Refactor routines for subscription and publication lookups

Those routines gain a missing_ok argument, allowing a caller to get a
NULL result instead of an error if set to true.  This is part of a
larger refactoring effort for objectaddress.c where trying to check for
non-existing objects does not result in cache lookup failures.

Author: Michael Paquier
Reviewed-by: Aleksander Alekseev, Álvaro Herrera
Discussion: https://postgr.es/m/CAB7nPqSZxrSmdHK-rny7z8mi=EAFXJ5J-0RbzDw6aus=wB5azQ@mail.gmail.com

src/backend/catalog/objectaddress.c

@@ -3508,7 +3508,8 @@ getObjectDescription(const ObjectAddress *object)
 		case OCLASS_PUBLICATION:
 			{
 				appendStringInfo(&buffer, _("publication %s"),
-								 get_publication_name(object->objectId));
+								 get_publication_name(object->objectId,
+													  false));
 				break;
 			}
 
@@ -3526,7 +3527,7 @@ getObjectDescription(const ObjectAddress *object)
 						 object->objectId);
 
 				prform = (Form_pg_publication_rel) GETSTRUCT(tup);
-				pubname = get_publication_name(prform->prpubid);
+				pubname = get_publication_name(prform->prpubid, false);
 
 				initStringInfo(&rel);
 				getRelationDescription(&rel, prform->prrelid);
@@ -3542,7 +3543,8 @@ getObjectDescription(const ObjectAddress *object)
 		case OCLASS_SUBSCRIPTION:
 			{
 				appendStringInfo(&buffer, _("subscription %s"),
-								 get_subscription_name(object->objectId));
+								 get_subscription_name(object->objectId,
+													   false));
 				break;
 			}
 
@@ -5042,7 +5044,7 @@ getObjectIdentityParts(const ObjectAddress *object,
 			{
 				char	   *pubname;
 
-				pubname = get_publication_name(object->objectId);
+				pubname = get_publication_name(object->objectId, false);
 				appendStringInfoString(&buffer,
 									   quote_identifier(pubname));
 				if (objname)
@@ -5063,7 +5065,7 @@ getObjectIdentityParts(const ObjectAddress *object,
 						 object->objectId);
 
 				prform = (Form_pg_publication_rel) GETSTRUCT(tup);
-				pubname = get_publication_name(prform->prpubid);
+				pubname = get_publication_name(prform->prpubid, false);
 
 				getRelationIdentity(&buffer, prform->prrelid, objname);
 				appendStringInfo(&buffer, " in publication %s", pubname);
@@ -5079,7 +5081,7 @@ getObjectIdentityParts(const ObjectAddress *object,
 			{
 				char	   *subname;
 
-				subname = get_subscription_name(object->objectId);
+				subname = get_subscription_name(object->objectId, false);
 				appendStringInfoString(&buffer,
 									   quote_identifier(subname));
 				if (objname)

src/backend/catalog/pg_publication.c

@@ -427,9 +427,12 @@ get_publication_oid(const char *pubname, bool missing_ok)
 
 /*
  * get_publication_name - given a publication Oid, look up the name
+ *
+ * If missing_ok is false, throw an error if name not found.  If true, just
+ * return NULL.
  */
 char *
-get_publication_name(Oid pubid)
+get_publication_name(Oid pubid, bool missing_ok)
 {
 	HeapTuple	tup;
 	char	   *pubname;
@@ -438,7 +441,11 @@ get_publication_name(Oid pubid)
 	tup = SearchSysCache1(PUBLICATIONOID, ObjectIdGetDatum(pubid));
 
 	if (!HeapTupleIsValid(tup))
-		elog(ERROR, "cache lookup failed for publication %u", pubid);
+	{
+		if (!missing_ok)
+			elog(ERROR, "cache lookup failed for publication %u", pubid);
+		return NULL;
+	}
 
 	pubform = (Form_pg_publication) GETSTRUCT(tup);
 	pubname = pstrdup(NameStr(pubform->pubname));

src/backend/catalog/pg_subscription.c

@@ -179,9 +179,12 @@ get_subscription_oid(const char *subname, bool missing_ok)
 
 /*
  * get_subscription_name - given a subscription OID, look up the name
+ *
+ * If missing_ok is false, throw an error if name not found.  If true, just
+ * return NULL.
  */
 char *
-get_subscription_name(Oid subid)
+get_subscription_name(Oid subid, bool missing_ok)
 {
 	HeapTuple	tup;
 	char	   *subname;
@@ -190,7 +193,11 @@ get_subscription_name(Oid subid)
 	tup = SearchSysCache1(SUBSCRIPTIONOID, ObjectIdGetDatum(subid));
 
 	if (!HeapTupleIsValid(tup))
-		elog(ERROR, "cache lookup failed for subscription %u", subid);
+	{
+		if (!missing_ok)
+			elog(ERROR, "cache lookup failed for subscription %u", subid);
+		return NULL;
+	}
 
 	subform = (Form_pg_subscription) GETSTRUCT(tup);
 	subname = pstrdup(NameStr(subform->subname));

src/include/catalog/pg_publication.h

@@ -88,7 +88,7 @@ extern ObjectAddress publication_add_relation(Oid pubid, Relation targetrel,
 						 bool if_not_exists);
 
 extern Oid	get_publication_oid(const char *pubname, bool missing_ok);
-extern char *get_publication_name(Oid pubid);
+extern char *get_publication_name(Oid pubid, bool missing_ok);
 
 extern Datum pg_get_publication_tables(PG_FUNCTION_ARGS);
 

src/include/catalog/pg_subscription.h

@@ -80,7 +80,7 @@ typedef struct Subscription
 extern Subscription *GetSubscription(Oid subid, bool missing_ok);
 extern void FreeSubscription(Subscription *sub);
 extern Oid	get_subscription_oid(const char *subname, bool missing_ok);
-extern char *get_subscription_name(Oid subid);
+extern char *get_subscription_name(Oid subid, bool missing_ok);
 
 extern int	CountDBSubscriptions(Oid dbid);