Add C comment

Add C comment about why we throw an error if the pg_upgrade old/new
database counts don't match.

diff --git a/contrib/pg_upgrade/relfilenode.c b/contrib/pg_upgrade/relfilenode.c
index 9a0a3ac18d9557cf696e452d4e61cab1b9c08485..6fb336cfc53d9ad65f2130e558ca4c8f2b59b406 100644 (file)
--- a/contrib/pg_upgrade/relfilenode.c
+++ b/contrib/pg_upgrade/relfilenode.c
@@ -37,6 +37,12 @@ transfer_all_new_dbs(DbInfoArr *old_db_arr,
 
        prep_status("Restoring user relation files\n");
 
+       /*
+        *      If the user removed the 'postgres' database from the old cluster,
+        *      this will cause the database counts to not match and throw an error.
+        *      We could allow this to work because the new database is empty (we
+        *      checked), but we don't.
+        */
        if (old_db_arr->ndbs != new_db_arr->ndbs)
                pg_log(PG_FATAL, "old and new clusters have a different number of databases\n");