[GitHub] [couchdb] oliverdain edited a comment on issue #2124: Mango: do not warn about missing index when only _id is being selected against

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oliverdain edited a comment on issue #2124: Mango: do not warn about missing index when only _id is being selected against
URL: https://github.com/apache/couchdb/issues/2124#issuecomment-598975215
 
 
   Hi @wohali . Thanks for the explanation. I've simplified the real query here to make the bug report simpler but the real query used `_id` *and* some other fields to further limit the results I get. Note that with Mango this is legal and if I do that with an index other than `_all_docs` I do not get a warning. For example, a query like this is, I think, quite reasonable:
   
   ```
   {
      "selector": {
         "$and": [
            {
               "_id": {
                  "$gt": "bar"
               }
            },
            {
               "_id": {
                  "$lt": "foo"
               }
            },
           {
             "other_field": "some value"
           }
         ]
      }
   }
   ```
   
   Assuming there aren't too many docs with `_id` between `bar` and `foo` this is a very useful way to use Mango and the performance is quite good.
   
   I think the desired behavior isn't "suppress the warning when **only** the _id field is being used" but rather something like "suppress the warning when the _id field has significantly reduced the set of documents that must be examined" or whatever the equivalent rule is for a normal Mango index.

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