[GitHub] tonysun83 commented on a change in pull request #1069: Mango: change catch-all field range priority

[GitBox <gi...@apache.org>]

tonysun83 commented on a change in pull request #1069: Mango: change catch-all field range priority
URL: https://github.com/apache/couchdb/pull/1069#discussion_r157562091
 
 

 ##########
 File path: src/mango/src/mango_cursor_special.erl
 ##########
 @@ -31,10 +31,12 @@
 create(Db, Indexes, Selector, Opts) ->
     InitialRange = mango_idx_view:field_ranges(Selector),
     CatchAll = [{<<"_id">>, {'$gt', null, '$lt', mango_json_max}}],
-    FieldRanges = lists:append(CatchAll, InitialRange),
+    % order matters here - we only want to use the catchall index
+    % if no other range can fulfill the query (because we know)
+    % catchall is the most expensive range
+    FieldRanges = InitialRange ++ CatchAll,
     Composited = mango_cursor_view:composite_indexes(Indexes, FieldRanges),
     {Index, IndexRanges} = mango_cursor_view:choose_best_index(Db, Composited),
-
 
 Review comment:
   whitespace change

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