Fix more user-visible elog() calls.

Michael Paquier discovered that this could be triggered via SQL;
give a nicer message instead.

Patch by Michael Paquier, reviewed by Masahiko Sawada.

Discussion: http://postgr.es/m/CAB7nPqQtPg+LKKtzdKN26judHcvPZ0s1gNigzOT4j8CYuuuBYg@mail.gmail.com

contrib/test_decoding/expected/replorigin.out

@@ -26,7 +26,14 @@ SELECT pg_replication_origin_drop('test_decoding: temp');
 (1 row)
 
 SELECT pg_replication_origin_drop('test_decoding: temp');
-ERROR:  cache lookup failed for replication origin 'test_decoding: temp'
+ERROR:  replication origin "test_decoding: temp" does not exist
+-- various failure checks for undefined slots
+select pg_replication_origin_advance('test_decoding: temp', '0/1');
+ERROR:  replication origin "test_decoding: temp" does not exist
+select pg_replication_origin_session_setup('test_decoding: temp');
+ERROR:  replication origin "test_decoding: temp" does not exist
+select pg_replication_origin_progress('test_decoding: temp', true);
+ERROR:  replication origin "test_decoding: temp" does not exist
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
  ?column? 
 ----------

contrib/test_decoding/sql/replorigin.sql

@@ -13,6 +13,11 @@ SELECT pg_replication_origin_create('test_decoding: temp');
 SELECT pg_replication_origin_drop('test_decoding: temp');
 SELECT pg_replication_origin_drop('test_decoding: temp');
 
+-- various failure checks for undefined slots
+select pg_replication_origin_advance('test_decoding: temp', '0/1');
+select pg_replication_origin_session_setup('test_decoding: temp');
+select pg_replication_origin_progress('test_decoding: temp', true);
+
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
 
 -- origin tx

src/backend/replication/logical/origin.c

@@ -225,8 +225,10 @@ replorigin_by_name(char *roname, bool missing_ok)
 		ReleaseSysCache(tuple);
 	}
 	else if (!missing_ok)
-		elog(ERROR, "cache lookup failed for replication origin '%s'",
-			 roname);
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("replication origin \"%s\" does not exist",
+						roname)));
 
 	return roident;
 }
@@ -437,8 +439,10 @@ replorigin_by_oid(RepOriginId roident, bool missing_ok, char **roname)
 		*roname = NULL;
 
 		if (!missing_ok)
-			elog(ERROR, "cache lookup failed for replication origin with oid %u",
-				 roident);
+			ereport(ERROR,
+					(errcode(ERRCODE_UNDEFINED_OBJECT),
+					 errmsg("replication origin with OID %u does not exist",
+							roident)));
 
 		return false;
 	}