pg_upgrade: improve C comment about what old/new oids match

diff --git a/contrib/pg_upgrade/pg_upgrade.c b/contrib/pg_upgrade/pg_upgrade.c
index b992cadbc50c1ef904a32df419396a0fe8e4d850..5e21028506029bd42a4577a675e634f323e7688b 100644 (file)
--- a/contrib/pg_upgrade/pg_upgrade.c
+++ b/contrib/pg_upgrade/pg_upgrade.c
@@ -15,13 +15,12 @@
  *     oids are the same between old and new clusters.  This is important
  *     because toast oids are stored as toast pointers in user tables.
  *
- *     FYI, while pg_class.oid and pg_class.relfilenode are initially the same
- *     in a cluster, but they can diverge due to CLUSTER, REINDEX, or VACUUM
- *     FULL.  The new cluster will have matching pg_class.oid and
- *     pg_class.relfilenode values and be based on the old oid value.  This can
- *     cause the old and new pg_class.relfilenode values to differ.  In summary,
- *     old and new pg_class.oid and new pg_class.relfilenode will have the
- *     same value, and old pg_class.relfilenode might differ.
+ *     While pg_class.oid and pg_class.relfilenode are initially the same
+ *     in a cluster, they can diverge due to CLUSTER, REINDEX, or VACUUM
+ *     FULL.  In the new cluster, pg_class.oid and pg_class.relfilenode will
+ *     be the same and will match the old pg_class.oid value.  Because of
+ *     this, old/new pg_class.relfilenode values will not match if CLUSTER,
+ *     REINDEX, or VACUUM FULL have been performed in the old cluster.
  *
  *     We control all assignments of pg_type.oid because these oids are stored
  *     in user composite type values.