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From: Nathan Bossart <nathan@postgresql.org>
Subject: [PATCH v2 1/1] Allow resetting unknown custom GUCs with reserved prefixes.
Date: Wed, 25 Jun 2025 10:54:33 -0500

---
 src/backend/utils/misc/guc.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 667df448732..a75960d2b0b 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -6711,6 +6711,7 @@ validate_option_array_item(const char *name, const char *value,
 
 {
 	struct config_generic *gconf;
+	bool		reset_custom;
 
 	/*
 	 * There are three cases to consider:
@@ -6729,16 +6730,28 @@ validate_option_array_item(const char *name, const char *value,
 	 * it's assumed to be fully validated.)
 	 *
 	 * name is not known and can't be created as a placeholder.  Throw error,
-	 * unless skipIfNoPermissions is true, in which case return false.
+	 * unless skipIfNoPermissions or reset_custom is true.  If find_option()
+	 * returns false and reset_custom is true, this is a RESET or RESET ALL
+	 * operation for an unknown custom GUC with a reserved prefix, in which
+	 * case we want to fall through to the placeholder check described in the
+	 * preceding paragraph (else there'd be no way for users to remove them).
+	 * Otherwise, if find_option() returns false, return false here, too.
 	 */
-	gconf = find_option(name, true, skipIfNoPermissions, ERROR);
-	if (!gconf)
+	reset_custom = (!value && valid_custom_variable_name(name));
+	gconf = find_option(name, true, skipIfNoPermissions || reset_custom, ERROR);
+	if (!gconf && !reset_custom)
 	{
 		/* not known, failed to make a placeholder */
 		return false;
 	}
 
-	if (gconf->flags & GUC_CUSTOM_PLACEHOLDER)
+	/*
+	 * If we reach this point and gconf is NULL, we know we're dealing with a
+	 * RESET or RESET ALL command for an unknown custom GUC with a reserved
+	 * prefix.  We treat that the same as if a placeholder was created, else
+	 * there'd be no way for users to remove them.
+	 */
+	if (!gconf || gconf->flags & GUC_CUSTOM_PLACEHOLDER)
 	{
 		/*
 		 * We cannot do any meaningful check on the value, so only permissions
-- 
2.39.5 (Apple Git-154)


--tHVdw3fiIHnjo3EY--

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