Then you can do
    <TT
CLASS="LITERAL"
>make</TT
> to compile, and then <TT
CLASS="LITERAL"
>make
    install</TT
> to install your module.  By default, the extension is
    compiled and installed for the
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> installation that
    corresponds to the first <TT
CLASS="COMMAND"
>pg_config</TT
> program
    found in your <TT
CLASS="VARNAME"
>PATH</TT
>.  You can use a different installation by
    setting <TT
CLASS="VARNAME"
>PG_CONFIG</TT
> to point to its
    <TT
CLASS="COMMAND"
>pg_config</TT
> program, either within the makefile
    or on the <TT
CLASS="LITERAL"
>make</TT
> command line.
   </P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>     Changing <TT
CLASS="VARNAME"
>PG_CONFIG</TT
> only works when building
     against <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.3 or later.
     With older releases it does not work to set it to anything except
     <TT
CLASS="LITERAL"
>pg_config</TT
>; you must alter your <TT
CLASS="VARNAME"
>PATH</TT
>
     to select the installation to build against.
    </P
></TD
></TR
></TABLE
></DIV
><P
>    The scripts listed in the <TT
CLASS="VARNAME"
>REGRESS</TT
> variable are used for
    regression testing of your module, which can be invoked by <TT
CLASS="LITERAL"
>make
    installcheck</TT
> after doing <TT
CLASS="LITERAL"
>make install</TT
>.  For this to
    work you must have a running <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server.
    The script files listed in <TT
CLASS="VARNAME"
>REGRESS</TT
> must appear in a
    subdirectory named <TT
CLASS="LITERAL"
>sql/</TT
> in your extension's directory.
    These files must have extension <TT
CLASS="LITERAL"
>.sql</TT
>, which must not be
    included in the <TT
CLASS="VARNAME"
>REGRESS</TT
> list in the makefile.  For each
    test there should also be a file containing the expected output in a
    subdirectory named <TT
CLASS="LITERAL"
>expected/</TT
>, with the same stem and
    extension <TT
CLASS="LITERAL"
>.out</TT
>.  <TT
CLASS="LITERAL"
>make installcheck</TT
>
    executes each test script with <SPAN
CLASS="APPLICATION"
>psql</SPAN
>, and compares the
    resulting output to the matching expected file.  Any differences will be
    written to the file <TT
CLASS="LITERAL"
>regression.diffs</TT
> in <TT
CLASS="COMMAND"
>diff
    -c</TT
> format.  Note that trying to run a test that is missing its
    expected file will be reported as <SPAN
CLASS="QUOTE"
>"trouble"</SPAN
>, so make sure you
    have all expected files.
   </P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>     The easiest way to create the expected files is to create empty files,
     then do a test run (which will of course report differences).  Inspect
     the actual result files found in the <TT
CLASS="LITERAL"
>results/</TT
>
     directory, then copy them to <TT
CLASS="LITERAL"
>expected/</TT
> if they match
     what you expect from the test.
    </P
></BLOCKQUOTE
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