4.5. View recommendations — Apache CouchDB® 3.2 Documentation

# 4.5. View recommendations

Here are some tips and tricks for working with CouchDB’s (JavaScript-based) views.

## 4.5.1. Deploying a view change in a live environment

It is possible to change the definition of a view, build the index, then make those changes go live without causing downtime for your application. The trick to making this work is that CouchDB’s JavaScript view index files are based on the contents of the design document - not its name, `_id` or revision. This means that two design documents with identical view code will share the same on-disk view index files.

Here is a worked example, assuming your `/db/_design/ddoc` needs tobe updated.

1. Upload the old design doc to `/db/_design/ddoc-old` (or copy the document) if you want an easy way to rollback in case of problems. The `ddoc-old` document will reference the same view indexes already built for `_design/ddoc`.
2. Upload the updated design doc to `/db/_design/ddoc-new`.
3. Query a view in the new design document to trigger secondary index generation. You can track the indexing progress via the `/_active_tasks` endpoint, or through the Fauxton web interface.
4. When the index is done being built, re-upload the updated design document to `/db/_design/ddoc` (or copy the document). The `ddoc` document will now reference the same view indexes already built for `_design/ddoc-new`.
5. Delete `/db/_design/ddoc-new` and/or `/db/_design/ddoc-old` at your discretion. Don’t forget to trigger Views cleanup to reclaim disk space after deleting `ddoc-old`.

The COPY HTTP verb can be used to copy the design document with a single command:

    curl -X COPY <URL of source design document> -H "Destination: <ID of destination design document>"