[GitHub] rnewson commented on issue #1737: Performance regression querying changes using _doc_ids filter

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rnewson commented on issue #1737: Performance regression querying changes using _doc_ids filter
URL: https://github.com/apache/couchdb/issues/1737#issuecomment-438607210
 
 
   ok, I think I get this finally. Before 2.0, we had an optimization for _doc_ids and _design filter;
   
   ```
   commit bfa0a8900163edd4f85c7bbf5b595de9885cfbf9
   Author: Filipe David Borba Manana <fd...@apache.org>
   Date:   Tue Sep 20 22:55:29 2011 +0000
   
       Efficient implementation of builtin filters
   
       Currently, the builtin changes filters "_doc_ids" and "_design"
       are not very efficient because they fold the entire seq btree
       and then filter the values by document ID.
       This implementation avoids that by doing direct lookups against
       the id btree, and then, for continuous changes requests, it
       just listens for database update events and does partial seq
       btree folds.
   
       COUCHDB-1288
   ```
   
   The clustered code for _changes does not use it.
   

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