diff --git a/src/backend/replication/logical/relation.c b/src/backend/replication/logical/relation.c
index 9ee70a2..4f31c95 100644
--- a/src/backend/replication/logical/relation.c
+++ b/src/backend/replication/logical/relation.c
@@ -1,6 +1,6 @@
 /*-------------------------------------------------------------------------
  * relation.c
- *	   PostgreSQL logical replication
+ *	   PostgreSQL logical replication relation mapping cache
  *
  * Copyright (c) 2016-2020, PostgreSQL Global Development Group
  *
@@ -8,8 +8,19 @@
  *	  src/backend/replication/logical/relation.c
  *
  * NOTES
- *	  This file contains helper functions for logical replication relation
- *	  mapping cache.
+ *	  Routines in this file mainly have to do with mapping the proprties of
+ *	  local replication  target relations to the properties of their remote
+ *	  counterpart.  This mapping is maintained in a LogicalRepRelMapEntry
+ *	  struct per target relation, cached in a local hash table keyed by the
+ *	  remote relation OID.
+ *
+ *	  Since replication actions targeting partitioned tables need to be
+ *	  applied to their leaf partitions instead, the mapping info must be
+ *	  maintained for each partition separately, even though all point to the
+ *	  same remote relation.  For that case, in addition to the target
+ *	  partitioned table's LogicalRepRelMapEntry, there is
+ *	  LogicalRepPartMapEntry for every partition touched so far, cached in
+ *	  another hash table which is keyed by partition OID.
  *
  *-------------------------------------------------------------------------
  */