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Add pgmagic header block to store compile-time constants:

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It now only checks four things:

Major version number (7.4 or 8.1 for example)
NAMEDATALEN
FUNC_MAX_ARGS
INDEX_MAX_KEYS

The three constants were chosen because:

1. We document them in the config page in the docs
2. We mark them as changable in pg_config_manual.h
3. Changing any of these will break some of the more popular modules:

FUNC_MAX_ARGS changes fmgr interface, every module uses this NAMEDATALEN
changes syscache interface, every PL as well as tsearch uses this
INDEX_MAX_KEYS breaks tsearch and anything using GiST.

Martijn van Oosterhout
This commit is contained in:
Bruce Momjian
2006-05-30 14:09:32 +00:00
parent 87bd07d979
commit 01b2168c90
4 changed files with 149 additions and 5 deletions
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29
doc/src/sgml/xfunc.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.112 2006/04/23 03:39:52 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.113 2006/05/30 14:09:32 momjian Exp $ -->
<sect1 id="xfunc">
<title>User-Defined Functions</title>
@ -1148,6 +1148,13 @@ CREATE FUNCTION square_root(double precision) RETURNS double precision
that fails as well, the load will fail.
</para>
<para>
After the module has been found, PostgreSQL looks for its magic block.
This block contains information about the environment a module was
compiled in. The server uses this to verify the module was compiled
under the same assumptions and environment as the backend.
</para>
<para>
The user ID the <productname>PostgreSQL</productname> server runs
as must be able to traverse the path to the file you intend to
@ -1951,6 +1958,26 @@ concat_text(PG_FUNCTION_ARGS)
</para>
</listitem>
<listitem>
<para>
To ensure your module is not loaded into an incompatible backend, it
is recommended to include a magic block. To do this you must include
the header <filename>pgmagic.h</filename> and declare the block as
follows:
</para>
<programlisting>
#include "pgmagic.h"
PG_MODULE_MAGIC;
</programlisting>
<para>
If the module consists of multiple source files, this only needs to
be done in one of them.
</para>
</listitem>
<listitem>
<para>
Symbol names defined within object files must not conflict