Merge the last few variable.c configuration variables into the generic

GUC support.  It's now possible to set datestyle, timezone, and
client_encoding from postgresql.conf and per-database or per-user
settings.  Also, implement rollback of SET commands that occur in a
transaction that later fails.  Create a SET LOCAL var = value syntax
that sets the variable only for the duration of the current transaction.
All per previous discussions in pghackers.

src/backend/utils/misc/README

@@ -0,0 +1,136 @@
+$Header: /cvsroot/pgsql/src/backend/utils/misc/README,v 1.1 2002/05/17 01:19:18 tgl Exp $
+
+
+GUC IMPLEMENTATION NOTES
+
+The GUC (Grand Unified Configuration) module implements configuration
+variables of multiple types (currently boolean, int, float, and string).
+Variable settings can come from various places, with a priority ordering
+determining which setting is used.
+
+
+PER-VARIABLE HOOKS
+
+Each variable known to GUC can optionally have an assign_hook and/or
+a show_hook to provide customized behavior.  Assign hooks are used to
+perform validity checking on variable values (above and beyond what
+GUC can do).  They are also used to update any derived state that needs
+to change when a GUC variable is set.  Show hooks are used to modify
+the default SHOW display for a variable.
+
+If an assign_hook is provided, it points to a function of the signature
+	bool assign_hook(newvalue, bool doit, bool interactive)
+where the type of 'newvalue' matches the kind of variable.  This function
+is called immediately before actually setting the variable's value (so it
+can look at the actual variable to determine the old value).  If the
+function returns "true" then the assignment is completed; if it returns
+"false" then newvalue is considered invalid and the assignment is not
+performed.  If "doit" is false then the function should simply check
+validity of newvalue and not change any derived state.  "interactive" is
+true when we are performing a SET command; in this case it is okay for the
+assign_hook to raise an error via elog().  If the function returns false
+for an interactive assignment then guc.c will report a generic "invalid
+value" error message.  (An internal elog() in an assign_hook is only
+needed if you want to generate a specialized error message.)  But when
+"interactive" is false we are reading a non-interactive option source,
+such as postgresql.conf.  In this case the assign_hook should *not* elog
+but should just return false if it doesn't like the newvalue.  (An
+elog(LOG) call would be acceptable if you feel a need for a custom
+complaint in this situation.)
+
+For string variables, the signature for assign hooks is a bit different:
+	const char *assign_hook(const char *newvalue,
+				bool doit,
+				bool interactive)
+The meanings of the parameters are the same as for the other types of GUC
+variables, but the return value is handled differently:
+	NULL --- assignment fails (like returning false for other datatypes)
+	newvalue --- assignment succeeds, assign the newvalue as-is
+	malloc'd (not palloc'd!!!) string --- assign that value instead
+The third choice is allowed in case the assign_hook wants to return a
+"canonical" version of the new value.  For example, the assign_hook for
+datestyle always returns a string that includes both basic datestyle and
+us/euro option, although the input might have specified only one.
+
+If a show_hook is provided, it points to a function of the signature
+	const char *show_hook(void)
+This hook allows variable-specific computation of the value displayed
+by SHOW.
+
+
+SAVING/RESTORING GUC VARIABLE VALUES
+
+Prior values of configuration variables must be remembered in order to
+deal with three special cases: RESET (a/k/a SET TO DEFAULT), rollback of
+SET on transaction abort, and rollback of SET LOCAL at transaction end
+(either commit or abort).  RESET is defined as selecting the value that
+would be effective had there never been any SET commands in the current
+session.
+
+To handle these cases we must keep track of as many as four distinct
+values for each variable.  They are:
+
+* actual variable contents	always the current effective value
+
+* reset_value			the value to use for RESET
+
+* session_value			the "committed" setting for the session
+
+* tentative_value		the uncommitted result of SET
+
+During initialization we set the first three of these (actual, reset_value,
+and session_value) based on whichever non-interactive source has the
+highest priority.  All three will have the same value.
+
+A SET LOCAL command sets the actual variable (and nothing else).  At
+transaction end, the session_value is used to restore the actual variable
+to its pre-transaction value.
+
+A SET (or SET SESSION) command sets the actual variable, and if no error,
+then sets the tentative_value.  If the transaction commits, the
+tentative_value is assigned to the session_value and the actual variable
+(which could by now be different, if the SET was followed by SET LOCAL).
+If the transaction aborts, the tentative_value is discarded and the
+actual variable is restored from the session_value.
+
+RESET is executed like a SET, but using the reset_value as the desired new
+value.  (We do not provide a RESET LOCAL command, but SET LOCAL TO DEFAULT
+has the same behavior that RESET LOCAL would.)  The source associated with
+the reset_value also becomes associated with the actual and session values.
+
+If SIGHUP is received, the GUC code rereads the postgresql.conf
+configuration file (this does not happen in the signal handler, but at
+next return to main loop; note that it can be executed while within a
+transaction).  New values from postgresql.conf are assigned to actual
+variable, reset_value, and session_value, but only if each of these has a
+current source priority <= PGC_S_FILE.  (It is thus possible for
+reset_value to track the config-file setting even if there is currently
+a different interactive value of the actual variable.)
+
+Note that tentative_value is unused and undefined except between a SET
+command and the end of the transaction.  Also notice that we must track
+the source associated with each of the four values.
+
+The assign_hook and show_hook routines work only with the actual variable,
+and are not directly aware of the additional values maintained by GUC.
+This is not a problem for normal usage, since we can assign first to the
+actual variable and then (if that succeeds) to the additional values as
+needed.  However, for SIGHUP rereads we may not want to assign to the
+actual variable.  Our procedure in that case is to call the assign_hook
+with doit = false so that the value is validated, but no derived state is
+changed.
+
+
+STRING MEMORY HANDLING
+
+String option values are allocated with strdup, not with the
+pstrdup/palloc mechanisms.  We would need to keep them in a permanent
+context anyway, and strdup gives us more control over handling
+out-of-memory failures.
+
+We allow a variable's actual value, reset_val, session_val, and
+tentative_val to point at the same storage.  This makes it slightly harder
+to free space (must test that the value to be freed isn't equal to any of
+the other three pointers).  The main advantage is that we never need to
+strdup during transaction commit/abort, so cannot cause an out-of-memory
+failure there.

