[COUCHDB-1398] improve view filtering in changes

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 1.3, 2.0.0
• Component/s: View Server Support
• Labels: changes view
• Skill Level: Committers Level (Medium to Hard)
• Assignee: Unassigned
• Reporter: Benoit Chesneau
• Created: 02/Feb/12 23:05
• Updated: 02/Sep/18 06:36
• Resolved: 02/Sep/18 06:36

Description

Improve the native view filter `_view` support by really using view index. This patches add following features

• small refactoring: create the couch_httpd_changes modules, to put all the changes http support in its own module instead having it in couch_httpd_db.
• add the `view_updated` event when a view index is updated : {view_updated,
  Unknown macro: {DbName, IndexName}

  }

• start the feed using results in the view index instead of all the db index
• only react on view index changes.

For now next changes are still get using the couch_db:changes_since function and passing the map function to the results. It could be improved if we had a by_seq btree in the view index too. Other way may be to skip a number of the documents already processed. Not sure it would be faster. Thoughts ?

The branch couch_view_changes in my repo contains preliminary support:

https://github.com/benoitc/couchdb/tree/couch_view_changes

Diff:
https://github.com/benoitc/couchdb/compare/master...couch_view_changes

To use it, use the native filter named _view which take the parameter view=DesignName/Viewname

eg:

http://server/db/_changes?feed=continuous&heartbeat=true&filter=_view&view=DesignName/SomeView

It has also an interresting side effect: on each db updates the view index refresh is triggered so view updates are triggered. Maybe we could introduce an optionnal parameter to not trigger them though?