How to reload a postgres C extension?-CodePudding

I've created a C extension defining the shell of a function that I can call from SQL code in Postgresql 12.3. I'm using PGXS to build and install the extension. I can build, install and call the function, but if I make changes and reinstall, the changes don't show.

The make file is:

MODULES = bar
EXTENSION = bar
DATA = bar--0.0.1.sql
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)

bar.control is

comment = 'Simple bar function'
default_version = '0.0.1'
relocatable = true
module_pathname = '$libdir/bar'

bar--0.0.1.sql is:

CREATE OR REPLACE FUNCTION
bar(jsonb) RETURNS int AS 'MODULE_PATHNAME','bar'
LANGUAGE C STRICT;

bar.c is:

#include "postgres.h"
#include "fmgr.h"

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(bar);

Datum bar(PG_FUNCTION_ARGS)
{
    PG_RETURN_INT32(101);
}

I run make install to do the install. And then drop extension bar; create extension bar; but the changes won't show when I call the function. The only way I can install a new version is to restart postgres. What step am I missing?

CodePudding user response：

Well, I discovered that if I just create a new connection to the DB the changes will show. That isn't so bad, I suppose. Does that have to do with how postgres uses fork() to create a new process for each connection?

CodePudding user response：

When you execute your function, the shared library gets loaded into your backend process and stays there. Replacing the shared library on disk does not modify the in-memory copy loaded into your process. You have to start a new database connection and execute the function again to get the new version.