Replace over-optimistic Assert in partitioning code with a runtime test.

get_partition_parent felt that it could simply Assert that systable_getnext
found a tuple.  This is unlike any other caller of that function, and it's
unsafe IMO --- in fact, the reason I noticed it was that the Assert failed.
(OK, I was working with known-inconsistent catalog contents, but I wasn't
expecting the DB to fall over quite that violently.  The behavior in a
non-assert-enabled build wouldn't be very nice, either.)  Fix it to do what
other callers do, namely an actual runtime-test-and-elog.

Also, standardize the wording of elog messages that are complaining about
unexpected failure of systable_getnext.  90% of them say "could not find
tuple for <object>", so make the remainder do likewise.  Many of the
holdouts were using the phrasing "cache lookup failed", which is outright
misleading since no catcache search is involved.

contrib/sepgsql/database.c

@@ -88,7 +88,7 @@ sepgsql_database_post_create(Oid databaseId, const char *dtemplate)
 							   SnapshotSelf, 1, &skey);
 	tuple = systable_getnext(sscan);
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "catalog lookup failed for database %u", databaseId);
+		elog(ERROR, "could not find tuple for database %u", databaseId);
 
 	datForm = (Form_pg_database) GETSTRUCT(tuple);
 

contrib/sepgsql/proc.c

@@ -68,7 +68,7 @@ sepgsql_proc_post_create(Oid functionId)
 
 	tuple = systable_getnext(sscan);
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "catalog lookup failed for proc %u", functionId);
+		elog(ERROR, "could not find tuple for function %u", functionId);
 
 	proForm = (Form_pg_proc) GETSTRUCT(tuple);
 
@@ -261,7 +261,7 @@ sepgsql_proc_setattr(Oid functionId)
 							   SnapshotSelf, 1, &skey);
 	newtup = systable_getnext(sscan);
 	if (!HeapTupleIsValid(newtup))
-		elog(ERROR, "catalog lookup failed for function %u", functionId);
+		elog(ERROR, "could not find tuple for function %u", functionId);
 	newform = (Form_pg_proc) GETSTRUCT(newtup);
 
 	/*

contrib/sepgsql/relation.c

@@ -83,7 +83,7 @@ sepgsql_attribute_post_create(Oid relOid, AttrNumber attnum)
 
 	tuple = systable_getnext(sscan);
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "catalog lookup failed for column %d of relation %u",
+		elog(ERROR, "could not find tuple for column %d of relation %u",
 			 attnum, relOid);
 
 	attForm = (Form_pg_attribute) GETSTRUCT(tuple);
@@ -271,7 +271,7 @@ sepgsql_relation_post_create(Oid relOid)
 
 	tuple = systable_getnext(sscan);
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "catalog lookup failed for relation %u", relOid);
+		elog(ERROR, "could not find tuple for relation %u", relOid);
 
 	classForm = (Form_pg_class) GETSTRUCT(tuple);
 
@@ -623,7 +623,7 @@ sepgsql_relation_setattr(Oid relOid)
 
 	newtup = systable_getnext(sscan);
 	if (!HeapTupleIsValid(newtup))
-		elog(ERROR, "catalog lookup failed for relation %u", relOid);
+		elog(ERROR, "could not find tuple for relation %u", relOid);
 	newform = (Form_pg_class) GETSTRUCT(newtup);
 
 	/*
@@ -700,7 +700,7 @@ sepgsql_relation_setattr_extra(Relation catalog,
 							   SnapshotSelf, 1, &skey);
 	tuple = systable_getnext(sscan);
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "catalog lookup failed for object %u in catalog \"%s\"",
+		elog(ERROR, "could not find tuple for object %u in catalog \"%s\"",
 			 extra_oid, RelationGetRelationName(catalog));
 
 	datum = heap_getattr(tuple, anum_relation_id,

contrib/sepgsql/schema.c

@@ -67,7 +67,7 @@ sepgsql_schema_post_create(Oid namespaceId)
 							   SnapshotSelf, 1, &skey);
 	tuple = systable_getnext(sscan);
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "catalog lookup failed for namespace %u", namespaceId);
+		elog(ERROR, "could not find tuple for namespace %u", namespaceId);
 
 	nspForm = (Form_pg_namespace) GETSTRUCT(tuple);
 	nsp_name = NameStr(nspForm->nspname);

src/backend/catalog/aclchk.c

@@ -2738,7 +2738,7 @@ ExecGrant_Largeobject(InternalGrant *istmt)
 
 		tuple = systable_getnext(scan);
 		if (!HeapTupleIsValid(tuple))
-			elog(ERROR, "cache lookup failed for large object %u", loid);
+			elog(ERROR, "could not find tuple for large object %u", loid);
 
 		form_lo_meta = (Form_pg_largeobject_metadata) GETSTRUCT(tuple);
 