src/backend/utils/misc/guc-file.l

@@ -4,7 +4,7 @@
  *
  * Copyright 2000 by PostgreSQL Global Development Group
  *
- * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc-file.l,v 1.11 2002/03/02 21:39:33 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/misc/guc-file.l,v 1.12 2002/05/17 01:19:18 tgl Exp $
  */
 
 %{
@@ -168,7 +168,7 @@ ProcessConfigFile(GucContext context)
 	head = tail = NULL;
 	opt_name = opt_value = NULL;
 
-    while((token = yylex()))
+    while ((token = yylex()))
         switch(parse_state)
         {
             case 0: /* no previous input */
@@ -188,23 +188,22 @@ ProcessConfigFile(GucContext context)
                     token = yylex();
 
                 if (token != GUC_ID && token != GUC_STRING && 
-			token != GUC_INTEGER && token != GUC_REAL && 
-			token != GUC_UNQUOTED_STRING)
+					token != GUC_INTEGER && token != GUC_REAL && 
+					token != GUC_UNQUOTED_STRING)
                     goto parse_error;
                 opt_value = strdup(yytext);
 				if (opt_value == NULL)
 					goto out_of_memory;
-		if (token == GUC_STRING)
-		{
-			/* remove the beginning and ending quote/apostrophe */
-			/* first: shift the whole shooting match down one
- 			character */
-			memmove(opt_value,opt_value+1,strlen(opt_value)-1);
-			/* second: null out the 2 characters we shifted */
-                        opt_value[strlen(opt_value)-2]='\0';
-			/* do the escape thing.  free()'s the strdup above */
-			opt_value=GUC_scanstr(opt_value);
-		}
+				if (token == GUC_STRING)
+				{
+					/* remove the beginning and ending quote/apostrophe */
+					/* first: shift the whole thing down one character */
+					memmove(opt_value,opt_value+1,strlen(opt_value)-1);
+					/* second: null out the 2 characters we shifted */
+					opt_value[strlen(opt_value)-2]='\0';
+					/* do the escape thing.  free()'s the strdup above */
+					opt_value=GUC_scanstr(opt_value);
+				}
                 parse_state = 2;
                 break;
 
@@ -241,14 +240,14 @@ ProcessConfigFile(GucContext context)
     for(item = head; item; item=item->next)
 	{
 		if (!set_config_option(item->name, item->value, context,
-							   false, PGC_S_INFINITY))
+							   PGC_S_FILE, false, false))
 			goto cleanup_exit;
 	}
 
     /* If we got here all the options parsed okay. */
 	for(item = head; item; item=item->next)
 		set_config_option(item->name, item->value, context,
-						  true, PGC_S_FILE);
+						  PGC_S_FILE, false, true);
 
  cleanup_exit:
 	free_name_value_list(head);

src/backend/utils/misc/postgresql.conf.sample

@@ -192,7 +192,10 @@
 #
 #dynamic_library_path = '$libdir'
 #search_path = '$user,public'
+#datestyle = 'iso, us'
+#timezone = unknown		# actually, defaults to TZ environment setting
 #australian_timezones = false
+#client_encoding = sql_ascii	# actually, defaults to database encoding
 #authentication_timeout = 60	# min 1, max 600
 #deadlock_timeout = 1000
 #default_transaction_isolation = 'read committed'