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Add PL/Sample to src/test/modules/

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PL/Sample is an example template of procedural-language handler.  This
can be used as a base to implement a custom PL, or as a facility to test
APIs dedicated to PLs.  Much more could be done in this module, like
adding a simple validator, but this is left as future work.

The documentation included originally some C code to understand the
basics of PL handler implementation, but it was outdated, and not really
helpful either if trying to implement a new procedural language,
particularly when it came to the integration of a PL installation with
CREATE EXTENSION.

Author: Mark Wong
Reviewed-by: Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/20200612172648.GA3327@2ndQuadrant.com
This commit is contained in:
Michael Paquier
2020-08-18 11:10:50 +09:00
parent 6e70443eda
commit adbe62d04b
10 changed files with 290 additions and 56 deletions
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60
doc/src/sgml/plhandler.sgml
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@ -96,62 +96,10 @@
</para>
<para>
This is a template for a procedural-language handler written in C:
<programlisting>
#include "postgres.h"
#include "executor/spi.h"
#include "commands/trigger.h"
#include "fmgr.h"
#include "access/heapam.h"
#include "utils/syscache.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(plsample_call_handler);
Datum
plsample_call_handler(PG_FUNCTION_ARGS)
{
Datum retval;
if (CALLED_AS_TRIGGER(fcinfo))
{
/*
* Called as a trigger function
*/
TriggerData *trigdata = (TriggerData *) fcinfo-&gt;context;
retval = ...
}
else
{
/*
* Called as a function
*/
retval = ...
}
return retval;
}
</programlisting>
Only a few thousand lines of code have to be added instead of the
dots to complete the call handler.
</para>
<para>
After having compiled the handler function into a loadable module
(see <xref linkend="dfunc"/>), the following commands then
register the sample procedural language:
<programlisting>
CREATE FUNCTION plsample_call_handler() RETURNS language_handler
AS '<replaceable>filename</replaceable>'
LANGUAGE C;
CREATE LANGUAGE plsample
HANDLER plsample_call_handler;
</programlisting>
A template for a procedural-language handler written as a C extension is
provided in <literal>src/test/modules/plsample</literal>. This is a
working sample demonstrating one way to create a procedural-language
handler, process parameters, and return a value.
</para>
<para>