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.