@@ -5503,7 +5503,7 @@ recordExtObjInitPriv(Oid objoid, Oid classoid)
 
 		tuple = systable_getnext(scan);
 		if (!HeapTupleIsValid(tuple))
-			elog(ERROR, "cache lookup failed for large object %u", objoid);
+			elog(ERROR, "could not find tuple for large object %u", objoid);
 
 		aclDatum = heap_getattr(tuple,
 								Anum_pg_largeobject_metadata_lomacl,

src/backend/catalog/objectaddress.c

@@ -3345,7 +3345,7 @@ getObjectDescription(const ObjectAddress *object)
 				tuple = systable_getnext(sscan);
 
 				if (!HeapTupleIsValid(tuple))
-					elog(ERROR, "cache lookup failed for policy %u",
+					elog(ERROR, "could not find tuple for policy %u",
 						 object->objectId);
 
 				form_policy = (Form_pg_policy) GETSTRUCT(tuple);

src/backend/catalog/partition.c

@@ -874,7 +874,8 @@ get_partition_parent(Oid relid)
 							  NULL, 2, key);
 
 	tuple = systable_getnext(scan);
-	Assert(HeapTupleIsValid(tuple));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "could not find tuple for parent of relation %u", relid);
 
 	form = (Form_pg_inherits) GETSTRUCT(tuple);
 	result = form->inhparent;

src/backend/commands/extension.c

@@ -2387,7 +2387,7 @@ pg_extension_config_dump(PG_FUNCTION_ARGS)
 	extTup = systable_getnext(extScan);
 
 	if (!HeapTupleIsValid(extTup))		/* should not happen */
-		elog(ERROR, "extension with oid %u does not exist",
+		elog(ERROR, "could not find tuple for extension %u",
 			 CurrentExtensionObject);
 
 	memset(repl_val, 0, sizeof(repl_val));
@@ -2535,7 +2535,7 @@ extension_config_remove(Oid extensionoid, Oid tableoid)
 	extTup = systable_getnext(extScan);
 
 	if (!HeapTupleIsValid(extTup))		/* should not happen */
-		elog(ERROR, "extension with oid %u does not exist",
+		elog(ERROR, "could not find tuple for extension %u",
 			 extensionoid);
 
 	/* Search extconfig for the tableoid */
@@ -2736,7 +2736,8 @@ AlterExtensionNamespace(const char *extensionName, const char *newschema, Oid *o
 	extTup = systable_getnext(extScan);
 
 	if (!HeapTupleIsValid(extTup))		/* should not happen */
-		elog(ERROR, "extension with oid %u does not exist", extensionOid);
+		elog(ERROR, "could not find tuple for extension %u",
+			 extensionOid);
 
 	/* Copy tuple so we can modify it below */
 	extTup = heap_copytuple(extTup);
@@ -3057,7 +3058,7 @@ ApplyExtensionUpdates(Oid extensionOid,
 		extTup = systable_getnext(extScan);
 
 		if (!HeapTupleIsValid(extTup))	/* should not happen */
-			elog(ERROR, "extension with oid %u does not exist",
+			elog(ERROR, "could not find tuple for extension %u",
 				 extensionOid);
 
 		extForm = (Form_pg_extension) GETSTRUCT(extTup);

src/backend/utils/adt/ruleutils.c

@@ -1851,7 +1851,7 @@ pg_get_constraintdef_worker(Oid constraintId, bool fullCommand,
 			heap_close(relation, AccessShareLock);
 			return NULL;
 		}
-		elog(ERROR, "cache lookup failed for constraint %u", constraintId);
+		elog(ERROR, "could not find tuple for constraint %u", constraintId);
 	}
 
 	conForm = (Form_pg_constraint) GETSTRUCT(tup);