Fix ALTER SYSTEM to cope with duplicate entries in postgresql.auto.conf.

tglsfdc · tglsfdc · commit f8c9a08520ee · 2019-08-14T15:09:20.000-04:00
ALTER SYSTEM itself normally won't make duplicate entries (although up till this patch, it was possible to confuse it by writing case variants of a GUC's name). However, if some external tool has appended entries to the file, that could result in duplicate entries for a single GUC name. In such a situation, ALTER SYSTEM did exactly the wrong thing, because it replaced or removed only the first matching entry, leaving the later one(s) still there and hence still determining the active value. This patch fixes that by making ALTER SYSTEM sweep through the file and remove all matching entries, then (if not ALTER SYSTEM RESET) append the new setting to the end. This means entries will be in order of last setting rather than first setting, but that shouldn't hurt anything. Also, make the comparisons case-insensitive so that the right things happen if you do, say, ALTER SYSTEM SET "TimeZone" = 'whatever'. This has been broken since ALTER SYSTEM was invented, so back-patch to all supported branches. Ian Barwick, with minor mods by me Discussion: https://postgr.es/m/aed6cc9f-98f3-2693-ac81-52bb0052307e@2ndquadrant.com
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
@@ -7046,40 +7046,37 @@ replace_auto_config_value(ConfigVariable **head_p, ConfigVariable **tail_p,
 						  const char *name, const char *value)
 {
 	ConfigVariable *item,
+			   *next,
 			   *prev = NULL;
 
-	/* Search the list for an existing match (we assume there's only one) */
-	for (item = *head_p; item != NULL; item = item->next)
+	/*
+	 * Remove any existing match(es) for "name".  Normally there'd be at most
+	 * one, but if external tools have modified the config file, there could
+	 * be more.
+	 */
+	for (item = *head_p; item != NULL; item = next)
 	{
-		if (strcmp(item->name, name) == 0)
+		next = item->next;
+		if (guc_name_compare(item->name, name) == 0)
 		{
-			/* found a match, replace it */
-			pfree(item->value);
-			if (value != NULL)
-			{
-				/* update the parameter value */
-				item->value = pstrdup(value);
-			}
+			/* found a match, delete it */
+			if (prev)
+				prev->next = next;
 			else
-			{
-				/* delete the configuration parameter from list */
-				if (*head_p == item)
-					*head_p = item->next;
-				else
-					prev->next = item->next;
-				if (*tail_p == item)
-					*tail_p = prev;
+				*head_p = next;
+			if (next == NULL)
+				*tail_p = prev;
 
-				pfree(item->name);
-				pfree(item->filename);
-				pfree(item);
-			}
-			return;
+			pfree(item->name);
+			pfree(item->value);
+			pfree(item->filename);
+			pfree(item);
 		}
-		prev = item;
+		else
+			prev = item;
 	}
 
-	/* Not there; no work if we're trying to delete it */
+	/* Done if we're trying to delete it */
 	if (value == NULL)
 		return;
 
