I've created a new shared catalog table pg_shdescription to store

comments on cluster global objects like databases, tablespaces, and
roles.

It touches a lot of places, but not much in the way of big changes.  The
only design decision I made was to duplicate the query and manipulation
functions rather than to try and have them handle both shared and local
comments.  I believe this is simpler for the code and not an issue for
callers because they know what type of object they are dealing with.
This has resulted in a shobj_description function analagous to
obj_description and backend functions [Create/Delete]SharedComments
mirroring the existing [Create/Delete]Comments functions.

pg_shdescription.h goes into src/include/catalog/

Kris Jurka

src/include/commands/comment.h

@@ -21,7 +21,8 @@
  * related routines.  CommentObject() implements the SQL "COMMENT ON"
  * command.  DeleteComments() deletes all comments for an object.
  * CreateComments creates (or deletes, if comment is NULL) a comment
- * for a specific key.
+ * for a specific key.  There are versions of these two methods for
+ * both normal and shared objects.
  *------------------------------------------------------------------
  */
 
@@ -31,4 +32,8 @@ extern void DeleteComments(Oid oid, Oid classoid, int32 subid);
 
 extern void CreateComments(Oid oid, Oid classoid, int32 subid, char *comment);
 
+extern void DeleteSharedComments(Oid oid, Oid classoid);
+
+extern void CreateSharedComments(Oid oid, Oid classoid, char *comment);
+
 #endif   /* COMMENT_H */