void
_PG_fini(void)
{                            /* Uninstall hooks. */                        shmem_startup_hook = prev_shmem_startup_hook;                        ExecutorStart_hook = prev_ExecutorStart;                        ExecutorRun_hook = prev_ExecutorRun;                        ExecutorFinish_hook = prev_ExecutorFinish;                        ExecutorEnd_hook = prev_ExecutorEnd;                        ProcessUtility_hook = prev_ProcessUtility;
}                            

[root@server contrib]# pwd
/soft/postgresql-9.1.2/contrib
[root@server contrib]# mkdir dbrestrict
[root@server contrib]# cd dbrestrict

[root@server dbrestrict]# pwd
/soft/postgresql-9.1.2/contrib/dbrestrict
[root@server dbrestrict]# cat dbrestrict.c
/** dbrestrict.c* Restrict drop of a given database to a given super-superuser only.* Michael Paquier, 2013* Under license "do whatever you want with that"*/
#include "postgres.h"
#include "miscadmin.h"
#include "tcop/utility.h"PG_MODULE_MAGIC;void _PG_init(void);
void _PG_fini(void);static char *undroppabledb = "foodb";
static char *supersuperuser = "foo";static ProcessUtility_hook_type prev_utility_hook = NULL;static void dbrestrict_utility(Node *parsetree, const char *queryString, ParamListInfo params,bool isTopLevel, DestReceiver *dest,char *completionTag);/** Personal process for DB drop restriction*/
static
void dbrestrict_utility(Node *parsetree,const char *queryString,ParamListInfo params,bool isTopLevel,DestReceiver *dest,char *completionTag)
{/* Do our custom process on drop database */switch (nodeTag(parsetree)){case T_DropdbStmt:{DropdbStmt *stmt = (DropdbStmt *) parsetree;char *username = GetUserNameFromId(GetUserId());/** Check that only the authorized superuser foo can* drop the database undroppable_foodb.*/if (strcmp(stmt->dbname, undroppabledb) == 0 &&strcmp(username, supersuperuser) != 0)ereport(ERROR,(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),errmsg("Only super-superuser \"%s\" can drop database \"%s\"",supersuperuser, undroppabledb)));break;}default:break;}/* Fallback to normal process */standard_ProcessUtility(parsetree, queryString, params, isTopLevel,dest,completionTag);
}/** _PG_init* Install the hook.*/
void
_PG_init(void)
{prev_utility_hook = ProcessUtility_hook;ProcessUtility_hook = dbrestrict_utility;
}/** _PG_fini* Uninstall the hook.*/
void
_PG_fini(void)
{ProcessUtility_hook = prev_utility_hook;
}
[root@server dbrestrict]# 

[root@server dbrestrict]# cat Makefile
# contrib/dbrestrict/MakefileMODULES = dbrestrict
OBJS = dbrestreict.soifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/dbrestrict
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif[root@server dbrestrict]# 

[root@server dbrestrict]# make
gcc -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I. -I. -I../../src/include -D_GNU_SOURCE   -c -o dbrestrict.o dbrestrict.c
gcc -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wformat-security -fno-strict-aliasing -fwrapv -fpic -L../../src/port  -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags  -shared -o dbrestrict.so dbrestrict.o
rm dbrestrict.o
[root@server dbrestrict]# ls
Makefile  dbrestrict.c  dbrestrict.so
[root@server dbrestrict]# make install
/bin/mkdir -p '/usr/local/pgsql/lib'
/bin/sh ../../config/install-sh -c -m 755  dbrestrict.so '/usr/local/pgsql/lib/'
[root@server dbrestrict]# 

[postgres@server data]$ vim postgresql.conf

[postgres@server data]$ cat postgresql.conf | grep 'preload'
shared_preload_libraries = 'dbrestrict'         # (change requires restart)
#local_preload_libraries = ''
[postgres@server data]$ 

shared_preload_libraries = '$libdir/dbms_pipe,$libdir/edb_gen'

[postgres@server pgsql]$ ./bin/pg_ctl -D ./data start
server starting
[postgres@server pgsql]$ LOG:  loaded library "dbrestrict"
LOG:  database system was shut down at 2013-06-19 21:05:17 CST
LOG:  autovacuum launcher started
LOG:  database system is ready to accept connections

postgres=# create database foodb;
CREATE DATABASE
postgres=# create role foo;
CREATE ROLE
postgres=# \c postgres foo;
FATAL:  role "foo" is not permitted to log in
Previous connection kept
postgres=# drop role foo;
DROP ROLE
postgres=# create role foo login;
CREATE ROLE
postgres=# \c postgres foo;
You are now connected to database "postgres" as user "foo".
postgres=> drop database foodb;
ERROR:  must be owner of database foodb
postgres=> postgres=# create role goo login;
CREATE ROLE
postgres=# \c postgres goo;
You are now connected to database "postgres" as user "goo".postgres=> drop database foodb;
ERROR:  Only super-superuser "foo" can drop database "foodb"
postgres=>