This is the second time I've answered this exact same problem in two

days.  It seems to be a FAQ, and I think I know why. When creating a 'c'
language function, CREATE FUNCTION is fed the shared object filename,
and seems to succeed. Only when trying to use the function is an error
thrown, by which time the coder thinks something's wrong with executing
the code, not with loading it.

I think I once saw it proposed to load shared objects at function creation
time, but that idea was shot down on the grounds of resident memory bloat,
ISTR. Here's a patch for a compromise: all it does is stat() the file,
just like the loader code does, so that the errors caused by non existent
files, and no directory 'x' permissions (the most common ones, it seems),
get caught while the developer is still thinking about code loading. It
doesn't catch all errors (like the code not being readable by the postgres
user) but seems to catch the most common, without actually opening the file.

What do you think?

Ross

src/backend/commands/define.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/define.c,v 1.41 2000/04/13 11:51:07 wieck Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/define.c,v 1.42 2000/05/12 18:51:59 momjian Exp $
  *
  * DESCRIPTION
  *	  The "DefineFoo" routines take the parse tree and pick out the
@@ -35,6 +35,8 @@
  */
 #include <ctype.h>
 #include <math.h>
+#include <sys/stat.h>
+
 
 #include "postgres.h"
 
@@ -180,6 +182,8 @@ static void
 interpret_AS_clause(const char *languageName, const List *as,
 					char **prosrc_str_p, char **probin_str_p)
 {
+	struct stat stat_buf;
+
 	Assert(as != NIL);
 
 	if (strcmp(languageName, "C") == 0)
@@ -187,9 +191,15 @@ interpret_AS_clause(const char *languageName, const List *as,
 
 		/*
 		 * For "C" language, store the file name in probin and, when
-		 * given, the link symbol name in prosrc.
+		 * given, the link symbol name in prosrc. But first, stat the
+		 * file to make sure it's there!
 		 */
+		
+		if (stat(strVal(lfirst(as)), &stat_buf) == -1)
+				elog(ERROR, "stat failed on file '%s': %m", strVal(lfirst(as)));
+
 		*probin_str_p = strVal(lfirst(as));
+
 		if (lnext(as) == NULL)
 			*prosrc_str_p = "-";
 		else