Make invalid primary_slot_name follow standard GUC error reporting.

Previously, if primary_slot_name was set to an invalid slot name and
the configuration file was reloaded, both the postmaster and all other
backend processes reported a WARNING. With many processes running,
this could produce a flood of duplicate messages. The problem was that
the GUC check hook for primary_slot_name reported errors at WARNING
level via ereport().

This commit changes the check hook to use GUC_check_errdetail() and
GUC_check_errhint() for error reporting. As with other GUC parameters,
this causes non-postmaster processes to log the message at DEBUG3,
so by default, only the postmaster's message appears in the log file.

Backpatch to all supported versions.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Chao Li <lic@highgo.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/CAHGQGwFud-cvthCTfusBfKHBS6Jj6kdAPTdLWKvP2qjUX6L_wA@mail.gmail.com
Backpatch-through: 13

src/backend/replication/slot.c

@@ -163,31 +163,62 @@ ReplicationSlotsShmemInit(void)
 /*
  * Check whether the passed slot name is valid and report errors at elevel.
  *
- * Slot names may consist out of [a-z0-9_]{1,NAMEDATALEN-1} which should allow
- * the name to be used as a directory name on every supported OS.
- *
- * Returns whether the directory name is valid or not if elevel < ERROR.
+ * See comments for ReplicationSlotValidateNameInternal().
  */
 bool
 ReplicationSlotValidateName(const char *name, int elevel)
+{
+	int			err_code;
+	char	   *err_msg = NULL;
+	char	   *err_hint = NULL;
+
+	if (!ReplicationSlotValidateNameInternal(name, &err_code, &err_msg,
+											 &err_hint))
+	{
+		ereport(elevel,
+				errcode(err_code),
+				errmsg_internal("%s", err_msg),
+				(err_hint != NULL) ? errhint("%s", err_hint) : 0);
+
+		pfree(err_msg);
+		if (err_hint != NULL)
+			pfree(err_hint);
+		return false;
+	}
+
+	return true;
+}
+
+/*
+ * Check whether the passed slot name is valid.
+ *
+ * Slot names may consist out of [a-z0-9_]{1,NAMEDATALEN-1} which should allow
+ * the name to be used as a directory name on every supported OS.
+ *
+ * Returns true if the slot name is valid. Otherwise, returns false and stores
+ * the error code, error message, and optional hint in err_code, err_msg, and
+ * err_hint, respectively. The caller is responsible for freeing err_msg and
+ * err_hint, which are palloc'd.
+ */
+bool
+ReplicationSlotValidateNameInternal(const char *name, int *err_code,
+									char **err_msg, char **err_hint)
 {
 	const char *cp;
 
 	if (strlen(name) == 0)
 	{
-		ereport(elevel,
-				(errcode(ERRCODE_INVALID_NAME),
-				 errmsg("replication slot name \"%s\" is too short",
-						name)));
+		*err_code = ERRCODE_INVALID_NAME;
+		*err_msg = psprintf(_("replication slot name \"%s\" is too short"), name);
+		*err_hint = NULL;
 		return false;
 	}
 
 	if (strlen(name) >= NAMEDATALEN)
 	{
-		ereport(elevel,
-				(errcode(ERRCODE_NAME_TOO_LONG),
-				 errmsg("replication slot name \"%s\" is too long",
-						name)));
+		*err_code = ERRCODE_NAME_TOO_LONG;
+		*err_msg = psprintf(_("replication slot name \"%s\" is too long"), name);
+		*err_hint = NULL;
 		return false;
 	}
 
@@ -197,11 +228,9 @@ ReplicationSlotValidateName(const char *name, int elevel)
 			  || (*cp >= '0' && *cp <= '9')
 			  || (*cp == '_')))
 		{
-			ereport(elevel,
-					(errcode(ERRCODE_INVALID_NAME),
-					 errmsg("replication slot name \"%s\" contains invalid character",
-							name),
-					 errhint("Replication slot names may only contain lower case letters, numbers, and the underscore character.")));
+			*err_code = ERRCODE_INVALID_NAME;
+			*err_msg = psprintf(_("replication slot name \"%s\" contains invalid character"), name);
+			*err_hint = psprintf(_("Replication slot names may only contain lower case letters, numbers, and the underscore character."));
 			return false;
 		}
 	}

src/backend/utils/misc/guc.c

@@ -12587,9 +12587,20 @@ assign_recovery_target_lsn(const char *newval, void *extra)
 static bool
 check_primary_slot_name(char **newval, void **extra, GucSource source)
 {
+	int			err_code;
+	char	   *err_msg = NULL;
+	char	   *err_hint = NULL;
+
 	if (*newval && strcmp(*newval, "") != 0 &&
-		!ReplicationSlotValidateName(*newval, WARNING))
+		!ReplicationSlotValidateNameInternal(*newval, &err_code, &err_msg,
+											 &err_hint))
+	{
+		GUC_check_errcode(err_code);
+		GUC_check_errdetail("%s", err_msg);
+		if (err_hint != NULL)
+			GUC_check_errhint("%s", err_hint);
 		return false;
+	}
 
 	return true;
 }

src/include/replication/slot.h

@@ -208,6 +208,8 @@ extern void ReplicationSlotMarkDirty(void);
 
 /* misc stuff */
 extern bool ReplicationSlotValidateName(const char *name, int elevel);
+extern bool ReplicationSlotValidateNameInternal(const char *name,
+												int *err_code, char **err_msg, char **err_hint);
 extern void ReplicationSlotReserveWal(void);
 extern void ReplicationSlotsComputeRequiredXmin(bool already_locked);
 extern void ReplicationSlotsComputeRequiredLSN(void);