[GitHub] [couchdb] nickva commented on a diff in pull request #4554: feat(`mango`): add `keys_examined` for `execution_stats` (part 1)

["nickva (via GitHub)" <gi...@apache.org>]

nickva commented on code in PR #4554:
URL: https://github.com/apache/couchdb/pull/4554#discussion_r1181645292


##########
src/mango/src/mango_cursor_view.erl:
##########
@@ -457,12 +480,21 @@ handle_message({row, Props}, Cursor) ->
             couch_log:error("~s :: Error loading doc: ~p", [?MODULE, Error]),
             {ok, Cursor}
     end;
-handle_message({execution_stats, ShardStats}, #cursor{execution_stats = Stats} = Cursor) ->
-    {docs_examined, DocsExamined} = ShardStats,
-    Cursor1 = Cursor#cursor{
+% TODO: remove clause couchdb 4 -- mixed-version upgrade support
+handle_message(
+    {execution_stats, {docs_examined, DocsExamined}}, #cursor{execution_stats = Stats} = Cursor0

Review Comment:
   Tiny nit: It might look better pick out `Stats` in a separate line after the function head, since with the `{execution_stats, {docs_examined, DocsExamined}}` the head is getting rather long.
   
   Also, in the second clause it might be better to explicitly assert we're matching on a map.
   
   ```erlang
   handle_message({execution_stats, {docs_examined, DocsExamined}}, #cursor{} = Cursor0) ->
       #cursor{execution_stats = Stats} = Cursor0,
       ...
   handle_message({execution_stats, #{} = ShardStats}, #cursor{} = Cursor0) ->
       #cursor{execution_stats = Stats} = Cursor0,
       ...  
   
   ```



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