[GitHub] garrensmith commented on a change in pull request #469: Choose index based on fields match

[gi...@git.apache.org]

garrensmith commented on a change in pull request #469: Choose index based on fields match
URL: https://github.com/apache/couchdb/pull/469#discussion_r109939494
 
 

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 File path: src/mango/src/mango_cursor_view.erl
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 @@ -107,10 +107,14 @@ execute(#cursor{db = Db, index = Idx} = Cursor0, UserFun, UserAcc) ->
 % check FieldRanges for a, b, c, and d and return
 % the longest prefix of columns found.
 composite_indexes(Indexes, FieldRanges) ->
-    lists:foldl(fun(Idx, Acc) ->
+    FieldKeys = [Key || {Key, _} <- FieldRanges],
+    SortedIndexes = lists:foldl(fun(Idx, Acc) ->
         Cols = mango_idx:columns(Idx),
         Prefix = composite_prefix(Cols, FieldRanges),
-        [{Idx, Prefix} | Acc]
+        % create a score based on how close the number of fields
+        % the index has to the number of fields in the selector
+        Score = length(Cols) - length(FieldKeys),
 
 Review comment:
   I've made an attempt at fixing this. I'm not 100% I fully understood this. In the situation of [a, b, c] and [a, d, e] I've defaulted to the indices names. The only problem with that is there is a possibility of a doc being in one index but not in another and this could lead to unexpected results for a user. 
 
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