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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