When the underlying schema for Swarm Search changes, new feeds are required to generate index data in the new format. Swarm Storage allows the creation of more than one Search feed so transitioning from using one feed to another is possible without disruption. Continue using the primary feed for queries during the transition; the second feed is incomplete until it fully clears its backlog. Transition to it (marking it as primary) as soon as reasonable for your operations when the second feed is caught up.
Important
Delete the original feed when verifying the new primary feed target is working. Having two feeds is for temporary use only because every feed incurs cluster activity, even when paused.
Gateway must be be restarted when the primary search feed is changed in Swarm Storage.
Create a new search feed in the Swarm UI. Do not select Make primary.
Wait until the new feed has completed indexing the cluster when the feed shows 0 "pending evaluation".
Make it the primary feed when the new feed is ready. Navigate to Cluster > Feeds, open the new Search feed, and select Make primary from the drop-down menu in the Swarm UI.
Operate with both feeds for several days. In case of any issues during troubleshooting, restore the old feed to the primary feed.
Delete the old feed after this confirmation period. Navigate to Cluster > Feeds, open the old Search feed, and select Delete from the drop-down menu in the Swarm UI.
Delete the old index data to reclaim that space if desired.
curl -XDELETE 'http://old-elasticsearch:9200/_all' # do not do this to your production data!