garethbowen opened a new issue #1737: Performance regression querying changes using _doc_ids filter URL: https://github.com/apache/couchdb/issues/1737 When upgrading from v1.7.1 to v2.2.0 I noticed our replication was taking longer. I investigated further and found the problem was specifically in relation to the initial request for changes. We use the _doc_ids filter so we can replicate only certain documents and this has been stable and performant on the 1.x versions. ## Steps to Reproduce Use [this node script](https://github.com/apache/couchdb/files/2578449/index.js.txt) to create a database and fill it with 1 million docs and then query it for specific IDs. ## Context In my testing using the above script I got responses in 1 to 2ms on v1.7.1 and 2500 to 2600ms on 2.2.0. In our production database with real world data and about 8 million docs it takes less than a second on v1.7.1 and around 40 seconds on v2.2.0. This has affected real world performance for users trying to replicate their data. ## Your Environment * Version used: 2.2.0 (from 1.7.1) * Operating System: Ubuntu 1804 * Link to your project: https://github.com/medic/medic-webapp/ ## What I've tried - changing clustering from n=3 q=8 to n=1 q=1 - no improvement - changing the `changes_doc_ids_optimization_threshold` at 1, 100, and very large - no improvement - using a very large `seq_interval` parameter - no improvement - using a mango selector - worse performance
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